Molecular insights into titin's A-band

The thick filament-associated A-band region of titin is a highly repetitive component of the titin chain with important scaffolding properties that support thick filament assembly. It also has a demonstrated link to human disease. Despite its functional significance, it remains a largely uncharacterized part of the titin protein. Here, we have performed an analysis of sequence and structure conservation of A-band titin, with emphasis on poly-FnIII tandem components. Specifically, we have applied multi-dimensional sequence pairwise similarity analysis to FnIII domains and complemented this with the crystallographic elucidation of the 3D-structure of the FnIII-triplet A84-A86 from the fourth long super-repeat in the C-zone (C4). Structural models serve here as templates to map sequence conservation onto super-repeat C4, which we show is a prototypical representative of titin's C-zone. This templating identifies positionally conserved residue clusters in C super-repeats with the potential of mediating interactions to thick-filament components. Conservation localizes to two super-repeat positions: Ig domains in position 1 and FnIII domains in position 7. The analysis also allows conclusions to be drawn on the conserved architecture of titin's A-band, as well as revisiting and expanding the evolutionary model of titin's A-band.

AMP-dependent phosphite dehydrogenase, a phosphorylating enzyme in dissimilatory phosphite oxidation

Oxidation of phosphite (HPO32-) to phosphate (HPO42-) releases electrons at a very low redox potential (E0'= -690 mV) which renders phosphite an excellent electron donor for microbial energy metabolism. To date, two pure cultures of strictly anaerobic bacteria have been isolated that run their energy metabolism on the basis of phosphite oxidation, the Gram-negative Desulfotignum phosphitoxidans (DSM 13687) and the Gram-positive Phosphitispora fastidiosa (DSM 112739). Here, we describe the key enzyme for dissimilatory phosphite oxidation in these bacteria. The enzyme catalyzed phosphite oxidation in the presence of adenosine monophosphate (AMP) to form adenosine diphosphate (ADP), with concomitant reduction of oxidized nicotinamide adenine dinucleotide (NAD+) to reduced nicotinamide adenine dinucleotide (NADH). The enzyme of P. fastidiosa was heterologously expressed in Escherichia coli. It has a molecular mass of 35.2 kDa and a high affinity for phosphite and NAD+. Its activity was enhanced more than 100-fold by addition of ADP-consuming adenylate kinase (myokinase) to a maximal activity between 30 and 80 mU x mg protein-1. A similar NAD-dependent enzyme oxidizing phosphite to phosphate with concomitant phosphorylation of AMP to ADP is found in D. phosphitoxidans, but this enzyme could not be heterologously expressed. Based on sequence analysis, these phosphite-oxidizing enzymes are related to nucleotide-diphosphate-sugar epimerases and indeed represent AMP-dependent phosphite dehydrogenases (ApdA). A reaction mechanism is proposed for this unusual type of substrate-level phosphorylation reaction.

Titin UN2A Acts as a Stable, Non-Polymorphic Scaffold in its Binding to CARP

The N2A segment of titin functions as a pivotal hub for signal transduction and interacts with various proteins involved in structural support, chaperone activities, and transcriptional regulation. Notably, the "unique N2A" (UN2A) subdomain has been shown to interact with the stress-regulated cardiac ankyrin repeat protein (CARP), which contributes to the regulation of sarcomeric stiffness. Previously, the UN2A domain's three-dimensional structure was modelled based on its secondary structure content identified by NMR spectroscopy, considering the domain in isolation. In this study, we report experimental long-range distance distributions by electron paramagnetic resonance (EPR) spectroscopy between the three helixes within the UN2A domain linked to the immunoglobulin domain I81 in the presence and absence of CARP. The data confirm the central three-helix bundle fold of UN2A and show that this adopts a compact and stable conformation in absence of CARP. After binding to CARP, no significant conformational change was observed, suggesting that the UN2A domain retains its structure upon binding to CARP thereby, mediating the interaction approximately as a rigid-body.

Crystal structure of a GCN5-related N-acetyltransferase from Lactobacillus curiae

Members of the GCN5-related N-acetyltransferase (GNAT) family are found in all domains of life and are involved in processes ranging from protein synthesis and gene expression to detoxification and virulence. Due to the variety of their macromolecular targets, GNATs are a highly diverse family of proteins. Currently, 3D structures of only a small number of GNAT representatives are available and thus the family remains poorly characterized. Here, the crystal structure of the guanidine riboswitch-associated GNAT from Lactobacillus curiae (LcGNAT) that acetylates canavanine, a structural analogue of arginine with antimetabolite properties, is reported. LcGNAT shares the conserved fold of the members of the GNAT superfamily, but does not contain an N-terminal β0 strand and instead contains a C-terminal β7 strand. Its P-loop, which coordinates the pyrophosphate moiety of the acetyl-coenzyme A cosubstrate, is degenerated. These features are shared with its closest homologues in the polyamine acetyltransferase subclass. Site-directed mutagenesis revealed a central role of the conserved residue Tyr142 in catalysis, as well as the semi-conserved Tyr97 and Glu92, suggesting that despite its individual substrate specificity LcGNAT performs the classical reaction mechanism of this family.

Immunological and Structural Characterization of Titin Main Immunogenic Region; I110 Domain Is the Target of Titin Antibodies in Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune disease caused by antibodies targeting the neuromuscular junction (NJ) of skeletal muscles. The major MG autoantigen is nicotinic acetylcholine receptor. Other autoantigens at the NJ include MuSK, LRP4 and agrin. Autoantibodies to the intra-sarcomeric striated muscle-specific gigantic protein titin, although not directed to the NJ, are invaluable biomarkers for thymoma and MG disease severity. Thymus and thymoma are critical in MG mechanisms and management. Titin autoantibodies bind to a 30 KDa titin segment, the main immunogenic region (MIR), consisting of an Ig-FnIII-FnIII 3-domain tandem, termed I109-I111. In this work, we further resolved the localization of titin epitope(s) to facilitate the development of more specific anti-titin diagnostics. For this, we expressed protein samples corresponding to 8 MIR and non-MIR titin fragments and tested 77 anti-titin sera for antibody binding using ELISA, competition experiments and Western blots. All anti-MIR antibodies were bound exclusively to the central MIR domain, I110, and to its containing titin segments. Most antibodies were bound also to SDS-denatured I110 on Western blots, suggesting that their epitope(s) are non-conformational. No significant difference was observed between thymoma and non-thymoma patients or between early- and late-onset MG. In addition, atomic 3D-structures of the MIR and its subcomponents were elucidated using X-ray crystallography. These immunological and structural data will allow further studies into the atomic determinants underlying titin-based autoimmunity, improved diagnostics and how to eventually treat titin autoimmunity associated co-morbidities.

