JPred4: a protein secondary structure prediction server

RNAi-Mediated Knockdown of Tektins Does Not Affect Male Fertility in Lygus hesperus

Mirid plant bugs (Hemiptera: Miridae), including Lygus hesperus (western tarnished plant bug), are key pests of numerous agricultural crops. While management of this pest relies heavily on chemical insecticides, the evolution of resistance and environmental concerns underscore the need for new and more effective approaches. Genetic-based strategies that target male fertiliy are currently being evaluated for population suppression. However, a lack of candidate gene targets with appropriate function, specifically in non-model species like L. hesperus, has hindered progress in the development and application of such approaches. Given their conserved role in stabilization of the flagella axoneme and association with sperm motility in many organisms, members of the tektin gene family represent logical targets for genetic-based sterilization. Here, we identified four homologs of the non-vertebrate tektin family from L. hesperus and used RNA interference-mediated knockdown to assess their roles in male fertility. Although transcription of the four tektins was predominantly in the testis, knockdown had negligible effects on either sperm abundance or male fertility. Our results suggest that tektins do not play a critical role in sperm fertilization of eggs in L. hesperus and are thus likely poor targets for genetic-based sterilization approaches in this species.

Unveiling the structural and functional implications of uncharacterized NSPs and variations in the molecular toolkit across arteriviruses

Despite considerable scrutiny of mammalian arterivirus genomes, their genomic architecture remains incomplete, with several unannotated non-structural proteins (NSPs) and the enigmatic absence of methyltransferase (MTase) domains. Additionally, the host range of arteriviruses has expanded to include seven newly sequenced genomes from non-mammalian hosts, which remain largely unannotated and await detailed comparisons alongside mammalian isolates. Utilizing comparative genomics approaches and comprehensive sequence-structure analysis, we provide enhanced genomic architecture and annotations for arterivirus genomes. We identified the previously unannotated C-terminal domain of NSP3 as a winged helix-turn-helix domain and classified NSP7 as a new small β-barrel domain, both likely involved in interactions with viral RNA. NSP12 is identified as a derived variant of the N7-MTase-like Rossmann fold domain that retains core structural alignment with N7-MTases in Nidovirales but likely lacks enzymatic functionality due to the erosion of catalytic residues, indicating a unique role specific to mammalian arteriviruses. In contrast, non-mammalian arteriviruses sporadically retain a 2'-O-MTase and an exonuclease (ExoN) domain, which are typically absent in mammalian arteriviruses, highlighting contrasting evolutionary trends and variations in their molecular toolkit. Similar lineage-specific patterns are observed in the diversification of papain-like proteases and structural proteins. Overall, the study extends our knowledge of arterivirus genomic diversity and evolution.

Simulation of Neurotrophin Receptor Transmembrane Helix Interactions Reveals Active States and Distinct Signaling Mechanisms

Neurotrophin (NT) receptor signaling regulates neuronal survival, axonal and dendritic network maintenance, differentiation, and synaptic plasticity. Signaling is initiated by binding of NT to the extracellular domain of NT receptor dimers, leading to activation of the receptor and signal propagation intracellularly. How this activating signal is mediated by the single-pass transmembrane (TM) helical domain of the receptor and what the relation between domain sequence and signaling mechanism is remain unclear. The structure and dynamics of the TM domain of the receptor dimers in the active and inactive states for intracellular signaling are still elusive, with NMR structures capturing only a single state. Here, we carried out unbiased and enhanced sampling molecular dynamics simulations of the TM domain dimers of the wild-type p75, TrkA and TrkB NT receptors and selected mutants in micelle and bilayer lipid environments at atomistic and coarse-grained levels of representation. The coarse-grained simulations enabled exploration of multiple states of the TM domain dimers and revealed the influence of the lipid environment on the TM helix arrangements. From the simulations, we identify active and inactive TM helix arrangements of the p75 and TrkA receptors that are supported by experimental data and suggest two different signaling mechanisms through the C-terminal regions of the TM helices. For TrkB, a single dominant but less energetically stable arrangement of the TM domain dimer is observed. These findings have implications for mechanistic studies of NT receptor signaling and the design of neuroprotective drugs to stabilize specific states of the TM domain of the receptors.

Molecular Basis for Vacuolar Iron Transport by OsVIT2, a Target for Iron Biofortification in Rice

Iron deficiency is the prevalent and most widespread nutritional shortfall for humans, affecting over 30% of the global population and leading to anemia, particularly among preschool-aged children and pregnant women in developing countries. Simultaneously, while half of the world's population depends on rice (Oryza sativa L.) as a staple food, this cereal does not provide a sufficient amount of that micronutrient to meet these people's nutritional needs: even when iron is readily available in the soil, it does not accumulate in the consumed portion of the grain, namely, the starchy endosperm, being instead retained in the aleurone layer, in the pericarp and in the embryo. In this context, the present work applies computational biology tools-such as normal mode analysis and molecular dynamics simulations-to elucidate the behavior and transport mechanism of the Vacuolar Iron Transporter 2 (OsVIT2), a central protein for iron homeostasis in rice, with the objective of laying the foundations for future OsVIT2 engineering projects that could be articulated with ongoing efforts to promote iron biofortification in rice. We shed light on the interplay between protonation state, configuration and hydration of OsVIT2's pore; on the mechanics of its opening and on the ever-shifting hydrogen bond network contained within it. We also explore the potential contribution of the "flexible arms" to the iron-capturing function performed by the cytoplasmic domain.

Di-HAMP domains of a cytoplasmic chemoreceptor modulate nucleoid array formation and downstream signaling

In bacterial chemosensing, environmental cues are typically sensed by bacterial transmembrane receptors known as methyl-accepting chemotaxis proteins (MCPs). MCPs form highly organized arrays using the bacterial membrane as a scaffold. These arrays amplify the signals and transduce them into a cellular response. The FrzCD cytoplasmic receptor from Myxococcus xanthus is unique due to its ability to bind DNA and use the nucleoid as a scaffold to form arrays. In this study, we identified two HAMP (histidine kinase, adenylyl cyclase, MCP, and phosphatase) domains located between the DNA binding and signaling domains of FrzCD. In vitro experiments demonstrate that the di-HAMP domain restricts FrzCD to a dimeric form in solution and modulate FrzCD affinity for DNA, whereas the signaling domain stabilizes higher-order oligomeric assemblies upon DNA binding. Through fluorescence microscopy and analyses of M. xanthus social behavior, we demonstrate that the impact of the FrzCD HAMP domains on DNA binding and oligomerization significantly influences the formation of Frz clusters on the nucleoid as well as group motility and development. Our results suggest that the di-HAMP domain might have roles not only in signal transduction but also in the plasticity of chemosensory arrays. These observations illustrate mechanisms of regulation of a DNA-bound cytoplasmic array formed by a diffusible MCP.IMPORTANCEOur study identifies the presence of a di-HAMP domain in a cytoplasmic chemoreceptor, FrzCD, from Myxococcus xanthus, and highlights its role in dynamic receptor oligomerization on a DNA scaffold. By controlling receptor oligomerization and subsequently the array formation on the nucleoid, the di-HAMP domain imparts plasticity to receptor arrays. Such plasticity governs cellular responses to external signals and dictates bacterial social behaviors such as group motility and multicellular structure formation.

Characterization of the E26H Mutant Schistosoma japonicum Glutathione S-Transferase

Glutathione-S-transferase, such as that of Schistosoma japonicum (sjGST) belongs to the most widely utilized fusion tags in the recombinant protein technology. The E26H mutation of sjGST has already been found to remarkably improve its ability for binding divalent ions, enabling its purification with immobilized metal affinity chromatography (IMAC). Nevertheless, most characteristics of this mutant remained unexplored to date. In this study, we performed a comparative analysis of the wild-type and the E26H mutant sjGST by using in vitro as well as in silico approaches. We confirmed that the sjGST(E26H) protein exhibits significantly increased affinity for binding nickel ions as compared to the wild-type. In addition, we proved that the sjGST(E26H) can be purified efficiently either with glutathione- or immobilized metal ion-affinity chromatography, even in consecutive purification steps. The human retroviral-like aspartic protease 1 (ASPRV1) conjugated with the sjGST(E26H) fusion tag was also successfully purified by using both of these affinity chromatographic approaches. Our studies revealed that the E26H mutant sjGST can be used as a versatile affinity tag because the modified protein retains the kinetic features of the wild-type and its affinity towards glutathione, while can be purified efficiently by IMAC, as well.

