An allosteric switch ensures efficient unidirectional information transmission by the histidine kinase DesK from Bacillus subtilis

Allosteric coupling activation mechanism in histidine kinases

Histidine kinases (HKs) are crucial regulators of cellular functions, mediating the phosphorylation of specific proteins to modulate their activity and localization. Upon signal detection, HKs transfer a phosphate group from ATP to a conserved histidine residue within their Dimerization and Histidine phosphotransfer domain, subsequently passing the phosphate to a response regulator (RR) that typically interacts with DNA promoters to regulate gene expression. This study investigates the signal transduction mechanism of Bacillus subtilis HK DesK. We generated substitutions on the conserved phospho-acceptor histidine and evaluated their effects on DesK's activity in both in vivo and in vitro contexts. Notably, we found that a variant of DesK lacking the conserved histidine could still activate gene expression. Furthermore, computational simulations of DesK variants complexed with DesR revealed interactions that could be required to maintain DesR's active conformation. Our findings elucidate an alternative pathway for RR activation via an allosteric mechanism that operates independently of histidine phosphorylation. We also demonstrated that Escherichia coli HK EnvZ, when lacking the conserved histidine, can activate gene expression. This HK-Allosteric Coupling Activation Mechanism functions without reliance on phosphorylation or ATP consumption, potentially serving as a fail-safe mechanism under nutrient-limited conditions.

Evolved enzymes in the metabolism of biological poly-acids: Applications in otolaryngological biocatalysis

This study explores evolved Hyaluronidase, Lipase, and Elastase's identification, characterization, and therapeutic potential to enhance tissue regeneration and drug delivery systems in otolaryngology. Hyaluronidase variant H5 exhibited a turnover number (k_cat) of 1500 min-1, a 200 % increase over wild-type (500 min-1), demonstrating superior hyaluronic acid degradation. Similarly, lipase variant L2 reached 1200 min-1 (400 min-1 wild-type), and elastase variant E3 showed a turnover of 2200 min-1 (1000 min-1 wild-type). Kinetic analyses revealed improved Km and Vmax values across variants, with Hyaluronidase Variant H5 achieving Km = 1.5 μM and Vmax = 3000 μM/min. Molecular Dynamics (MD) simulations indicated structural stability (average RMSD ~1.5 Å for H5) and strong hydrogen bonding (180 bonds), enhancing catalytic efficiency. In vitro assays demonstrated a 40 % enhancement in tissue regeneration and increased epithelial cell proliferation (100 % for Hyaluronidase Variant H5 vs. 60 % wild-type). In vivo studies in rabbits revealed a 30 % reduction in recovery time post-sinus surgery and a 50 % reduction in scar tissue formation. These findings underscore the potential of evolved enzymes in advancing drug delivery (DD) and tissue repair (TR), with implications for broader applications in wound healing and inflammatory diseases.

Allostery in Disease: Anticancer Drugs, Pockets, and the Tumor Heterogeneity Challenge

Charting future innovations is challenging. Yet, allosteric and orthosteric anticancer drugs are undergoing a revolution and taxing unresolved dilemmas await. Among the imaginative innovations, here we discuss cereblon and thalidomide derivatives as a means of recruiting neosubstrates and their degradation, allosteric heterogeneous bifunctional drugs like PROTACs, drugging phosphatases, inducers of targeted posttranslational protein modifications, antibody-drug conjugates, exploiting membrane interactions to increase local concentration, stabilizing the folded state, and more. These couple with harnessing allosteric cryptic pockets whose discovery offers more options to modulate the affinity of orthosteric, active site inhibitors. Added to these are strategies to counter drug resistance through drug combinations co-targeting pathways to bypass signaling blockades. Here, we discuss on the molecular and cellular levels, such inspiring advances, provide examples of their applications, their mechanisms and rational. We start with an overview on difficult to target proteins and their properties-rarely, if ever-conceptualized before, discuss emerging innovative drugs, and proceed to the increasingly popular allosteric cryptic pockets-their advantages-and critically, issues to be aware of. We follow with drug resistance and in-depth discussion of tumor heterogeneity. Heterogeneity is a hallmark of highly aggressive cancers, the core of drug resistance unresolved challenge. We discuss potential ways to target heterogeneity by predicting it. The increase in experimental and clinical data, computed (cell-type specific) interactomes, capturing transient cryptic pockets, learned drug resistance, workings of regulatory mechanisms, heterogeneity, and resistance-based cell signaling drug combinations, assisted by AI-driven reasoning and recognition, couple with creative allosteric drug discovery, charting future innovations.