Guanidino acid hydrolysis by the human enzyme annotated as agmatinase

Guanidino acids such as taurocyamine, guanidinobutyrate, guanidinopropionate, and guanidinoacetate have been detected in humans. However, except for guanidionacetate, which is a precursor of creatine, their metabolism and potential functions remain poorly understood. Agmatine has received considerable attention as a potential neurotransmitter and the human enzyme so far annotated as agmatinase (AGMAT) has been proposed as an important modulator of agmatine levels. However, conclusive evidence for the assigned enzymatic activity is lacking. Here we show that AGMAT hydrolyzed a range of linear guanidino acids but was virtually inactive with agmatine. Structural modelling and direct biochemical assays indicated that two naturally occurring variants differ in their substrate preferences. A negatively charged group in the substrate at the end opposing the guanidine moiety was essential for efficient catalysis, explaining why agmatine was not hydrolyzed. We suggest to rename AGMAT as guanidino acid hydrolase (GDAH). Additionally, we demonstrate that the GDAH substrates taurocyamine, guanidinobutyrate and guanidinopropionate were produced by human glycine amidinotransferase (GATM). The presented findings show for the first time an enzymatic activity for GDAH/AGMAT. Since agmatine has frequently been proposed as an endogenous neurotransmitter, the current findings clarify important aspects of the metabolism of agmatine and guanidino acid derivatives in humans.

Case Report: Congenital Methaemoglobinaemia Type 1: Benign Cyanosis?

Type 1 congenital methaemoglobinaemia is a rare cause of cyanosis which may manifest in affected individuals during concomitant illness. Treatment indications and aims differ from that of acquired methaemoglobinaemia. Type 1 methaemoglobinaemia is a distinct condition from the type 2 form which has a high mortality rate in infancy. A 25 year old male with known type 1 congential methaemoglobinaemia presented with cyanosis in the context of Influenza A with raised methaemoglobin levels on arterial blood gas analysis. The patient was assessed based on his level of 'functional haemoglobin' with no acute indication for IV methylene blue or ascorbic acid. Consideration could be given to prescription of these on a cosmetic basis for some patient populations.

Discovery of a Ni2+-dependent guanidine hydrolase in bacteria

Nitrogen availability is a growth-limiting factor in many habitats¹, and the global nitrogen cycle involves prokaryotes and eukaryotes competing for this precious resource. Only some bacteria and archaea can fix elementary nitrogen; all other organisms depend on the assimilation of mineral or organic nitrogen. The nitrogen-rich compound guanidine occurs widely in nature^2-4, but its utilization is impeded by pronounced resonance stabilization⁵, and enzymes catalysing hydrolysis of free guanidine have not been identified. Here we describe the arginase family protein GdmH (Sll1077) from Synechocystis sp. PCC 6803 as a Ni²⁺-dependent guanidine hydrolase. GdmH is highly specific for free guanidine. Its activity depends on two accessory proteins that load Ni²⁺ instead of the typical Mn²⁺ ions into the active site. Crystal structures of GdmH show coordination of the dinuclear metal cluster in a geometry typical for arginase family enzymes and allow modelling of the bound substrate. A unique amino-terminal extension and a tryptophan residue narrow the substrate-binding pocket and identify homologous proteins in further cyanobacteria, several other bacterial taxa and heterokont algae as probable guanidine hydrolases. This broad distribution suggests notable ecological relevance of guanidine hydrolysis in aquatic habitats.

Pairwise sequence similarity mapping with PaSiMap: Reclassification of immunoglobulin domains from titin as case study

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A novel multidimensional scaling pipeline for sequence analysis.

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A simple way to distinguish between unique and shared sequence features.

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Titin domains were reclassified, improving upon earlier analysis.

Sequence comparison is critical for the functional assignment of newly identified protein genes. As uncharacterized protein sequences accumulate, there is an increasing need for sensitive tools for their classification. Here, we present a novel multidimensional scaling pipeline, PaSiMap, which creates a map of pairwise sequence similarities. Uniquely, PaSiMap distinguishes between unique and shared features, allowing for a distinct view of protein-sequence relationships. We demonstrate PaSiMap’s efficiency in detecting sequence groups and outliers using titin’s 169 immunoglobulin (Ig) domains. We show that Ig domain similarity is hierarchical, being firstly determined by chain location, then by the loop features of the Ig fold and, finally, by super-repeat position. The existence of a previously unidentified domain repeat in the distal, constitutive I-band is revealed. Prototypic Igs, plus notable outliers, are identified and thereby domain classification improved. This re-classification can now guide future molecular research. In summary, we demonstrate that PaSiMap is a sensitive tool for the classification of protein sequences, which adds a new perspective in the understanding of inter-protein relationships. PaSiMap is applicable to any biological system defined by a linear sequence, including polynucleotide chains.