Functional Differences Between Neuronal and Non-neuronal Isoforms of Drebrin

Actin cytoskeleton is vital for neuronal function. Drebrin is a key F-actin binding protein in neurons which is linked to the filaments' stabilization. As mammalian brain develops, drebrin expression pattern switches from non-neuronal (drebrin E, Embryonic) to neuron-specific isoform (drebrin A, Adult), but the evolutionary need for such a switch is enigmatic. Prior in cellulo and in vivo work suggested a non-redundant role of drebrin isoforms in neuronal development and function, however, molecular level understanding of it is lacking. Here we used mutagenesis, bulk solution assays, and time-lapse TIRF microscopy to probe for functional differences between drebrin isoforms. We found that drebrin A and E are functionally distinct and differ in their ability to inhibit F-actin depolymerization. We showed that both isoforms act as permissive cappers of the barbed end of actin, however, drebrin A has a significantly stronger capping activity, compared to that of the non-neuronal drebrin E. Probing for the molecular level insights on the observed differences revealed that the adult-specific exon in neuronal drebrin A contains an actin binding interface which enhances its permissive capping activity. Strikingly, F-actin decoration by neuronal drebrin A confers significantly stronger resistance to cofilin-mediated severing compared to that of drebrin E. Our results provide novel molecular level insights on functional differences between drebrin isoforms, which deepen our understanding of cytoskeletal regulation in the neuronal context. Our results also helps interpreting the previously reported data related to the silencing or knockout of the neuronal drebrin isoform.

The Spc105/Kre28 complex promotes mitotic error correction by outer kinetochore recruitment of Ipl1/Sli15

Kinetochores link chromosomes to dynamic microtubules of the mitotic spindle. To ensure equal chromosome segregation, sister chromatids must achieve biorientation. The conserved kinase Aurora B phosphorylates outer kinetochore proteins on attachments lacking tension, allowing the re-establishment of new connections until biorientation is achieved. Aurora B localizes to the centromere as part of the chromosomal passenger complex (CPC), but the underlying recruitment pathways can be eliminated without disrupting biorientation. It therefore remains unclear how the kinase operates during error correction. Here, we identify the conserved Spc105/Kre28 complex as an outer kinetochore receptor of the Aurora kinase Ipl1 and its activator Sli15 in Saccharomyces cerevisiae. We show that mutations in the helix bundle domain of Spc105/Kre28 impair mitotic error correction, resembling the effects of ipl1 or sli15 mutants. The defects can be suppressed by the artificial recruitment of Ipl1. In biochemical experiments, Ipl1/Sli15 directly associates with Spc105/Kre28, and a conserved segment in the Sli15 central domain is crucially involved in the binding mechanism. These results have important implications for the mechanism of tension-dependent error correction during chromosome biorientation.

A conserved motif in Henipavirus P/V/W proteins drives the fibrillation of the W protein from Hendra virus

The Hendra (HeV) and Nipah (NiV) viruses are high-priority, biosafety level-4 pathogens that cause fatal neurological and respiratory disease. Their P gene encodes not only the P protein, an essential polymerase cofactor, but also the virulence factors V and W. We previously showed that the W protein of HeV (WHeV) forms amyloid-like fibrils and that one of its subdomains, PNT3, fibrillates in isolation. However, the fibrillation kinetics is much faster in the case of the full-length WHeV compared to PNT3, suggesting that another WHeV region contributes to the fibrillation process. In this work, we identified the region spanning residues 2-110 (PNT1) as the crucial region implicated in WHeV fibrillation. Through site-directed mutagenesis, combined with thioflavin T binding experiments and negative-staining transmission electron microscopy, we showed that a predicted cryptic amyloidogenic region (CAR) within PNT1 is the main driver of fibrillation and deciphered the underlying molecular mechanism. Using FTIR, we showed that PNT1 fibrils are enriched in cross β-sheets. Sequence alignment revealed conservation of the CAR across the Henipavirus genus and enabled the identification of a hitherto never reported pro-amyloidogenic motif. The ability to form fibrils was experimentally shown to be a common property shared by Henipavirus PNT1 proteins. Overall, this study sheds light on the molecular mechanisms underlying WHeV fibrillation and calls for future studies aimed at exploring the relevance of the newly identified pro-amyloidogenic motif as a valuable target for antiviral approaches.

Comprehensive amino acid composition analysis of seed storage proteins of cereals and legumes: identification and understanding of intrinsically disordered and allergenic peptides

The seed storage proteins of cereal and legumes are the primary source of amino acids which are required for sustaining the nitrogen and carbon demands during germination and growth. Humans derive most of their dietary proteins from storage proteins in form of a wide variety of foods, for consumption. The amino acid content of most of these proteins is biased and the need for this biasness is not understood. The high abundance of proline, glutamine, and cysteine in cereals makes the gluten fraction viscoelastic. The cereal proteins have less charge and legume proteins have more charge on them. Their non-polar amino acid distribution has large variations. These characteristics are strongly responsible for the partial and complete unfolding of several domains of the storage proteins. Many of the storage proteins share a highly conserved structural feature within the cupin superfamily spread across all kingdoms of life. The intrinsically disordered viscoelastic proteins help in making dough which is vital for the quality of bread. Unfolded regions harbor more immunogenic sequences and cause food-related allergies and intolerance. We have discussed these properties in terms of comparison of cereal and legume storage protein sequences and allergy. Our study supports the findings that large disordered regions contain allergen-representative peptides. Interestingly, a high number of allergen-representative peptides were cleavable by digestive enzymes. Furthermore, unfolded storage proteins mimic microbial immunogens to induce a memory immune response. Results findings can be used to guide the understanding of immunological characteristics of storage proteins and may assist in treatment decisions for food allergy.

Structure-resolved dynamics of type 2M von Willebrand disease

BACKGROUND

Genetically determined amino acid substitutions in the platelet adhesive A1 domain alter von Willebrand factor's (VWF) platelet agglutination competence, resulting in both gain- (type 2B) and loss-of-function (type 2M) phenotypes of von Willebrand disease. Prior studies of variants in both phenotypes revealed defects in secondary structure that altered stability and folding of the domain. An intriguing observation was that loss of function arose from both misfolding of A1 and, in a few cases, hyperstabilization of the native structure.

OBJECTIVES

To fully understand the 2M phenotype, we thoroughly investigated the structure/function relationships of 15 additional type 2M variants and 2 polymorphisms in the A1 domain.

METHODS

These variants were characterized using circular dichroism, fluorescence, calorimetry, hydrogen-deuterium exchange mass spectrometry, surface plasmon resonance, and platelet adhesion under shear flow.

RESULTS

Six variants were natively folded, with 4 being hyperstabilized. Nine variants disordered A1, causing a loss in α-helical structure and unfolding enthalpy. GPIbα binding affinity and platelet adhesion dynamics were highly correlated to helical structure. Hydrogen-deuterium exchange resolved specific C-terminal secondary structure elements that differentially diminish the GPIbα binding affinity of A1. These localized structural perturbations were highly correlated to GPIbα binding affinity and shear-dependent platelet adhesion.

CONCLUSION

While hyperstabilized dynamics in A1 do impair stable platelet attachment to VWF under flow, variant-induced localized disorder in specific regions of the domain misfolds A1 and abrogates platelet adhesion. These 2 opposing conformational properties represent 2 structural classes of VWF that drive the loss-of-function phenotype that is type 2M von Willebrand disease.

Active telomere elongation by a subclass of cancer-associated POT1 mutations

Mutations in the shelterin protein POT1 are associated with diverse cancers and thought to drive carcinogenesis by impairing POT1's suppression of aberrant telomere elongation. To classify clinical variants of uncertain significance (VUSs) and identify cancer-driving loss-of-function mutations, we developed a locally haploid human stem cell system to evaluate >1900 POT1 mutations, including >600 VUSs. Unexpectedly, many validated familial cancer-associated POT1 (caPOT1) mutations are haplosufficient for cellular viability, indicating that some pathogenic alleles do not act through a loss-of-function mechanism. Instead, POT1's DNA damage response suppression and telomere length control are genetically separable. ATR inhibition enables isolation of frameshift mutants, demonstrating that the only essential function of POT1 is to repress ATR. Furthermore, comparison of caPOT1 and frameshift alleles reveals a class of caPOT1 mutations that elongate telomeres more rapidly than full loss-of-function alleles. This telomere length-promoting activity is independent from POT1's role in overhang sequestration and fill-in synthesis.

