Identification of Potential Binders of Mtb Universal Stress Protein (Rv1636) Through an in silico Approach and Insights Into Compound Selection for Experimental Validation

Cyclic AMP binding to a universal stress protein in Mycobacterium tuberculosis is essential for viability

Mycobacterial genomes encode multiple adenylyl cyclases and cAMP effector proteins, underscoring the diverse ways these bacteria utilize cAMP. We identified universal stress proteins (USP), Rv1636, and MSMEG_3811 in M. tuberculosis and M. smegmatis, respectively, as abundantly expressed, novel cAMP-binding proteins. Rv1636 is secreted via the SecA2 secretion system in M. tuberculosis but is not directly responsible for the efflux of cAMP from the cell. In slow-growing mycobacteria, intrabacterial concentrations of Rv1636 were equivalent to the concentrations of cAMP present in the cell. In contrast, levels of intrabacterial MSMEG_3811 in M. smegmatis were lower than that of cAMP and therefore, overexpression of Rv1636 increased levels of 'bound' cAMP. While msmeg_3811 could be readily deleted from the genome of M. smegmatis, we find that the rv1636 gene is essential for the viability of M. tuberculosis and is dependent on the cAMP-binding ability of Rv1636. Therefore, Rv1636 may function to regulate cAMP signaling by direct sequestration of the second messenger. This is the first evidence of a 'sponge' for any second messenger in bacterial signaling that would allow mycobacterial cells to regulate the available intrabacterial 'free' pool of cAMP.

Structures, functions, and regulatory networks of universal stress proteins in clinically relevant pathogenic Bacteria

Universal stress proteins are a class of proteins widely present in bacteria, archaea, plants, and invertebrates, playing essential roles in bacterial adaptation to various environmental stresses. The functions of bacterial universal stress proteins are versatile, including resistance to oxidative stress, maintenance of cell wall integrity, DNA damage repair, regulation of cell division and growth, among others. When facing stresses such as temperature changes, pH shifts, fluctuations in oxygen concentration, and exposure to toxins, these proteins can bind to specific DNA sequences and rapidly adjust bacterial metabolic pathways and gene expression patterns to adapt to the new environment. In summary, bacterial universal stress proteins play a crucial role in bacterial adaptability and survival. A comprehensive understanding of bacterial stress response mechanisms and the development of new antibacterial strategies are of great significance. This review summarizes the research progress on the structure, function, and regulatory factors of universal stress proteins in clinically relevant bacteria, aiming to facilitate deeper investigations by clinicians and researchers into universal stress proteins.

The efflux pumps Rv1877 and Rv0191 play differential roles in the protection of Mycobacterium tuberculosis against chemical stress

Background

It was previously shown that GlnA3sc enabled Streptomyces coelicolor to survive in excess polyamines. However, subsequent studies revealed that Rv1878, the corresponding Mycobacterium tuberculosis (M.tb) ortholog, was not essential for the detoxification of spermine (Spm), in M.tb. On the other hand, the multi-drug efflux pump Rv1877 was previously shown to enable export of a wide range of compounds, while Rv0191 was shown to be more specific to chloramphenicol.

Rationale

Therefore, we first wanted to determine if detoxification of Spm by efflux can be achieved by any efflux pump, or if that was dependent upon the function of the pump. Next, since Rv1878 was found not to be essential for the detoxification of Spm, we sought to follow-up on the investigation of the physiological role of Rv1878 along with Rv1877 and Rv0191.

Approach

To evaluate the specificity of efflux pumps in the mycobacterial tolerance to Spm, we generated unmarked ∆rv1877 and ∆rv0191 M.tb mutants and evaluated their susceptibility to Spm. To follow up on the investigation of any other physiological roles they may have, we characterized them along with the ∆rv1878 M.tb mutant.