Titin kinase ubiquitination aligns autophagy receptors with mechanical signals in the sarcomere

Striated muscle undergoes remodelling in response to mechanical and physiological stress, but little is known about the integration of such varied signals in the myofibril. The interaction of the elastic kinase region from sarcomeric titin (A168-M1) with the autophagy receptors Nbr1/p62 and MuRF E3 ubiquitin ligases is well suited to link mechanosensing with the trophic response of the myofibril. To investigate the mechanisms of signal cross-talk at this titin node, we elucidated its 3D structure, analysed its response to stretch using steered molecular dynamics simulations and explored its functional relation to MuRF1 and Nbr1/p62 using cellular assays. We found that MuRF1-mediated ubiquitination of titin kinase promotes its scaffolding of Nbr1/p62 and that the process can be dynamically down-regulated by the mechanical unfolding of a linker sequence joining titin kinase with the MuRF1 receptor site in titin. We propose that titin ubiquitination is sensitive to the mechanical state of the sarcomere, the regulation of sarcomere targeting by Nbr1/p62 being a functional outcome. We conclude that MuRF1/Titin Kinase/Nbr1/p62 constitutes a distinct assembly that predictably promotes sarcomere breakdown in inactive muscle.

Molecular Characterisation of Titin N2A and Its Binding of CARP Reveals a Titin/Actin Cross-linking Mechanism

Striated muscle responds to mechanical overload by rapidly up-regulating the expression of the cardiac ankyrin repeat protein, CARP, which then targets the sarcomere by binding to titin N2A in the I-band region. To date, the role of this interaction in the stress response of muscle remains poorly understood. Here, we characterise the molecular structure of the CARP-receptor site in titin (UN2A) and its binding of CARP. We find that titin UN2A contains a central three-helix bundle fold (ca 45 residues in length) that is joined to N- and C-terminal flanking immunoglobulin domains by long, flexible linkers with partial helical content. CARP binds titin by engaging an α-hairpin in the three-helix fold of UN2A, the C-terminal linker sequence, and the BC loop in Ig81, which jointly form a broad binding interface. Mutagenesis showed that the CARP/N2A association withstands sequence variations in titin N2A and we use this information to evaluate 85 human single nucleotide variants. In addition, actin co-sedimentation, co-transfection in C2C12 cells, proteomics on heart lysates, and the mechanical response of CARP-soaked myofibrils imply that CARP induces the cross-linking of titin and actin myofilaments, thereby increasing myofibril stiffness. We conclude that CARP acts as a regulator of force output in the sarcomere that preserves muscle mechanical performance upon overload stress.

The N2A region of titin has a unique structural configuration

The N2A segment of titin is a main signaling hub in the sarcomeric I-band that recruits various signaling factors and processing enzymes. It has also been proposed to play a role in force production through its Ca²⁺-regulated association with actin. However, the molecular basis by which N2A performs these functions selectively within the repetitive and extensive titin chain remains poorly understood. Here, we analyze the structure of N2A components and their association with F-actin. Specifically, we characterized the structure of its Ig domains by elucidating the atomic structure of the I81-I83 tandem using x-ray crystallography and computing a homology model for I80. Structural data revealed these domains to present heterogeneous and divergent Ig folds, where I81 and I83 have unique loop structures. Notably, the I81-I83 tandem has a distinct rotational chain arrangement that confers it a unique multi-domain topography. However, we could not identify specific Ca²⁺-binding sites in these Ig domains, nor evidence of the association of titin N2A components with F-actin in transfected C2C12 myoblasts or C2C12-derived myotubes. In addition, F-actin cosedimentation assays failed to reveal binding to N2A. We conclude that N2A has a unique architecture that predictably supports its selective recruitment of binding partners in signaling, but that its mechanical role through interaction with F-actin awaits validation.

Exploring Obscurin and SPEG Kinase Biology

Three members of the obscurin protein family that contain tandem kinase domains with important signaling functions for cardiac and striated muscles are the giant protein obscurin, its obscurin-associated kinase splice isoform, and the striated muscle enriched protein kinase (SPEG). While there is increasing evidence for the specific roles that each individual kinase domain plays in cross-striated muscles, their biology and regulation remains enigmatic. Our present study focuses on kinase domain 1 and the adjacent low sequence complexity inter-kinase domain linker in obscurin and SPEG. Using Phos-tag gels, we show that the linker in obscurin contains several phosphorylation sites, while the same region in SPEG remained unphosphorylated. Our homology modeling, mutational analysis and molecular docking demonstrate that kinase 1 in obscurin harbors all key amino acids important for its catalytic function and that actions of this domain result in autophosphorylation of the protein. Our bioinformatics analyses also assign a list of putative substrates for kinase domain 1 in obscurin and SPEG, based on the known and our newly proposed phosphorylation sites in muscle proteins, including obscurin itself.

The importance of chain context in assessing small nucleotide variants in titin: in silico case study of the I10-I11 tandem and its arrhythmic right ventricular cardiomyopathy linked position T2580

Non-synonymous small nucleotide variations (nsSNVs) in the giant muscle protein, titin, have key roles in the development of several myopathologies. Although there is considerable motive to screen at-risk individuals for nsSNVs, to identify patients in early disease stages while therapeutic intervention is still possible, the clinical significance of most titin variations remains unclear. Therefore, there is a growing need to establish methods to classify nsSNVs in a simple, economic and rapid manner. Due to its strong correlation to arrhythmogenic right ventricular cardiomyopathy (ARVC), one particular mutation in titin-T2580I, located in the I10 immunoglobulin domain-has received considerable attention. Here, we use the I10-I11 tandem as a case study to explore the possible benefits of considering the titin chain context-i.e. domain interfaces-in the assessment of titin nsSNVs. Specifically, we investigate which exchanges mimic the conformational molecular phenotype of the T2580I mutation at the I10-I11 domain interface. Then, we computed a residue stability landscape for domains alone and in tandem to define a Domain Interface Score (DIS) which identifies several hotspot residues. Our findings suggest that the T2580 position is highly sensitive to exchange and that any variant found in this position should be considered with care. Furthermore, we conclude that the consideration of the higher order structure of the titin chain is important to gain accurate insights into the vulnerability of positions in linker regions and that titin nsSNV prediction benefits from a contextual analysis. Communicated by Ramaswamy H. Sarma.