AVPpred-BWR: antiviral peptides prediction via biological words representation

MOTIVATION

Antiviral peptides (AVPs) are short chains of amino acids, showing great potential as antiviral drugs. The traditional wisdom (e.g. wet experiments) for identifying the AVPs is time-consuming and laborious, while cutting-edge computational methods are less accurate to predict them.

RESULTS

In this article, we propose an AVPs prediction model via biological words representation, dubbed AVPpred-BWR. Based on the fact that the secondary structures of AVPs mainly consist of α-helix and loop, we explore the biological words of 1mer (corresponding to loops) and 4mer (4 continuous residues, corresponding to α-helix). That is, the peptides sequences are decomposed into biological words, and then the concealed sequential information is represented by training the Word2Vec models. Moreover, in order to extract multi-scale features, we leverage a CNN-Transformer framework to process the embeddings of 1mer and 4mer generated by Word2Vec models. To the best of our knowledge, this is the first time to realize the word segmentation of protein primary structure sequences based on the regularity of protein secondary structure. AVPpred-BWR illustrates clear improvements over its competitors on the independent test set (e.g. improvements of 4.6% and 11.0% for AUROC and MCC, respectively, compared to UniDL4BioPep).

AVAILABILITY AND IMPLEMENTATION

AVPpred-BWR is publicly available at: https://github.com/zyweizm/AVPpred-BWR or https://zenodo.org/records/14880447 (doi: 10.5281/zenodo.14880447).

The E3 ubiquitin ligase MGRN1 targets melanocortin receptors MC1R and MC4R via interactions with transmembrane adapters

E3 ubiquitin ligases play a crucial role in modulating receptor stability and signaling at the cell surface, yet the mechanisms governing their substrate specificity remain incompletely understood. Mahogunin Ring Finger 1 (MGRN1) is a membrane-tethered E3 ligase that fine-tunes signaling sensitivity by targeting surface receptors for ubiquitination and degradation. Unlike cytosolic E3 ligases, membrane-tethered E3s require transmembrane adapters to selectively recognize and regulate surface receptors, yet few such ligases have been studied in detail. While MGRN1 is known to regulate the receptor Smoothened (SMO) within the Hedgehog pathway through its interaction with the transmembrane adapter Multiple Epidermal Growth Factor-like 8 (MEGF8), the broader scope of its regulatory network has been speculative. Here, we identify Attractin (ATRN) and Attractin-like 1 (ATRNL1) as additional transmembrane adapters that recruit MGRN1 and regulate cell surface receptor turnover. Through co-immunoprecipitation, we show that ATRN and ATRNL1 likely interact with the RING domain of MGRN1. Functional assays reveal that MGRN1 requires these transmembrane adapters to ubiquitinate and degrade the melanocortin receptors MC1R and MC4R, in a process analogous to its regulation of SMO. Loss of MGRN1 leads to increased surface and ciliary localization of MC4R in fibroblasts and elevated MC1R levels in melanocytes, with the latter resulting in enhanced eumelanin production. These findings expand the repertoire of MGRN1-regulated receptors and provide new insight into a shared mechanism by which membrane-tethered E3 ligases utilize transmembrane adapters to dictate substrate receptor specificity. By elucidating how MGRN1 selectively engages with surface receptors, this work establishes a broader framework for understanding how this unique class of E3 ligases fine-tunes receptor homeostasis and signaling output.

The Arabidopsis thaliana core splicing factor PORCUPINE/SmE1 requires intron-mediated expression

Plants are prone to genome duplications and tend to preserve multiple gene copies. This is also the case for the genes encoding the Sm proteins of Arabidopsis thaliana (L). The Sm proteins are best known for their roles in RNA processing such as pre-mRNA splicing and nonsense-mediated mRNA decay. In this study, we have taken a closer look at the phylogeny and differential regulation of the SmE-coding genes found in A. thaliana, PCP/SmE1, best known for its cold-sensitive phenotype, and its paralog, PCPL/SmE2. The phylogeny of the PCP homologs in the green lineage shows that SmE duplications happened multiple times independently in different plant clades and that the duplication that gave rise to PCP and PCPL occurred only in the Brassicaceae family. Our analysis revealed that A. thaliana PCP and PCPL proteins, which only differ in two amino acids, exhibit a very high level of functional conservation and can perform the same function in the cell. However, our results indicate that PCP is the prevailing copy of the two SmE genes in A. thaliana as it is more highly expressed and that the main difference between PCP and PCPL resides in their transcriptional regulation, which is strongly linked to intronic sequences. Our results provide insight into the complex mechanisms that underlie the differentiation of the paralogous gene expression as an adaptation to stress.

Assembly Formation of P65 Protein, Featured by an Intrinsically Disordered Region Involved in Gliding Machinery of Mycoplasma pneumoniae

Mycoplasma pneumoniae is a human pathogen that glides on host cell surfaces by a repeated catch and release mechanism using sialylated oligosaccharides. At a pole, this organism forms a protrusion called an attachment organelle composed of surface structures, including an adhesin complex and an internal core structure. To clarify the structure and function of the attachment organelle, we focused on a core component, P65, which is essential for stabilization of the adjacent surface and core proteins P30 and HMW2, respectively. Analysis of its amino acid sequence (405 residues) suggested that P65 contains an intrinsically disordered region (residues 1-217) and coiled-coil regions (residues 226-247, 255-283, and 286-320). Four protein fragments and the full-length P65 were analyzed by size exclusion chromatography, analytical centrifugation, circular dichroism spectroscopy, small-angle X-ray scattering, limited proteolysis, and negative staining electron microscopy. The results showed that P65 formed a multimer composed of a central globule with 30 and 23 nm axes and four to six projections 14 nm in length. Our data suggest that the C-terminal region of P65 is responsible for multimerization, while the intrinsically disordered N-terminal region forms a filament. These assignments and roles of P65 in the attachment organelle are discussed.

The Structural Permissiveness of Triosephosphate Isomerase (TpiA) of Escherichia coli

Triosephosphate isomerase (TpiA) is widely regarded as an example of an optimally evolved enzyme due to its essential role in biological systems, its structural conservation, and its near-perfect kinetic parameters. In this study, we investigated the structural robustness of the archetypal TpiA variant from Escherichia coli using an in vitro 5-amino acid linker scanning method. The resulting library was introduced into a tpiA mutant strain for functional complementation. From this library, 16 TpiA variants that were phenotypically indistinguishable from the wild-type enzyme were selected for further analysis. Although all variants retained enzymatic activities within the wild-type range, several insertions were found in highly structured protein domains where the linker was expected to cause significant structural perturbations. Despite these potentially disruptive additions, the enzymes maintained their activity even when expressed in a dnaK mutant, suggesting that chaperones did not compensate for structural abnormalities in vivo. Additionally, when these mutant TpiA variants were produced using an in vitro transcription/translation system, they exhibited enzymatic activity comparable to, and in some cases exceeding, that of the non-mutated enzyme. AlphaFold2 exposed that insertions reconstructed the local architecture of the nearby amino acid sequences. The evolutionary implications of this remarkable structural resilience are discussed.

Flocculation Mechanisms in Brettanomyces bruxellensis: Influence of ethanol and sulfur dioxide on FLO gene expression

The mechanisms underlying flocculation in Brettanomyces bruxellensis, unlike the well-characterized FLO-family gene regulation in Saccharomyces cerevisiae, remain largely unexplored. This study investigates the flocculant phenotypes of 99 B. bruxellensis strains, revealing that only a minority exhibits this clumping behavior and confirms its strain-dependent attitude. Focusing on two strains, CBS2499 (flocculant) and UMY321 (non-flocculant), genetic analysis uncovered polymorphisms and distinct allelic heterozygosity in the FLO1 and FLO11 genes, potentially linked to the phenotypic differences. To further examine these traits, Response Surface Methodology (RSM) was used to simulate oenological conditions, testing the impact of pH, ethanol, and sulfur dioxide (SO₂) levels on flocculation and gene expression. The findings revealed that environmental stressors, especially ethanol and SO₂, significantly increase the expression of FLO1 and FLO11 in CBS2499, indicating a regulatory role in flocculation under stress. These insights broaden our understanding of stress adaptation in B. bruxellensis, especially its survival strategies in wine environments. By elucidating factors influencing flocculation, this study contributes valuable knowledge for managing B. bruxellensis spoilage, potentially aiding in the development of targeted approaches to reduce its impact on wine quality.