Signal-sensing triggers the shutdown of HemKR, regulating heme and iron metabolism in the spirochete Leptospira biflexa

Heme and iron metabolic pathways are highly intertwined, both compounds being essential for key biological processes, yet becoming toxic if overabundant. Their concentrations are exquisitely regulated, including via dedicated two-component systems (TCSs) that sense signals and regulate adaptive responses. HemKR is a TCS present in both saprophytic and pathogenic Leptospira species, involved in the control of heme metabolism. However, the molecular means by which HemKR is switched on/off in a signal-dependent way, are still unknown. Moreover, a comprehensive list of HemKR-regulated genes, potentially overlapped with iron-responsive targets, is also missing. Using the saprophytic species Leptospira biflexa as a model, we now show that 5-aminolevulinic acid (ALA) triggers the shutdown of the HemKR pathway in live cells, and does so by stimulating the phosphatase activity of HemK towards phosphorylated HemR. Phospho~HemR dephosphorylation leads to differential expression of multiple genes, including of heme metabolism and transport systems. Besides the heme-biosynthetic genes hemA and the catabolic hmuO, which we had previously reported as phospho~HemR targets, we now extend the regulon identifying additional genes. Finally, we discover that HemR inactivation brings about an iron-deficit tolerant phenotype, synergistically with iron-responsive signaling systems. Future studies with pathogenic Leptospira will be able to confirm whether such tolerance to iron deprivation is conserved among Leptospira spp., in which case HemKR could play a vital role during infection where available iron is scarce. In sum, HemKR responds to abundance of porphyrin metabolites by shutting down and controlling heme homeostasis, while also contributing to integrate the regulation of heme and iron metabolism in the L. biflexa spirochete model.

Mechanism of activation and autophosphorylation of a histidine kinase

Histidine kinases (HK) are one of the main prokaryotic signaling systems. Two structurally conserved catalytic domains inside the HK enable autokinase, phosphotransfer, and phosphatase activities. Here, we focus on a detailed mechanistic understanding of the functional cycle of the WalK HK by a multi-scale simulation approach, consisting of classical as well as hybrid QM/MM molecular dynamics simulation. Strikingly, a conformational transition induced solely in DHp leads to the correct activated conformation in CA crucial for autophosphorylation. This finding explains how variable sensor domains induce the transition from inactive to active state. The subsequent autophosphorylation inside DHp proceeds via a penta-coordinated transition state to a protonated phosphohistidine intermediate. This intermediate is consequently deprotonated by a suitable nearby base. The reaction energetics are controlled by the final proton acceptor and presence of a magnesium cation. The slow rates of the process result from the high energy barrier of the conformational transition between inactive and active states. The phosphorylation step exhibits a lower barrier and down-the-hill energetics. Thus, our work suggests a detailed mechanistic model for HK autophosphorylation.

Structural and functional insights underlying recognition of histidine phosphotransfer protein in fungal phosphorelay systems

In human pathogenic fungi, receiver domains from hybrid histidine kinases (hHK) have to recognize one HPt. To understand the recognition mechanism, we have assessed phosphorelay from receiver domains of five hHKs of group III, IV, V, VI, and XI to HPt from Chaetomium thermophilum and obtained the structures of Ct_HPt alone and in complex with the receiver domain of hHK group VI. Our data indicate that receiver domains phosphotransfer to Ct_HPt, show a low affinity for complex formation, and prevent a Leu-Thr switch to stabilize phosphoryl groups, also derived from the structures of the receiver domains of hHK group III and Candida albicans Sln1. Moreover, we have elucidated the envelope structure of C. albicans Ypd1 using small-angle X-ray scattering which reveals an extended flexible conformation of the long loop αD-αE which is not involved in phosphotransfer. Finally, we have analyzed the role of salt bridges in the structure of Ct_HPt alone.

Investigation into the potential mechanism of Bacillus amyloliquefaciens in the fermentation of broad bean paste by metabolomics and transcriptomics

Pixian broad bean paste is a renowned fermented seasoning. The fermentation of broad bean is the most important process of Pixian broad bean paste. To enhance the flavor of tank-fermented broad bean paste, salt-tolerant Bacillus amyloliquefaciens strain was inoculated, resulting in an increase in total amount of volatile compounds, potentially leading to different flavor characteristics. To investigate the fermentation mechanism, monoculture simulated fermentation systems were designed. Metabolomics and transcriptomics were used to explore Bacillus amyloliquefaciens' transcriptional response to salt stress and potential aroma production mechanisms. The results highlighted different metabolite profiles under salt stress, and the crucial roles of energy metabolism, amino acid metabolism, reaction system, transportation system in Bacillus amyloliquefaciens' hypersaline stress response. This study provides a scientific basis for the industrial application of Bacillus amyloliquefaciens and new insights into addressing the challenges of poor flavor quality in tank fermentation products.

Structural features of sensory two component systems: a synthetic biology perspective

All living organisms include a set of signaling devices that confer the ability to dynamically perceive and adapt to the fluctuating environment. Two-component systems are part of this sensory machinery that regulates the execution of different genetic and/or biochemical programs in response to specific physical or chemical signals. In the last two decades, there has been tremendous progress in our molecular understanding on how signals are detected, the allosteric mechanisms that control intramolecular information transmission and the specificity determinants that guarantee correct wiring. All this information is starting to be exploited in the development of new synthetic networks. Connecting multiple molecular players, analogous to programming lines of code, can provide the resources to build new sophisticated biocomputing systems. The Synthetic Biology field is starting to revolutionize several scientific fields, such as biomedicine and agriculture, propelling the development of new solutions. Expanding the spectrum of available nanodevices in the toolbox is key to unleash its full potential. This review aims to discuss, from a structural perspective, how to take advantage of the vast array of sensor and effector protein modules involved in two-component systems for the construction of new synthetic circuits.