The ZT Biopolymer: A Self-Assembling Protein Scaffold for Stem Cell Applications

The development of cell culture systems for the naturalistic propagation, self-renewal and differentiation of cells ex vivo is a high goal of molecular engineering. Despite significant success in recent years, the high cost of up-scaling cultures, the need for xeno-free culture conditions, and the degree of mimicry of the natural extracellular matrix attainable in vitro using designer substrates continue to pose obstacles to the translation of cell-based technologies. In this regard, the ZT biopolymer is a protein-based, stable, scalable, and economical cell substrate of high promise. ZT is based on the naturally occurring assembly of two human proteins: titin-Z1Z2 and telethonin. These protein building blocks are robust scaffolds that can be conveniently functionalized with full-length proteins and bioactive peptidic motifs by genetic manipulation, prior to self-assembly. The polymer is, thereby, fully encodable. Functionalized versions of the ZT polymer have been shown to successfully sustain the long-term culturing of human embryonic stem cells (hESCs), human induced pluripotent stem cells (hiPSCs), and murine mesenchymal stromal cells (mMSCs). Pluripotency of hESCs and hiPSCs was retained for the longest period assayed (4 months). Results point to the large potential of the ZT system for the creation of a modular, pluri-functional biomaterial for cell-based applications.

Self-Assembling Proteins as High-Performance Substrates for Embryonic Stem Cell Self-Renewal

The development of extracellular matrix mimetics that imitate niche stem cell microenvironments and support cell growth for technological applications is intensely pursued. Specifically, mimetics are sought that can enact control over the self-renewal and directed differentiation of human pluripotent stem cells (hPSCs) for clinical use. Despite considerable progress in the field, a major impediment to the clinical translation of hPSCs is the difficulty and high cost of large-scale cell production under xeno-free culture conditions using current matrices. Here, a bioactive, recombinant, protein-based polymer, termed ZT^Fn , is presented that closely mimics human plasma fibronectin and serves as an economical, xeno-free, biodegradable, and functionally adaptable cell substrate. The ZT^Fn substrate supports with high performance the propagation and long-term self-renewal of human embryonic stem cells while preserving their pluripotency. The ZT^Fn polymer can, therefore, be proposed as an efficient and affordable replacement for fibronectin in clinical grade cell culturing. Further, it can be postulated that the ZT polymer has significant engineering potential for further orthogonal functionalization in complex cell applications.

Evolutionary Morphing of Tryptophan Synthase: Functional Mechanisms for the Enzymatic Channeling of Indole

Tryptophan synthase (TrpS) is a heterotetrameric αββα enzyme that exhibits complex substrate channeling and allosteric mechanisms and is a model system in enzymology. In this work, we characterize proposed early and late evolutionary states of TrpS and show that they have distinct quaternary structures caused by insertions-deletions of sequence segments (indels) in the β-subunit. Remarkably, indole hydrophobic channels that connect α and β active sites have re-emerged in both TrpS types, yet they follow different paths through the β-subunit fold. Also, both TrpS geometries activate the α-subunit through the rearrangement of loops flanking the active site. Our results link evolutionary sequence changes in the enzyme subunits with channeling and allostery in the TrpS enzymes. The findings demonstrate that indels allow protein quaternary architectures to escape "minima" in the evolutionary landscape, thereby overcoming the conservational constraints imposed by existing functional interfaces and being free to morph into new mechanistic enzymes.

Autophosphorylation Is a Mechanism of Inhibition in Twitchin Kinase

Titin-like kinases are muscle-specific kinases that regulate mechanical sensing in the sarcomere. Twitchin kinase (TwcK) is the best-characterized member of this family, both structurally and enzymatically. TwcK activity is auto-inhibited by a dual intrasteric mechanism, in which N- and C-terminal tail extensions wrap around the kinase domain, blocking the hinge region, the ATP binding pocket and the peptide substrate binding groove. Physiologically, kinase activation is thought to occur by a stretch-induced displacement of the inhibitory tails from the kinase domain. Here, we now show that TwcK inhibits its catalysis even in the absence of regulatory tails, by undergoing auto-phosphorylation at mechanistically important elements of the kinase fold. Using mass spectrometry, site-directed mutagenesis and catalytic assays on recombinant samples, we identify residues T212, T301, T316 and T401 as primary auto-phosphorylation sites in TwcK in vitro. Taken together, our results suggest that residue T316, located in the peptide substrate binding P+1 loop, is the dominantly regulatory site in TwcK. Based on these findings, we conclude that TwcK is regulated through a triple-inhibitory mechanism consisting of phosphorylation and intrasteric blockage, which is responsive not only to mechanical cues but also to biochemical modulation. This implies that mechanically stretched conformations of TwcK do not necessarily correspond to catalytically active states, as previously postulated. This further suggests a phosphorylation-dependent desensitization of the TwcK-mediated mechanoresponse of the sarcomere in vivo.

Proteomic Identification of Immunodiagnostic Antigens for Trypanosoma vivax Infections in Cattle and Generation of a Proof-of-Concept Lateral Flow Test Diagnostic Device

Trypanosoma vivax is one of the causative agents of Animal African Trypanosomosis in cattle, which is endemic in sub-Saharan Africa and transmitted primarily by the bite of the tsetse fly vector. The parasite can also be mechanically transmitted, and this has allowed its spread to South America. Diagnostics are limited for this parasite and in farm settings diagnosis is mainly symptom-based. We set out to identify, using a proteomic approach, candidate diagnostic antigens to develop into an easy to use pen-side lateral flow test device. Two related members the invariant surface glycoprotein family, TvY486_0045500 and TvY486_0019690, were selected. Segments of these antigens, lacking N-terminal signal peptides and C-terminal transmembrane domains, were expressed in E. coli. Both were developed into ELISA tests and one of them, TvY486_0045500, was developed into a lateral flow test prototype. The tests were all evaluated blind with 113 randomised serum samples, taken from 37 calves before and after infection with T. vivax or T. congolense. The TvY486_0045500 and TvY486_0019690 ELISA tests gave identical sensitivity and specificity values for T. vivax infection of 94.5% (95% CI, 86.5% to 98.5%) and 88.0% (95% CI, 75.7% to 95.5%), respectively, and the TvY486_0045500 lateral flow test prototype a sensitivity and specificity of 92.0% (95% CI, 83.4% to 97.0%) and 89.8% (95% CI, 77.8% to 96.6%), respectively. These data suggest that recombinant TvY486_0045500 shows promise for the development of a pen-side lateral flow test for the diagnosis of T. vivax animal African trypanosomosis.