Lineage-Specific Class-A GPCR Dynamics Reflect Diverse Chemosensory Adaptations in Lophotrochozoa

Sensing external chemosensory cues via Class-A G protein-coupled receptors (GPCRs) is crucial for a multitude of behavioral and biological functions, influencing animal evolution and ecological adaptations. While extensively studied in vertebrates and echinoderms, the role of GPCR-mediated chemoreception in major protostome clades like Lophotrochozoa remains obscure despite their remarkable ecological adaptations across diverse aquatic and terrestrial environments. Utilizing 238 lophotrochozoan genomes across eight phyla, we conducted a large-scale comparative genomics analysis to identify lineage-specific expansions of Class-A GPCR subsets that are likely adapted for chemoreception. Using phylogeny and orthology-inference-based clustering, we distinguished these expansions from conserved orthogroups of prospective endogenous ligand-binding Class-A GPCR subsets. Across phyla, lineage-specific expansions correlated with adaptations to various habitats, ecological niches, and lifestyles, while the influence of whole-genome duplications in driving these lineage-specific expansions appeared to be less significant. Species adapted to various coastal, freshwater, and terrestrial habitats across several classes of Mollusca, Annelida, and other analyzed phyla exhibit large and diverse lineage-specific expansions, while adaptations to extreme deep-sea environments, parasitic lifestyles, sessile behaviors, or alternative chemosensory mechanisms consistently exhibit reductions. Sequence heterogeneity, signatures of positive selection, and conformational flexibility in ligand-binding pockets further highlighted adaptations to environmental signals. In summary, the evolutionary dynamics of Class-A GPCRs in lophotrochozoans reveal a widespread pattern of lineage-specific expansions driven by adaptations for chemoreception across diverse environmental niches, mirroring the trends and prominent roles seen in deuterostome lineages. The comprehensive datasets spanning numerous genomes offer a valuable foundation for advancing GPCR-mediated chemoreception studies in Lophotrochozoa.

CCDC134 controls TLR biogenesis through the ER chaperone Gp96

Toll-like receptors (TLRs) are central to initiate immune responses against invading pathogens. To ensure host defense while avoiding aberrant activation leading to pathogenic inflammation and autoimmune diseases, TLRs are tightly controlled by multilevel regulatory mechanisms. Through a loss-of-function genetic screen in a reporter cell line engineered to undergo cell death upon TLR7-induced IRF5 activation, we identified here CCDC134 as an essential factor for TLR responses. CCDC134 deficiency impaired endolysosomal TLR-induced NF-κB, MAPK, and IRF5 activation, as well as downstream production of proinflammatory cytokines and type I interferons. We further demonstrated that CCDC134 is an endoplasmic reticulum (ER)-resident interactor of Gp96 (HSP90B1/Grp94), an ER chaperone essential for folding and trafficking of plasma membrane and endolysosomal TLRs. CCDC134 controlled Gp96 stability as its loss led to Gp96 hyperglycosylation and ER-associated protein degradation (ERAD)-mediated clearance. Accordingly, CCDC134 deficiency impaired the folding, maturation, and trafficking of TLRs, resulting in blunted inflammatory responses upon stimulation. Altogether, this study reveals CCDC134 as a central regulator of the chaperone Gp96, thereby controlling TLR biogenesis and responses.

The juxtamembrane sequence of small ankyrin 1 mediates the binding of its cytoplasmic domain to SERCA1 and is required for inhibitory activity

Sarcoplasmic/endoplasmic reticulum Ca2+-ATPase1 (SERCA1) is responsible for the clearance of cytosolic Ca2+ in skeletal muscle. Due to its vital importance in regulating Ca2+ homeostasis, the regulation of SERCA1 has been intensively studied. Small ankyrin 1 (sAnk1, Ank1.5), a 17 kDa muscle-specific isoform of ANK1, binds to SERCA1 directly via both its transmembrane and cytoplasmic domains and inhibits SERCA1's ATPase activity. Here, we characterize the interaction between the cytoplasmic domain of sAnk1 (sAnk1(29-155)) and SERCA1. The binding affinity for sAnk1 (29-155) to SERCA1 was 444 nM by blot overlay, about 7-fold weaker than the binding of sAnk1(29-155) to obscurin, a giant protein of the muscle cytoskeleton. Site-directed mutagenesis identified K38, H39, and H41, in the juxtamembrane region, as residues likely to mediate binding to SERCA1. These residues are not required for obscurin binding. Residues R64-K73, which do contribute to obscurin binding, are also required for binding to SERCA1, but only the hydrophobic residues in this sequence are required, not the positively charged residues necessary for obscurin binding. Circular dichroism analysis of sAnk1(29-155) indicates that most mutants show significant structural changes, with the exception of those containing alanines in place of K38, H39 and H41. Although the cytoplasmic domain of sAnk1 does not inhibit SERCA1's Ca2+-ATPase activity, with or without mutations in the juxtamembrane sequence, the inhibitory activity of full-length sAnk1 requires the WT juxtamembrane sequence. We used these data to model sAnk1 and the sAnk1-SERCA1 complex. Our results suggest that, in addition to its transmembrane domain, sAnk1 uses its juxtamembrane sequence and perhaps part of its obscurin binding site to bind to SERCA1, and that this binding contributes to their robust association in situ, as well as regulation of SERCA1's activity.

MEDIATOR15 destabilizes DELLA protein to promote gibberellin-mediated plant development

Mediator, a transcriptional coactivator, regulates plant growth and development by interacting with various transcriptional regulators. MEDIATOR15 (MED15) is a subunit in the Mediator complex potentially involved in developmental control. To uncover molecular functions of Arabidopsis MED15 in development, we searched for its interactors. MED15 was found to interact with DELLA proteins, which negatively regulate gibberellic acid (GA) signaling and positively regulate GA biosynthesis. Mutants and overexpressors of MED15 exhibited multiple GA-related growth phenotypes, which resembled the phenotypes of the DELLA overexpressor and mutant, respectively. Consistent with this observation, DELLA protein levels were inversely correlated with MED15 protein levels, suggesting that MED15 activates GA signaling through DELLA degradation. MED15 was required not only for DELLA-mediated induction of GA-biosynthesis gene expression but also for GA-mediated degradation of DELLA. Therefore, MED15 facilitates DELLA destruction not only by promoting GA biosynthesis but also by accelerating DELLA turnover. Furthermore, MED15-mediated GA signaling was required for timely developmental responses to dark and warm conditions. Our results provide insight into developmental control by Mediator via precise regulation of DELLA stability. These findings are potentially useful for the generation of new crop cultivars with ideal body architecture.

Cargo hitchhiking autophagy - a hybrid autophagy pathway utilized in yeast

Macroautophagy is a catabolic process that maintains cellular homeostasis by recycling intracellular material through the use of double-membrane vesicles called autophagosomes. In turn, autophagosomes fuse with vacuoles (in yeast and plants) or lysosomes (in metazoans), where resident hydrolases degrade the cargo. Given the conservation of autophagy, Saccharomyces cerevisiae is a valuable model organism for deciphering molecular details that define macroautophagy pathways. In yeast, macroautophagic pathways fall into two subclasses: selective and nonselective (bulk) autophagy. Bulk autophagy is predominantly upregulated following TORC1 inhibition, triggered by nutrient stress, and degrades superfluous random cytosolic proteins and organelles. In contrast, selective autophagy pathways maintain cellular homeostasis when TORC1 is active by degrading damaged organelles and dysfunctional proteins. Here, selective autophagy receptors mediate cargo delivery to the vacuole. Now, two groups have discovered a new hybrid autophagy mechanism, coined cargo hitchhiking autophagy (CHA), that uses autophagic receptor proteins to deliver selected cargo to phagophores built in response to nutrient stress for the random destruction of cytosolic contents. In CHA, various autophagic receptors link their cargos to lipidated Atg8, located on growing phagophores. In addition, the sorting nexin heterodimer Snx4-Atg20 assists in the degradation of cargo during CHA, possibly by aiding the delivery of cytoplasmic cargos to phagophores and/or by delaying the closure of expanding phagophores. This review will outline this new mechanism, also known as Snx4-assisted autophagy, that degrades an assortment of cargos in yeast, including transcription factors, glycogen, and a subset of ribosomal proteins.