Results

The ∆rv1877 mutant was sensitive to Spm stress, while the ∆rv0191 mutant was not. On the other hand, the ∆rv1878 mutant grew better than the wild-type during iron starvation yet was sensitive to cell wall stress. The proteins Rv1877 and Rv1878 seemed to play physiological roles during hypoxia and acidic stress. Lastly, the ∆rv0191 mutant was the only mutant that was sensitive to oxidative stress.

Conclusion

The multidrug MFS-type efflux pump Rv1877 is required for Spm detoxification, as opposed to Rv0191 which seems to play a more specific role. Moreover, Rv1878 seems to play a role in the regulation of iron homeostasis and the reconstitution of the cell wall of M.tb. On the other hand, the sensitivity of the ∆rv0191 mutant to oxidative stress, suggests that Rv0191 may be responsible for the transport of low molecular weight thiols.

Binding and Dynamics Demonstrate the Destabilization of Ligand Binding for the S688Y Mutation in the NMDA Receptor GluN1 Subunit

Encephalopathies are brain dysfunctions that lead to cognitive, sensory, and motor development impairments. Recently, the identification of several mutations within the N-methyl-D-aspartate receptor (NMDAR) have been identified as significant in the etiology of this group of conditions. However, a complete understanding of the underlying molecular mechanism and changes to the receptor due to these mutations has been elusive. We studied the molecular mechanisms by which one of the first mutations within the NMDAR GluN1 ligand binding domain, Ser688Tyr, causes encephalopathies. We performed molecular docking, randomly seeded molecular dynamics simulations, and binding free energy calculations to determine the behavior of the two major co-agonists: glycine and D-serine, in both the wild-type and S688Y receptors. We observed that the Ser688Tyr mutation leads to the instability of both ligands within the ligand binding site due to structural changes associated with the mutation. The binding free energy for both ligands was significantly more unfavorable in the mutated receptor. These results explain previously observed in vitro electrophysiological data and provide detailed aspects of ligand association and its effects on receptor activity. Our study provides valuable insight into the consequences of mutations within the NMDAR GluN1 ligand binding domain.

Advances in computational frameworks in the fight against TB: The way forward

Around 1.6 million people lost their life to Tuberculosis in 2021 according to WHO estimates. Although an intensive treatment plan exists against the causal agent, Mycobacterium Tuberculosis, evolution of multi-drug resistant strains of the pathogen puts a large number of global populations at risk. Vaccine which can induce long-term protection is still in the making with many candidates currently in different phases of clinical trials. The COVID-19 pandemic has further aggravated the adversities by affecting early TB diagnosis and treatment. Yet, WHO remains adamant on its "End TB" strategy and aims to substantially reduce TB incidence and deaths by the year 2035. Such an ambitious goal would require a multi-sectoral approach which would greatly benefit from the latest computational advancements. To highlight the progress of these tools against TB, through this review, we summarize recent studies which have used advanced computational tools and algorithms for-early TB diagnosis, anti-mycobacterium drug discovery and in the designing of the next-generation of TB vaccines. At the end, we give an insight on other computational tools and Machine Learning approaches which have successfully been applied in biomedical research and discuss their prospects and applications against TB.

Universal Stress Proteins: From Gene to Function

Universal stress proteins (USPs) exist across a wide range of species and are vital for survival under stressful conditions. Due to the increasingly harsh global environmental conditions, it is increasingly important to study the role of USPs in achieving stress tolerance. This review discusses the role of USPs in organisms from three aspects: (1) organisms generally have multiple USP genes that play specific roles at different developmental periods of the organism, and, due to their ubiquity, USPs can be used as an important indicator to study species evolution; (2) a comparison of the structures of USPs reveals that they generally bind ATP or its analogs at similar sequence positions, which may underlie the regulatory role of USPs; and (3) the functions of USPs in species are diverse, and are generally directly related to the stress tolerance. In microorganisms, USPs are associated with cell membrane formation, whereas in plants they may act as protein chaperones or RNA chaperones to help plants withstand stress at the molecular level and may also interact with other proteins to regulate normal plant activities. This review will provide directions for future research, focusing on USPs to provide clues for the development of stress-tolerant crop varieties and for the generation of novel green pesticide formulations in agriculture, and to better understand the evolution of drug resistance in pathogenic microorganisms in medicine.