CARP interacts with titin at a unique helical N2A sequence and at the domain Ig81 to form a structured complex

The cardiac ankyrin repeat protein (CARP) is up-regulated in the myocardium during cardiovascular disease and in response to mechanical or toxic stress. Stress-induced CARP interacts with the N2A spring region of the titin filament to modulate muscle compliance. We characterize the interaction between CARP and titin-N2A and show that the binding site in titin spans the dual domain UN2A-Ig81. We find that the unique sequence UN2A is not structurally disordered, but that it has a stable, elongated α-helical fold that possibly acts as a constant force spring. Our findings portray CARP/titin-N2A as a structured node and help to rationalize the molecular basis of CARP mechanosensing in the sarcomeric I-band.

Exploration of pathomechanisms triggered by a single-nucleotide polymorphism in titin's I-band: the cardiomyopathy-linked mutation T2580I

Missense single-nucleotide polymorphisms (mSNPs) in titin are emerging as a main causative factor of heart failure. However, distinguishing between benign and disease-causing mSNPs is a substantial challenge. Here, we research the question of whether a single mSNP in a generic domain of titin can affect heart function as a whole and, if so, how. For this, we studied the mSNP T2850I, seemingly linked to arrhythmogenic right ventricular cardiomyopathy (ARVC). We used structural biology, computational simulations and transgenic muscle in vivo methods to track the effect of the mutation from the molecular to the organismal level. The data show that the T2850I exchange is compatible with the domain three-dimensional fold, but that it strongly destabilizes it. Further, it induces a change in the conformational dynamics of the titin chain that alters its reactivity, causing the formation of aberrant interactions in the sarcomere. Echocardiography of knock-in mice indicated a mild diastolic dysfunction arising from increased myocardial stiffness. In conclusion, our data provide evidence that single mSNPs in titin's I-band can alter overall muscle behaviour. Our suggested mechanisms of disease are the development of non-native sarcomeric interactions and titin instability leading to a reduced I-band compliance. However, understanding the T2850I-induced ARVC pathology mechanistically remains a complex problem and will require a deeper understanding of the sarcomeric context of the titin region affected.

Proteomic selection of immunodiagnostic antigens for Trypanosoma congolense

Animal African Trypanosomosis (AAT) presents a severe problem for agricultural development in sub-Saharan Africa. It is caused by several trypanosome species and current means of diagnosis are expensive and impractical for field use. Our aim was to discover antigens for the detection of antibodies to Trypanosoma congolense, one of the main causative agents of AAT. We took a proteomic approach to identify potential immunodiagnostic parasite protein antigens. One hundred and thirteen proteins were identified which were selectively recognized by infected cattle sera. These were assessed for likelihood of recombinant protein expression in E. coli and fifteen were successfully expressed and assessed for their immunodiagnostic potential by ELISA using pooled pre- and post-infection cattle sera. Three proteins, members of the invariant surface glycoprotein (ISG) family, performed favorably and were then assessed using individual cattle sera. One antigen, Tc38630, evaluated blind with 77 randomized cattle sera in an ELISA assay gave sensitivity and specificity performances of 87.2% and 97.4%, respectively. Cattle immunoreactivity to this antigen diminished significantly following drug-cure, a feature helpful for monitoring the efficacy of drug treatment.

Animal African Trypanosomosis (AAT) is a set of diseases whereby animals are infected with single-cell parasites that replicate in their bloodstream. The disease in cattle results in weight-loss and death, and AAT is a significant veterinary problem for sub-Saharan Africa. One of the principal trypanosome species responsible for AAT in cattle is Trypanosoma congolense and, although there are drug-treatments for these infections, current diagnostic methods are impractical for field use. Our aim was to discover protein molecules from the parasite to which infected animals make antibodies, to then make these proteins in bacteria and to subsequently demonstrate that they can be used to detect antibodies in cattle serum, thus diagnosing AAT. To discover the diagnostic proteins, we dissolved parasites in a detergent solution and applied them to beads coated with antibodies from infected cattle and to beads coated with antibodies from un-infected cattle. We then compared the proteins bound to each and selected those proteins that were at least 100-fold enriched by the infected cattle antibodies. We refined this list, according to practical and performance considerations, and settled on one protein, called Tc38630. Testing Tc38630 with cattle sera showed that it can detect about nine out of ten AAT infections.

The architecture of Trypanosoma brucei tubulin-binding cofactor B and implications for function

Tubulin-binding cofactor (TBC)-B is implicated in the presentation of α-tubulin ready to polymerize, and at the correct levels to form microtubules. Bioinformatics analyses, including secondary structure prediction, CD, and crystallography, were combined to characterize the molecular architecture of Trypanosoma brucei TBC-B. An efficient recombinant expression system was prepared, material-purified, and characterized by CD. Extensive crystallization screening, allied with the use of limited proteolysis, led to structures of the N-terminal ubiquitin-like and C-terminal cytoskeleton-associated protein with glycine-rich segment domains at 2.35-Å and 1.6-Å resolution, respectively. These are compact globular domains that appear to be linked by a flexible segment. The ubiquitin-like domain contains two lysines that are spatially conserved with residues known to participate in ubiquitinylation, and so may represent a module that, through covalent attachment, regulates the signalling and/or protein degradation associated with the control of microtubule assembly, catastrophe, or function. The TBC-B C-terminal cytoskeleton-associated protein with glycine-rich segment domain, a known tubulin-binding structure, is the only such domain encoded by the T. brucei genome. Interestingly, in the crystal structure, the peptide-binding groove of this domain forms intermolecular contacts with the C-terminus of a symmetry-related molecule, an association that may mimic interactions with the C-terminus of α-tubulin or other physiologically relevant partners. The interaction of TBC-B with the α-tubulin C-terminus may, in particular, protect from post-translational modifications, or simply assist in the shepherding of the protein into polymerization.