A defining member of the new cysteine-cradle family is an aECM protein signalling skin damage in C. elegans

Apical extracellular matrices (aECMs) act as crucial barriers, and communicate with the epidermis to trigger protective responses following injury or infection. In Caenorhabditis elegans, the skin aECM, the cuticle, is produced by the epidermis and is decorated with periodic circumferential furrows. We previously showed that mutants lacking cuticle furrows exhibit persistent immune activation (PIA), providing a valuable model to study the link between cuticle damage and immune response. In a genetic suppressor screen, we identified spia-1 as a key gene downstream of furrow collagens and upstream of immune signalling. spia-1 expression oscillates during larval development, peaking between each moult together with patterning cuticular components. It encodes a secreted protein that localises to furrows. SPIA-1 shares a novel cysteine-cradle domain with other aECM proteins. SPIA-1 mediates immune activation in response to furrow loss and is proposed to act as an extracellular signal activator of cuticle damage. This research provides a molecular insight into intricate interplay between cuticle integrity and epidermal immune activation in C. elegans.

Sporophyte-directed gametogenesis in Arabidopsis

Plants alternate between diploid sporophyte and haploid gametophyte generations1. In mosses, which retain features of ancestral land plants, the gametophyte is dominant and has an independent existence. However, in flowering plants the gametophyte has undergone evolutionary reduction to just a few cells enclosed within the sporophyte. The gametophyte is thought to retain genetic control of its development even after reduction2. Here we show that male gametophyte development in Arabidopsis, long considered to be autonomous, is also under genetic control of the sporophyte via a repressive mechanism that includes large-scale regulation of protein turnover. We identify an Arabidopsis gene SHUKR as an inhibitor of male gametic gene expression. SHUKR is unrelated to proteins of known function and acts sporophytically in meiosis to control gametophyte development by negatively regulating expression of a large set of genes specific to postmeiotic gametogenesis. This control emerged late in evolution as SHUKR homologues are found only in eudicots. We show that SHUKR is rapidly evolving under positive selection, suggesting that variation in control of protein turnover during male gametogenesis has played an important role in evolution within eudicots.

Aspirin-responsive gene switch regulating therapeutic protein expression

Current small-molecule-regulated synthetic gene switches face clinical limitations such as cytotoxicity, long-term side-effects and metabolic disturbances. Here, we describe an advanced synthetic platform inducible by risk-free input medication (ASPIRIN), which is activated by acetylsalicylic acid (ASA/aspirin), a multifunctional drug with pain-relieving, anti-inflammatory, and cardiovascular benefits. To construct ASPIRIN, we repurpose plant salicylic acid receptors NPR1 and NPR4. Through domain truncations and high-throughput mutant library screening, we enhance their ASA sensitivity. Optimized NPR1 fused with a membrane-tethering myristoylation signal (Myr-NPR1) forms a complex with NPR4, which is fused with a DNA binding domain (VanR) and a transactivation domain (VP16). ASA induces dissociation of the Myr-NPR1/NPR4-VanR-VP16 complex, allowing nuclear translocation of NPR4-VanR-VP16 to activate VanR-operator-controlled gene expression. In male diabetic mice implanted with microencapsulated ASPIRIN-engineered cells, ASA regulates insulin expression, restores normoglycemia, alleviates pain and reduces biomarkers of diabetic neuropathy and inflammation. We envision this system will pave the way for aspirin-based combination gene therapies.

Partitioning of a 2-bit hash function across 66 communicating cells

Powerful distributed computing can be achieved by communicating cells that individually perform simple operations. Here, we report design software to divide a large genetic circuit across cells as well as the genetic parts to implement the subcircuits in their genomes. These tools were demonstrated using a 2-bit version of the MD5 hashing algorithm, which is an early predecessor to the cryptographic functions underlying cryptocurrency. One iteration requires 110 logic gates, which were partitioned across 66 Escherichia coli strains, requiring the introduction of a total of 1.1 Mb of recombinant DNA into their genomes. The strains were individually experimentally verified to integrate their assigned input signals, process this information correctly and propagate the result to the cell in the next layer. This work demonstrates the potential to obtain programable control of multicellular biological processes.

Conservation of OFD1 Protein Motifs: Implications for Discovery of Novel Interactors and the OFD1 Function

OFD1 is a protein involved in many cellular processes, including cilia biogenesis, mitotic spindle assembly, translation, autophagy and the repair of double-strand DNA breaks. Despite many potential interactors identified in high-throughput studies, only a few have been directly confirmed with their binding sites identified. We performed an analysis of the evolutionary conservation of the OFD1 sequence in three clades: 80 Tetrapoda, 144 Vertebrata or 26 Animalia species, and identified 59 protein-binding motifs localized in the OFD1 regions conserved in various clades. Our results indicate that OFD1 contains 14 potential post-translational modification (PTM) sites targeted by at least eight protein kinases, seven motifs bound by proteins recognizing phosphorylated aa residues and a binding site for phosphatase 2A. Moreover, OFD1 harbors both a motif that enables its phosphorylation by mitogen-activated protein kinases (MAPKs) and a specific docking site for these proteins. Generally, our results suggest that OFD1 forms a scaffold for interaction with many proteins and is tightly regulated by PTMs and ligands. Future research on OFD1 should focus on the regulation of OFD1 function and localization.

Elucidating assembly and function of VirB8 cell wall subunits refines the DNA translocation model in Gram-positive T4SSs

Bacterial type IV secretion systems (T4SSs) are widespread nanomachines specialized in the transport across the cell envelope of various types of molecules including mobile genetic elements during conjugation. Despite their prevalence in Gram-positive bacteria, including relevant pathogens, their assembly and functioning remain unknown. This study addresses these gaps by investigating VirB8 proteins, known to be central components of conjugative T4SSs in Gram-positive bacteria. However, the functional packing and precise role of VirB8 in T4SSs biology remain undefined. Our findings elucidate the nature of VirB8 proteins as cell wall components, where they multimerize and exhibit a conserved assembly pattern, distinct from VirB8 in Gram-negative bacteria. We also demonstrate that VirB8 proteins interact with other T4SS subunits and DNA, indicating their pivotal role in the building of the DNA translocation channel across the cell wall. We lastly propose a distinct architecture for conjugative T4SSs in Gram-positive bacteria compared to their Gram-negative counterparts, possibly attributed to the differences in the cell wall structure.

AlphaFold 2, but not AlphaFold 3, predicts confident but unrealistic β-solenoid structures for repeat proteins

AlphaFold 2 (AF2) has revolutionised protein structure prediction but, like any new tool, its performance on specific classes of targets, especially those potentially under-represented in its training data, merits attention. Prompted by a highly confident prediction for a biologically meaningless, randomly permuted repeat sequence, we assessed AF2 performance on sequences composed of perfect repeats of random sequences of different lengths. AF2 frequently folds such sequences into β-solenoids which, while ascribed high confidence, contain unusual and implausible features such as internally stacked and uncompensated charged residues. A number of sequences confidently predicted as β-solenoids are predicted by other advanced methods as intrinsically disordered. The instability of some predictions is demonstrated by molecular dynamics. Importantly, other deep learning-based structure prediction tools predict different structures or β-solenoids with much lower confidence suggesting that AF2 alone has an unreasonable tendency to predict confident but unrealistic β-solenoids for perfect repeat sequences. The potential implications for structure prediction of natural (near-)perfect sequence repeat proteins are also explored.