Crystal structure of Leishmania major ADP-ribosylation factor-like 1 and a classification of related GTPase family members in this Kinetoplastid

ADP-ribosylation factor-like (ARL) proteins are small GTPases that undergo conformational changes upon nucleotide binding, and which regulate the affinity of ARLs for binding other proteins, lipids or membranes. There is a paucity of structural data on this family of proteins in the Kinetoplastida, despite studies implicating them in key events related to vesicular transport and regulation of microtubule-dependent processes. The crystal structure of Leishmania major ARL1 in complex with GDP has been determined to 2.1 Å resolution and reveals a high degree of structural conservation with human ADP-ribosylation factor 1 (ARF1). Putative L. major and Trypanosoma brucei ARF/ARL family members have been classified based on structural considerations, amino acid sequence conservation combined with functional data on Kinetoplastid and human orthologues. This classification may guide future studies designed to elucidate the function of specific family members.

Lipolysis and Proteolysis of Modified and Producer Milks Used for Calibration of Mid-Infrared Milk Analyzers

Our objective was to determine if lipolysis or proteolysis of calibration sets during shelf life influenced the mid-infrared (MIR) readings or calibration slopes and intercepts. The lipolytic and proteolytic deterioration was measured for 3 modified milk and 3 producer milk calibration sets during storage at 4 degrees C. Modified and producer milk sets were used separately to calibrate an optical filter and virtual filter MIR analyzer. The uncorrected readings and slopes and intercepts of the calibration linear regressions for fat B, fat A, protein, and lactose were determined over 28 d for modified milks and 15 d for producer milks. It was expected that increases in free fatty acid content and decreases in the casein as a percentage of true protein of the calibration milks would have an effect on the MIR uncorrected readings, calibration slopes and intercepts, and MIR predicted readings. However, the influence of lipolysis and proteolysis on uncorrected readings was either not significant, or significant but very small. Likewise, the amount of variation accounted for by day of storage at 4 degrees C of a calibration set on the calibration slopes and intercepts was also very small. Most of the variation in uncorrected readings and calibration slopes and intercepts were due to differences between the optical filter and virtual filter analyzers and differences between the pasteurized modified milk and raw producer milk calibration sets, not due to lipolysis or proteolysis. The combined impact of lipolysis and proteolysis on MIR predicted values was <0.01% in most cases.

Modified Versus Producer Milk Calibration: Mid-Infrared Analyzer Performance Validation

Our objective was to determine the validation performance of mid-infrared (MIR) milk analyzers, using the traditional fixed-filter approach, when the instruments were calibrated with producer milk calibration samples vs. modified milk calibration samples. Ten MIR analyzers were calibrated using producer milk calibration sample sets, and 9 MIR milk analyzers were calibrated using modified milk sample sets. Three sets of 12 validation milk samples with all-laboratory mean chemistry reference values were tested during a 3-mo period. Calibration of MIR milk analyzers using modified milk increased the accuracy (i.e., better agreement with chemistry) and improved agreement between laboratories on validation milk samples compared with MIR analyzers calibrated with producer milk samples. Calibration of MIR analyzers using modified milk samples reduced overall mean Euclidian distance for all components for all 3 validation sets by at least 24% compared with MIR analyzers calibrated with producer milk sets. Calibration with modified milk sets reduced the average Euclidian distance from all-laboratory mean reference chemistry on validation samples by 40, 25, 36, and 27%, respectively for fat, anhydrous lactose, true protein, and total solids. Between-laboratory agreement was evaluated using reproducibility standard deviation (s(R)). The number of single Grubbs statistical outliers in the validation data was much higher (53 vs. 7) for the instruments calibrated with producer milk than for instruments calibrated with modified milk sets. The s(R) for instruments calibrated with producer milks (with statistical outliers removed) was similar to data collected in recent proficiency studies, whereas the s(R) for instruments calibrated with modified milks was lower than those calibrated with producer milks by 46, 52, 61, and 55%, respectively for fat, anhydrous lactose, true protein, and total solids.

Calibration of Infrared Milk Analyzers: Modified Milk Versus Producer Milk

Mid-infrared (MIR) milk analyzers are traditionally calibrated using sets of preserved raw individual producer milk samples. The goal of this study was to determine if the use of sets of preserved pasteurized modified milks improved calibration performance of MIR milk analyzers compared with calibration sets of producer milks. The preserved pasteurized modified milk sets exhibited more consistent day-to-day and set-to-set calibration slope and intercept values for all components compared with the preserved raw producer milk calibration sets. Pasteurized modified milk calibration samples achieved smaller confidence interval (CI) around the regression line (i.e., calibration uncertainty). Use of modified milk calibration sets with a larger component range, more even distribution of component concentrations within the ranges, and the lower correlation of fat and protein concentrations than producer milk calibration sets produced a smaller 95% CI for the regression line due to the elimination of moderate and high leverage samples. The CI for the producer calibration sets were about 2 to 12 times greater than the CI for the modified milk calibration sets, depending on the component. Modified milk calibration samples have the potential to produce MIR milk analyzer calibrations that will perform better in validation checks than producer milk-based calibrations by reducing the mean difference and standard deviation of the difference between instrument values and reference chemistry.

Precalibration Evaluation Procedures for Mid-Infrared Milk Analyzers

The purpose of this paper is to present a detailed account of the precalibration procedures developed and implemented by the USDA Federal Milk Market Administrators (FMMA) for evaluating mid-infrared (MIR) milk analyzers. Mid-infrared analyzers specifically designed for milk testing provide a rapid and cost-effective means for determining milk composition for payment and dairy herd improvement programs. These instruments determine the fat, protein, and lactose content of milk, and enable the calculation of total solids, solids-not-fat, and other solids. All MIR analyzers are secondary testing instruments that require calibration by chemical reference methods. Precalibration is the process of assuring that the instrument is in good working order (mechanically and electrically) and that the readings before calibration are stable and optimized. The main components of precalibration are evaluation of flow system integrity, homogenization efficiency, water repeatability, zero shift, linearity, primary slope, milk repeatability, purging efficiency, and establishment of intercorrection factors. These are described in detail and apply to both filter-based and Fourier transform infrared instruments operating using classical primary and reference wavelengths. Under the USDA FMMA Precalibration Evaluation Program, the precalibration procedures were applied longitudinally over time using a wide variety of instruments and instrument models. Instruments in this program were maintained to pass the criteria for all precalibration procedures. All instruments used similar primary wavelengths to measure fat, protein, and lactose but there were differences in reference wavelength selection. Intercorrection factors were consistent over time within all instruments and similar among groups of instruments using similar primary and reference wavelengths. However, the magnitude and sign of the intercorrection factors were significantly affected by the choice of reference wavelengths.

Indirect and direct determination of the casein content of milk by Kjeldahl nitrogen analysis: collaborative study

The classic method for determination of milk casein is based on precipitation of casein at pH 4.6. Precipitated milk casein is removed by filtration and the nitrogen content of either the precipitate (direct casein method) or filtrate (noncasein nitrogen; NCN) is determined by Kjeldahl analysis. For the indirect casein method, milk total nitrogen (TN; Method 991.20) is also determined and casein is calculated as TN minus NCN. Ten laboratories tested 9 pairs of blind duplicate raw milk materials with a casein range of 2.42-3.05% by both the direct and indirect casein methods. Statistical performance expressed in protein equivalents (nitrogen x 6.38) with invalid and outlier data removed was as follows: NCN method (wt%), mean = 0.762, sr = 0.010, sR = 0.016, repeatability relative standard deviation (RSDr) = 1.287%, reproducibility relative standard deviation (RSDr) = 2.146%; indirect casein method (wt%), mean = 2.585, repeatability = 0.015, reproducibility = 0.022, RSDr = 0.560%, RSDR = 0.841; direct casein method (wt%), mean = 2.575, sr = 0.015, sR = 0.025, RSDr = 0.597%, RSDR = 0.988%. Method performance was acceptable and comparable to similar Kjeldahl methods for determining nitrogen content of milk (Methods 991.20, 991.21, 991.22, 991.23). The direct casein, indirect casein, and noncasein nitrogen methods have been adopted by AOAC INTERNATIONAL.

Performance evaluation of direct forced-air total solids and Kjeldahl total nitrogen methods: 1990 through 1995

Results from collaborative studies of the performance of the direct forced-air oven-drying method for determination of milk total solids content (AOAC Method 990.20) and the Kjeldahl total nitrogen method for determination of milk total nitrogen content (AOAC Method 991.20) were published in 1989 and 1990, respectively. Method performance was characterized by using the harmonized ISO/IU-PAC/AOAC guidelines for method validation, and the methods now have final action status. During 1990 through 1995, the split sample collaborative study format was used to monitor the performance of these methods as part of a multilaboratory quality assurance program. Seven blind duplicate milk materials were sent from a central laboratory once every 2 months to participating laboratories. Data were analyzed with the same statistical procedures used in the original collaborative studies. Compared with the original collaborative study, the repeatability and reproducibility of the oven-drying method improved over time. For the Kjeldahl total nitrogen method, within-laboratory repeatability improved slightly, whereas between-laboratory reproducibility was similar to but not always as good as in the original study. The results demonstrate that the statistical protocol for collaborative studies can be used effectively as the basis for a multilaboratory quality assurance program and that the method performance achieved in a collaborative study can be maintained and even improved with time.

Multilevel anterior cervical corpectomy and fibular allograft fusion for cervical myelopathy

This study was conducted to determine the safety and efficacy of multilevel anterior cervical corpectomy and stabilization using fibular allograft in patients with cervical myelopathy. Thirty-six patients underwent this procedure for cervical myelopathy caused by spondylosis (20 patients), ossified posterior longitudinal ligament (four patients), trauma (one patient), or a combination of lesions (11 patients). The mean age (+/- standard deviation) of the patients was 58 +/- 10 years and 30 of the patients were men. The mean duration of symptoms before surgery was 30 +/- 6 months and 11 patients had undergone previous surgery. Prior to surgery, the mean Nurick grade of the myelopathy was 3.1 +/- 1.4. Seventeen patients also had cervicobrachial pain. Four vertebrae were removed in six patients, three in 19, and two in 11 patients. Instrumentation was used in 15 cases. The operative mortality rate was 3% (one patient) and two patients died 2 months postoperatively. Postoperative complications included early graft displacement requiring reoperation (three patients), transient dysphagia (two patients), cerebrospinal fluid leak treated by lumbar drainage (three patients), myocardial infarction (two patients), and late graft fracture (one patient). One patient developed transient worsening of myelopathy and three developed new, temporary radiculopathies. All patients achieved stable bone union and the mean Nurick grade at an average of 31 +/- 20 months (range 0-79 months) postoperatively was 2.4 +/- 1.6 (p < 0.05, t-test). Cervicobrachial pain improved in 10 (59%) of the 17 patients who had preoperative pain and myelopathy improved at least one grade in 17 patients (47%; p < 0.05). Twenty-six surviving patients (72%) were followed for more than 24 months and stable, osseous union occurred in 97%. These results show that extensive, multilevel anterior decompression and stabilization using fibular allograft can be achieved with a perioperative mortality and major morbidity rate of 22% and with significant improvement in pain and myelopathy.