Computational epitope-based vaccine design with bioinformatics approach; a review

The significance of vaccine development has gained heightened importance in light of the COVID-19 pandemic. In such critical circumstances, global citizens anticipate researchers in this field to swiftly identify a vaccine candidate to combat the pandemic's root cause. It is widely recognized that the vaccine design process is traditionally both time-consuming and costly. However, a specialized subfield within bioinformatics, known as "multi-epitope vaccine design" or "reverse vaccinology," has significantly decreased the time and costs of the vaccine design process. The methodology reverses itself in this subfield and finds a potential vaccine candidate by analyzing the pathogen's genome. Leveraging the tools available in this domain, we strive to pinpoint the most suitable antigen for crafting a vaccine against our target. Once the optimal antigen is identified, the next step involves uncovering epitopes within this antigen. The immune system recognizes particular areas of an antigen as epitopes. By characterizing these crucial segments, we gain the opportunity to design a vaccine centered around these epitopes. Subsequently, after identifying and assembling the vital epitopes with the assistance of linkers and adjuvants, our vaccine candidate can be formulated. Finally, employing computational techniques, we can thoroughly evaluate the designed vaccine. This review article comprehensively covers the entire multi-epitope vaccine development process, starting from obtaining the pathogen's genome to identifying the relevant vaccine candidate and concluding with an evaluation. Furthermore, we will delve into the essential tools needed at each stage, comparing and introducing them.

The Expression, Purification, Spectroscopic Characterization, and Membrane Topology Classification of KCNE4 from Recombinant E. coli

Members of the KCNE family are accessory subunits that modulate voltage-gated potassium channels. One member, KCNE4, has been shown to inhibit the potassium ion current in these channels. However, little is known about the structure, dynamics, and mode of inhibition of KCNE4, likely due to challenges in overexpressing and purifying the protein. In this study, an alternative expression and purification protocol has been developed and validated to obtain overexpressed KCNE4 for in vitro studies. This protocol was validated through SDS-PAGE, CW-EPR, CW-EPR power saturation, and CD experiments. The SDS-PAGE and CD data reveal that this protocol produces relatively pure and properly folded KCNE4 in large quantities at a lower cost. The CW-EPR and EPR power saturation spectra show that KCNE4 consists of extracellular, transmembrane, and intracellular regions. Together, these techniques indicate that this alternative protocol produces structurally and dynamically native KCNE4 without the need for mammalian cell lines. This study provides guidance for characterizing the structure and dynamics of KCNE4 in a lipid bilayer environment.

Defining ortholog-specific UHRF1 inhibition by STELLA for cancer therapy

UHRF1 maintains DNA methylation by recruiting DNA methyltransferases to chromatin. In mouse, these dynamics are potently antagonized by a natural UHRF1 inhibitory protein STELLA, while the comparable effects of its human ortholog are insufficiently characterized, especially in cancer cells. Herein, we demonstrate that human STELLA (hSTELLA) is inadequate, while mouse STELLA (mSTELLA) is fully proficient in inhibiting the abnormal DNA methylation and oncogenic functions of UHRF1 in human cancer cells. Structural studies reveal a region of low sequence homology between these STELLA orthologs that allows mSTELLA but not hSTELLA to bind tightly and cooperatively to the essential histone-binding, linked tandem Tudor domain and plant homeodomain (TTD-PHD) of UHRF1, thus mediating ortholog-specific UHRF1 inhibition. For translating these findings to cancer therapy, we use a lipid nanoparticle (LNP)-mediated mRNA delivery approach in which the short mSTELLA, but not hSTELLA regions are required to reverse cancer-specific DNA hypermethylation and impair colorectal cancer tumorigenicity.

Using environment-sensitive tetramethylated thiophene-BODIPY fluorophores in DNA probes for studying effector-induced conformational changes of protein-DNA complexes

The LutR protein represses the transcription of genes encoding enzymes for the utilization of l-lactate in Bacillus subtilis through binding to a specific DNA region. In this study, we employed oligonucleotide probes modified by viscosity-sensitive tetramethylated thiophene-BODIPY fluorophores to investigate the impact of selected metabolites on the LutR-DNA complex. Our goal was to identify the effector molecule whose binding alters the protein-DNA affinity, thereby enabling gene transcription. The designed DNA probes exhibited distinctive responses to the binding and release of the protein, characterized by significant alterations in fluorescence lifetime. Through this method, we have identified l-lactate as the sole metabolite exerting a substantial modulating effect on the protein-DNA interaction and thus confirmed its role as an effector molecule. Moreover, we showed that our approach was able to follow conformation changes affecting affinity, which were not captured by other methods commonly used to study the protein-DNA interaction, such as electro-mobility shift assays and florescence anisotropy binding studies. This work underlines the potential of environment-sensitive fluorophore-linked nucleotide modifications, i.e. dCTBdp, for studying the dynamics and subtle changes of protein-DNA interactions.

Recent Advances in Computational Prediction of Secondary and Supersecondary Structures from Protein Sequences

The secondary structures (SSs) and supersecondary structures (SSSs) underlie the three-dimensional structure of proteins. Prediction of the SSs and SSSs from protein sequences enjoys high levels of use and finds numerous applications in the development of a broad range of other bioinformatics tools. Numerous sequence-based predictors of SS and SSS were developed and published in recent years. We survey and analyze 45 SS predictors that were released since 2018, focusing on their inputs, predictive models, scope of their prediction, and availability. We also review 32 sequence-based SSS predictors, which primarily focus on predicting coiled coils and beta-hairpins and which include five methods that were published since 2018. Substantial majority of these predictive tools rely on machine learning models, including a variety of deep neural network architectures. They also frequently use evolutionary sequence profiles. We discuss details of several modern SS and SSS predictors that are currently available to the users and which were published in higher impact venues.

Interaction of cardiac leiomodin with the native cardiac thin filament

Every heartbeat depends on cyclical contraction-relaxation produced by the interactions between myosin-containing thick and actin-based thin filaments (TFs) arranged into a crystalline-like lattice in the cardiac sarcomere. Therefore, the maintenance of thin filament length is crucial for myocardium function. The thin filament is comprised of an actin backbone, the regulatory troponin complex and tropomyosin that controls interactions between thick and thin filaments. Thin filament length is controlled by the tropomodulin family of proteins; tropomodulin caps pointed ends of thin filaments, and leiomodin (Lmod) promotes elongation of thin filaments by a "leaky-cap" mechanism. The broader distribution of Lmod on the thin filament implied to the possibility of its interaction with the sides of thin filaments. Here, we use biochemical and structural approaches to show that cardiac Lmod (Lmod2) binds to a specific region on the native cardiac thin filament in a Ca2+-dependent manner. We demonstrate that Lmod2's unique C-terminal extension is required for binding to the thin filament actin backbone and suggest that interactions with the troponin complex assist Lmod2's localization on the surface of thin filaments. We propose that Lmod2 regulates the length of cardiac thin filaments in a working myocardium by protecting newly formed thin filament units during systole and promoting actin polymerization at thin filament pointed ends during diastole.

The Iconic α-Helix: From Pauling to the Present

The protein folding problem dates back to Pauling's insights almost a century ago, but the first venture into actual protein structure was the Pauling-Corey-Brandson α-helix in 1951, a proposed model that was confirmed almost immediately using X-ray crystallography. Many subsequent efforts to predict protein helices from the amino acid sequence met with only partial success, as discussed here. Surprisingly, in 2021, these efforts were superseded by deep-learning artificial intelligence, especially AlphaFold2, a machine learning program based on neural nets. This approach can predict most protein structures successfully at or near atomic resolution. Deservedly, deep-learning artificial intelligence was named Science magazine's 2021 "breakthrough of the year." Today, ~200 million predicted protein structures can be downloaded from the AlphaFold2 Protein Structure Database. Deep learning represents a deep conundrum because these successfully predicted macromolecular structures are based on methods that are completely devoid of a hypothesis or of any physical chemistry. Perhaps we are now poised to transcend five centuries of reductive science.