Comparison of Babcock and ether extraction methods for determination of fat content of cream: collaborative study

A modified Mojonnier ether extraction method for determination of the fat content of cream was developed based on the method for milk (AOAC Official Method 989.05). The cream Babcock method (AOAC Official Method 920.111B-C) was modified to harmonize with the milk Babcock method (AOAC Official Method 989.04) and to clarify procedural details. Using the AOAC collaborative study format, 10 laboratories tested 9 pairs of blind duplicate heat-treated cream samples with a fat range of 30-45% using both methods. The statistical performance (invalid and outlier data removed) was as follows: mean % fat = 37.932, Sr = 0.125, SR = 0.151, RSDr = 0.330, RSDR = 0.398, r = 0.354, and R = 0.427 for the ether extraction method. For the Babcock method, mean % fat = 38.209, Sr = 0.209, SR = 0.272, RSDr = 0.548, RSDR = 0.712, r = 0.592, and R = 0.769. Average test results for fat from the Babcock method were 0.277% (absolute fat) greater than for the Mojonnier ether extraction method. The difference between methods, as a percentage of the average fat content of the samples, was 0.73%. This agrees with differences observed between the 2 methods for milk when 10 to 17 laboratories tested 7 milk samples in blind duplicate at bimonthly intervals over a 4-year period (average difference 0.029% fat, 0.78% as a percentage of average fat content). The Mojonnier ether extraction and Babcock methods for fat in cream have been adopted by AOAC INTERNATIONAL. The new Babcock method replaced the AOAC Official Method 920.111B-C.

What in the world is being done about TBAs? An overview of international and national attitudes to traditional birth attendants

Many of the half million women per year who die in childbirth are attended by traditional birth attendants (TBAs). Whether they fare better when such an attendant is trained remains uncertain; even the World Health Organization seems to have tempered its enthusiasm for TBA training recently. With some nations outlawing the practice of TBAs and others actively promoting it, there seems to be no consensus on what to do about this major and continuing workforce in maternity care. By themselves TBAs cannot reduce maternal mortality, whether they are trained or not. They need skilled, equipped and available support. As the professional group who must co-operate with TBAs and provide that support, midwives must, collectively and individually, assess, state and act on their attitude towards TBAs.

Effect of infrared analyzer homogenization efficiency on repeatability of uncorrected fat A and fat B signals

Poor repeatability by infrared milk analyzers may be caused by inefficient homogenization as a result of light scattering and the Christiansen effect. The objectives of this study were to identify instruments with good and poor homogenization efficiency and to determine if a difference exists in repeatability performance between instruments with good vs poor homogenization efficiency. Unhomogenized and homogenized portions of the same milk were tested 20 times consecutively on 22 instruments. An instrument was considered to have poor homogenization efficiency if the mean difference in the uncorrected signal between unhomogenized and homogenized portions of the same milk was > or = 1.43% of the fat test (i.e., > or = 0.05% at 3.5% fat). Instruments were evaluated for repeatability by calculating the sample standard deviation and the range of the latter 19 uncorrected readings for unhomogenized and homogenized milks. When repeatability was evaluated as a function of homogenization efficiency, there was a significant (p = 0.001) correlation between poor homogenization efficiency and poor repeatability when testing unhomogenized milk but not when testing homogenized milk. Improved homogenizer performance within infrared milk analyzers is needed to improve the repeatability of raw milk testing.

Effect of infrared analyzer homogenization efficiency on linearity of uncorrected fat A and fat B signals

The objective of the survey was to determine if poor homogenizer performance causes nonlinear behavior of the uncorrected fat A or fat B signal that is not detected when an instrument's residual nonlinearity is determined by using dilutions of homogenized milk instead of unhomogenized milk. Unhomogenized and homogenized (17238 kPa) portions of the same 6.1% fat milk were tested on 20 instruments to determine homogenization efficiency. Instruments with differences of > or = 0.087% fat between homogenized and unhomogenized portions of the same milk had inefficient homogenization, on the basis of criteria established in a previous study. Four and 12 instruments out of 20 demonstrated inefficient homogenization for the fat A and fat B channels, respectively. Uncorrected signal linearity for the fat channels was evaluated quantitatively by using a series of dilutions of homogenized (17238 kPa) and unhomogenized milks. Most instruments passed the linearity evaluation for dilutions of either homogenized or unhomogenized milk, even though many of the same instruments failed the homogenization efficiency evaluation. Thus, using dilutions of homogenized milk is valid for linearity evaluation of instruments being used for testing unhomogenized milk in the range of fat concentrations used for payment testing.

Induction of lactation: histological and biochemical development of mammary tissue and milk yields of cows injected with estradiol-17 beta and progesterone for 21 days

Lactations were induced in nonpregnant, nonlactating dairy cows by subcutaneous injections of estradiol-17 beta and progesterone for 21 d (.10 and .25 mg/kg body weight/d) and dexamethasone (.028 mg/kg body weight/d) on d 31 to 34. Milking was initiated on d 35. Each cow was biopsied two or three times during the experiment with five to eight mammary tissue biopsies on d 0, 7, 14, 21, 28, 35, 49, and 130. Mammary tissue preinjection had abundant connective and adipose tissues with limited lobuloalveolar structures. Beginning on d 7, there was decreased stroma, increased epithelial cell area, increased lobuloalveolar architecture, plus the accumulation of intracellular and intraluminal secretions which were high in lipid droplets. From d 7 through 35, these changes were progressive although variable among cows. Changes in activities of enzymes and concentrations of ribonucleic acid and deoxyribonucleic acid were gradual during this time but essentially paralleled histological development. Tissue samples during lactation (d 49 and 130) showed increased histological and biochemical development; development was maximal for d 130 samples. Fourteen of 15 cows that lactated had mean daily yields of milk more than 5 kg and yields of milk of 12 cows with projected or actual 305-d lactations were 63.0% of that during their previous natural lactations. Reasons for less yields of milk and for varied patterns of tissue development were not identified nor explained by concentrations of several selected hormones in plasma.

Wheat Gibberellins

Two "gibberellin-like" substances were present in malted wheat, compared to only one in sound, unmalted wheat. Alcoholic extracts of wheat malt fractionated by paper chromatography and bioassayed for gibberellin-like activity by three methods, indicated a new gibberellin in malted wheat. This component increased particularly in the embryo section of the sprouted wheat during the first 3 to 4 days of germination.