From propensities to patterns to principles in protein folding

As proposed here, β-turns play an essential role in protein self-assembly. This compact, four-residue motif affects protein conformation dramatically by reversing the overall chain direction. Turns are the "hinges" in globular proteins. This new proposal broadens a previous hypothesis that globular proteins solve the folding problem in part by filtering conformers with unsatisfied backbone hydrogen bonds, thereby preorganizing the folding population. Recapitulating that hypothesis: unsatisfied conformers would be dramatically destabilizing, shifting the U(nfolded) ⇌ N(ative) equilibrium far to the left. If even a single backbone polar group is satisfied by solvent when unfolded but buried and unsatisfied when folded, that energy penalty alone, approximately +5 kcal/mol, would rival almost the entire free energy of protein stabilization at room temperature. Consequently, globular proteins are built on scaffolds of hydrogen-bonded α-helices and/or strands of β-sheet, motifs that can be extended indefinitely, with intra-segment hydrogen bond partners for their backbone polar groups and without steric clash. Scaffolds foster a protein-wide hydrogen-bonded network, and, of thermodynamic necessity, they self-assemble cooperatively. Unlike elements of repetitive secondary structure, α-helices and β-sheet, a four-residue β-turn has only a single hydrogen bond (from i + 3 → i), not a cooperatively formed assembly of hydrogen bonds. As such, turns can form autonomously and are poised to initiate assembly of scaffold elements by bringing them together in an orientation and registration that promotes cooperative "zipping". The overall effect of this self-assembly mechanism is to induce substantial preorganization in the thermodynamically accessible folding population and, concomitantly, to reduce the folding entropy.

From sequence to function: Exploring biophysical properties of bacteriophage BFK20 lytic transglycosylase domain from the minor tail protein gp15

Bacteriophages have evolved different mechanisms of infection and penetration of bacterial cell walls. In Siphoviridae-like viruses, the inner tail proteins have a pivotal role in these processes and often encode lytic protein domains which increase infection efficiency. A soluble lytic transglycosylase (SLT) domain was identified in the minor tail protein gp15 from the BFK20 bacteriophage. Six fragments containing this SLT domain with adjacent regions of different lengths were cloned, expressed and purified. The biophysical properties of the two best expressing fragments were characterized by nanoDSF and CD spectroscopy, which showed that both fragments had a high refolding ability of 90 %. 3D modeling indicated that the bacteriophage BFK20 SLT domain is structurally similar to lysozyme. The degradation activity of these SLT proteins was evaluated using a lysozyme activity assay. BFK20 might use its transglycosylase activity to allow efficient phage DNA entry into the host cell by degrading bacterial peptidoglycan.

NMR Studies on the Structure of Yeast Sis1 and the Dynamics of Its Interaction with Ssa1-EEVD

HSP70 chaperones play pivotal roles in facilitating protein folding, refolding, and disaggregation through their binding and releasing activities. This intricate process is further supported by J-domain proteins (JDPs), also known as DNAJs or HSP40s, which can be categorized into classes A and B. In yeast, these classes are represented by Ydj1 and Sis1, respectively. While both classes stimulate the ATPase activity of Ssa1 (yeast HSP70) through the J-domain, only class B JDPs possess the unique ability to efficiently stimulate Ssa1 in disaggregation processes. The C-terminal EEVD motif of HSP70 plays a crucial role in mediating these interactions by connecting with both client proteins and JDPs. However, the removal of the EEVD motif disrupts the capacity of HSP70 to associate with class B JDPs, and the intricacies of the interaction between these two proteins remain incompletely understood. We employed NMR spectroscopy to investigate the structure and dynamics of the class B J domain protein (JDP) of S. cerevisiae (Sis1) complexed with an EEVD peptide of Ssa1. Our study is based on the extraordinary 70.5% residue assignment of the full-length (352 residues long) Sis1. Our findings revealed that EEVD binds to two distinct sites within the C-terminal domain I (CTDI) of Sis1, to the J domain and to the GF-rich loop located between the J domain and α-helix 6 (a structure identified by this work). We propose that the interaction between EEVD and Sis1 facilitates the dissociation of α-helix 6, promoting a conformational state that is more favorable for interaction with Ssa1. We also employed α-synuclein as a substrate to investigate the competitive nature between EEVD and the client protein. Our experimental findings provide evidence supporting the interaction of EEVD with the client protein at multiple sites and essential insights into the mechanistic cycle of class B JDPs.

The conformation of FOXM1 homodimers in vivo is crucial for regulating transcriptional activities

Conformational changes in a transcription factor can significantly affect its transcriptional activity. The activated form of the FOXM1 transcription factor regulates the transcriptional network of genes essential for cell cycle progression and carcinogenesis. However, the mechanism and impact of FOXM1 conformational change on its transcriptional activity in vivo throughout the cell cycle progression remain unexplored. Here, we demonstrate that FOXM1 proteins form novel intermolecular homodimerizations in vivo, and these conformational changes in FOXM1 homodimers impact activity during the cell cycle. Specifically, during the G1 phase, FOXM1 undergoes autorepressive homodimerization, wherein the αβα motif in the C-terminal transcriptional activation domain interacts with the ββαβ motif in the N-terminal repression domain, as evidenced by FRET imaging. Phosphorylation of the αβα motif by PLK1 at S715/S724 disrupts ββαβ-αβα hydrophobic interactions, thereby facilitating a conserved αβα motif switch binding partner to the novel intrinsically disordered regions, leading to FOXM1 autostimulatory homodimerization persisting from the S phase to the G2/M phase in vivo. Furthermore, we identified a minimal ββαβ motif peptide that effectively inhibits cancer cell proliferation both in cell culture and in a mouse tumor model, suggesting a promising autorepression approach for targeting FOXM1 in cancer therapy.

A genome-wide screen identifies silencers with distinct chromatin properties and mechanisms of repression

Differential gene transcription enables development and homeostasis in all animals and is regulated by two major classes of distal cis-regulatory DNA elements (CREs): enhancers and silencers. Although enhancers have been thoroughly characterized, the properties and mechanisms of silencers remain largely unknown. By an unbiased genome-wide functional screen in Drosophila melanogaster S2 cells, we discover a class of silencers that bind one of three transcription factors (TFs) and are generally not included in chromatin-defined CRE catalogs as they mostly lack detectable DNA accessibility. The silencer-binding TF CG11247, which we term Saft, safeguards cell fate decisions in vivo and functions via a highly conserved domain we term zinc-finger-associated C-terminal (ZAC) and the corepressor G9a, independently of G9a's H3K9-methyltransferase activity. Overall, our identification of silencers with unexpected properties and mechanisms has important implications for the understanding and future study of repressive CREs, as well as the functional annotation of animal genomes.

In silico design of a novel hybrid epitope-based antigen harboring highly exposed immunogenic peptides of BamA, OmpA, and Omp34 against Acinetobacter baumannii

Acinetobacter baumannii, is among the highest priority bacteria according to the WHO categorization which necessitate the exploration of alternative strategies such as vaccination. OmpA, BamA, and Omp34 are assigned as appropriate antigens to serve in vaccine development against this pathogen. Experimentally validated exposed epitopes of OmpA and Omp34 along with selected exposed epitopes predicted by an integrative in silico approach were represented by the barrel domain of BamA as a scaffold. Among the 8 external loops of BamA, 5 loops were replaced with selected loops of OmpA and Omp34. The designed antigen was analyzed regarding the physicochemical properties, antigenicity, epitope retrieval, topology, structure, and safety. BamA is a two-domain OMP with a 16-stranded barrel in which L4, L6, and L7 were the longest loops of BamA in order. The designed antigen consisted of 478 amino acids with antigen probability of 0.7793. The novel antigen was a 16-stranded barrel. No identical 8-meric peptides were found in the human proteome against the designed antigen sequence. The designed construct was safe regarding the allergenicity, toxicity, and human proteome reactivity. The designed antigen could develop higher protection against A. baumannii in comparison to either OmpA, BamA, or Omp34 alone.

Interactomic Analyses and a Reverse Engineering Study Identify Specific Functional Activities of One-to-One Interactions of the S1 Subunit of the SARS-CoV-2 Spike Protein with the Human Proteome

The S1 subunit of SARS-CoV-2 Spike is crucial for ACE2 recognition and viral entry into human cells. It has been found in the blood of COVID-19 patients and vaccinated individuals. Using BioGRID, I identified 146 significant human proteins that interact with S1. I then created an interactome model that made it easier to study functional activities. Through a reverse engineering approach, 27 specific one-to-one interactions of S1 with the human proteome were selected. S1 interacts in this manner independently from the biological context in which it operates, be it infection or vaccination. Instead, when it works together with viral proteins, they carry out multiple attacks on single human proteins, showing a different functional engagement. The functional implications and tropism of the virus for human organs/tissues were studied using Cytoscape. The nervous system, liver, blood, and lungs are among the most affected. As a single protein, S1 operates in a complex metabolic landscape which includes 2557 Biological Processes (GO), much more than the 1430 terms controlled when operating in a group. A Data Merging approach shows that the total proteins involved by S1 in the cell are over 60,000 with an average involvement per single biological process of 26.19. However, many human proteins become entangled in over 100 different biological activities each. Clustering analysis showed significant activations of many molecular mechanisms, like those related to hepatitis B infections. This suggests a potential involvement in carcinogenesis, based on a viral strategy that uses the ubiquitin system to impair the tumor suppressor and antiviral functions of TP53, as well as the role of RPS27A in protein turnover and cellular stress responses.

A comprehensive overview of recent advances in generative models for antibodies

Therapeutic antibodies are an important class of biopharmaceuticals. With the rapid development of deep learning methods and the increasing amount of antibody data, antibody generative models have made great progress recently. They aim to solve the antibody space searching problems and are widely incorporated into the antibody development process. Therefore, a comprehensive introduction to the development methods in this field is imperative. Here, we collected 34 representative antibody generative models published recently and all generative models can be divided into three categories: sequence-generating models, structure-generating models, and hybrid models, based on their principles and algorithms. We further studied their performance and contributions to antibody sequence prediction, structure optimization, and affinity enhancement. Our manuscript will provide a comprehensive overview of the status of antibody generative models and also offer guidance for selecting different approaches.

SERT-StructNet: Protein secondary structure prediction method based on multi-factor hybrid deep model

Protein secondary structure prediction (PSSP) is a pivotal research endeavour that plays a crucial role in the comprehensive elucidation of protein functions and properties. Current prediction methodologies are focused on deep-learning techniques, particularly focusing on multi-factor features. Diverging from existing approaches, in this study, we placed special emphasis on the effects of amino acid properties and protein secondary structure propensity scores (SSPs) on secondary structure during the meticulous selection of multi-factor features. This differential feature-selection strategy results in a distinctive and effective amalgamation of the sequence and property features. To harness these multi-factor features optimally, we introduced a hybrid deep feature extraction model. The model initially employs mechanisms such as dilated convolution (D-Conv) and a channel attention network (SENet) for local feature extraction and targeted channel enhancement. Subsequently, a combination of recurrent neural network variants (BiGRU and BiLSTM), along with a transformer module, was employed to achieve global bidirectional information consideration and feature enhancement. This approach to multi-factor feature input and multi-level feature processing enabled a comprehensive exploration of intricate associations among amino acid residues in protein sequences, yielding a Q 3 accuracy of 84.9% and an Sov score of 85.1%. The overall performance surpasses that of the comparable methods. This study introduces a novel and efficient method for determining the PSSP domain, which is poised to deepen our understanding of the practical applications of protein molecular structures.

New insights into the functions of ACBD4/5-like proteins using a combined phylogenetic and experimental approach across model organisms

Acyl-CoA binding domain-containing proteins (ACBDs) perform diverse but often uncharacterised functions linked to cellular lipid metabolism. Human ACBD4 and ACBD5 are closely related peroxisomal membrane proteins, involved in tethering of peroxisomes to the ER and capturing fatty acids for peroxisomal β-oxidation. ACBD5 deficiency causes neurological abnormalities including ataxia and white matter disease. Peroxisome-ER contacts depend on an ACBD4/5-FFAT motif, which interacts with ER-resident VAP proteins. As ACBD4/5-like proteins are present in most fungi and all animals, we combined phylogenetic analyses with experimental approaches to improve understanding of their evolution and functions. Notably, all vertebrates exhibit gene sequences for both ACBD4 and ACBD5, while invertebrates and fungi possess only a single ACBD4/5-like protein. Our analyses revealed alterations in domain structure and FFAT sequences, which help understanding functional diversification of ACBD4/5-like proteins. We show that the Drosophila melanogaster ACBD4/5-like protein possesses a functional FFAT motif to tether peroxisomes to the ER via Dm_Vap33. Depletion of Dm_Acbd4/5 caused peroxisome redistribution in wing neurons and reduced life expectancy. In contrast, the ACBD4/5-like protein of the filamentous fungus Ustilago maydis lacks a FFAT motif and does not interact with Um_Vap33. Loss of Um_Acbd4/5 resulted in an accumulation of peroxisomes and early endosomes at the hyphal tip. Moreover, lipid droplet numbers increased, and mitochondrial membrane potential declined, implying altered lipid homeostasis. Our findings reveal differences between tethering and metabolic functions of ACBD4/5-like proteins across evolution, improving our understanding of ACBD4/5 function in health and disease. The need for a unifying nomenclature for ACBD proteins is discussed.

Biophysical Characterization of a Novel Phosphopentomutase from the Hyperthermophilic Archaeon Thermococcus kodakarensis

Phosphopentomutases catalyze the isomerization of ribose 1-phosphate and ribose 5-phosphate. Thermococcus kodakarensis, a hyperthermophilic archaeon, harbors a novel enzyme (PPMTk) that exhibits high homology with phosphohexomutases but has no significant phosphohexomutase activity. Instead, PPMTk catalyzes the interconversion of ribose 1-phosphate and ribose 5-phosphate. Here, we report biophysical analysis, crystallization, and three-dimensional structure determination of PPMTk by X-ray diffraction at 2.39 Å resolution. The solved structure revealed a novel catalytic motif, unique to PPMTk, which makes this enzyme distinct from the homologous counterparts. We postulate that this novel catalytic motif may enable PPMTk to isomerize phosphopentose instead of phosphohexose. To the best of our knowledge, this is the first biophysical and structural analysis of a phosphopentomutase from hyperthermophilic archaea.

Broadly conserved FlgV controls flagellar assembly and Borrelia burgdorferi dissemination in mice

Flagella propel pathogens through their environments, yet are expensive to synthesize and are immunogenic. Thus, complex hierarchical regulatory networks control flagellar gene expression. Spirochetes are highly motile bacteria, but peculiarly, the archetypal flagellar regulator σ28 is absent in the Lyme spirochete Borrelia burgdorferi. Here, we show that gene bb0268 (flgV) in B. burgdorferi, previously and incorrectly annotated to encode the RNA-binding protein Hfq, is instead a structural flagellar component that modulates flagellar assembly. The flgV gene is broadly conserved in the flagellar superoperon alongside σ28 in many Spirochaetae, Firmicutes and other phyla, with distant homologs in Epsilonproteobacteria. We find that B. burgdorferi FlgV is localized within flagellar basal bodies, and strains lacking flgV produce fewer and shorter flagellar filaments and are defective in cell division and motility. During the enzootic cycle, flgV-deficient B. burgdorferi survive and replicate in Ixodes ticks but are attenuated for infection and dissemination in mice. Our work defines infection timepoints when spirochete motility is most crucial and implicates FlgV as a broadly distributed structural flagellar component that modulates flagellar assembly.

Prediction of Protein Secondary Structures Based on Substructural Descriptors of Molecular Fragments

The accurate prediction of secondary structures of proteins (SSPs) is a critical challenge in molecular biology and structural bioinformatics. Despite recent advancements, this task remains complex and demands further exploration. This study presents a novel approach to SSP prediction using atom-centric substructural multilevel neighborhoods of atoms (MNA) descriptors for protein molecular fragments. A dataset comprising over 335,000 SSPs, annotated by the Dictionary of Secondary Structure in Proteins (DSSP) software from 37,000 proteins, was constructed from Protein Data Bank (PDB) records with a resolution of 2 Å or better. Protein fragments were converted into structural formulae using the RDKit Python package and stored in SD files using the MOL V3000 format. Classification sequence-structure-property relationships (SSPR) models were developed with varying levels of MNA descriptors and a Bayesian algorithm implemented in MultiPASS software. The average prediction accuracy (AUC) for eight SSP types, calculated via leave-one-out cross-validation, was 0.902. For independent test sets (ASTRAL and CB513 datasets), the best SSPR models achieved AUC, Q3, and Q8 values of 0.860, 77.32%, 70.92% and 0.889, 78.78%, 74.74%, respectively. Based on the created models, a freely available web application MNA-PSS-Pred was developed.