Mechanistic Insight into the Enzymatic Inhibition of β-Amyrin against Mycobacterial Rv1636: In Silico and In Vitro Approaches

Simple Summary

Rv1636 is a mycobacterial universal stress protein whose expression level increases in different type of stress conditions. This protein promotes the growth of Mycobacterium tuberculosis in the host derived stress conditions generated during infection. Therefore in this manuscipt, we are trying to target Rv1636 using natural inhibitor. Targeting essential Mycobacterial protein using natural prodect was hypothesized to generate a molecule with low toxic effects and high inhibitory activity. It was found that Rv1636 contains ATPase activity and its ATPase activity gets disturbed by addition of β-Amyrin in the reaction. β-Amyrin was forund to interfere with the ATP binding site of Rv1636 which was confirmed by molecular docking anad dynamic studies. In addition to the ATPase activity, Rv1636 was also contain the cAMP binding capacity and also involved in balancing the cAMP levels inside cells. So, targeting Rv1636 using β-Amyrin disrupts its ATPase activity and cAMP regulatory activity and these conditions might make Mycobacterium tuberculosis more susceptible to the host derived stress conditions.

Abstract

Mycobacterium tuberculosis has seen tremendous success as it has developed defenses to reside in host alveoli despite various host-related stress circumstances. Rv1636 is a universal stress protein contributing to mycobacterial survival in different host-derived stress conditions. Both ATP and cAMP can be bound with the Rv1636, and their binding actions are independent of one another. β-Amyrin, a triterpenoid compound, is abundant in medicinal plants and has many pharmacological properties and broad therapeutic potential. The current study uses biochemical, biophysical, and computational methods to define the binding of Rv1636 with β-Amyrin. A substantial interaction between β-Amyrin and Rv1636 was discovered by molecular docking studies, which helped decipher the critical residues involved in the binding process. VAL60 is a crucial residue found in the complexes of both Rv1636_β-Amyrin and Rv1636-ATP. Additionally, the Rv1636_β-Amyrin complex was shown to be stable by molecular dynamics simulation studies (MD), with minimal changes observed during the simulation. In silico observations were further complemented by in vitro assays. Successful cloning, expression, and purification of Rv1636 were accomplished using Ni-NTA affinity chromatography. The results of the ATPase activity assay indicated that Rv1636’s ATPase activity was inhibited in the presence of various β-Amyrin concentrations. Additionally, circular dichroism spectroscopy (CD) was used to examine modifications to Rv1636 secondary structure upon binding of β-Amyrin. Finally, isothermal titration calorimetry (ITC) advocated spontaneous binding of β-Amyrin with Rv1636 elucidating the thermodynamics of the Rv1636_β-Amyrin complex. Thus, the study establishes that β-Amyrin binds to Rv1636 with a significant affinity forming a stable complex and inhibiting its ATPase activity. The present study suggests that β-Amyrin might affect the functioning of Rv1636, which makes the bacterium vulnerable to different stress conditions.

'All That Glitters Is Not Gold': High-Resolution Crystal Structures of Ligand-Protein Complexes Need Not Always Represent Confident Binding Poses

Our understanding of the structure–function relationships of biomolecules and thereby applying it to drug discovery programs are substantially dependent on the availability of the structural information of ligand–protein complexes. However, the correct interpretation of the electron density of a small molecule bound to a crystal structure of a macromolecule is not trivial. Our analysis involving quality assessment of ~0.28 million small molecule–protein binding site pairs derived from crystal structures corresponding to ~66,000 PDB entries indicates that the majority (65%) of the pairs might need little (54%) or no (11%) attention. Out of the remaining 35% of pairs that need attention, 11% of the pairs (including structures with high/moderate resolution) pose serious concerns. Unfortunately, most users of crystal structures lack the training to evaluate the quality of a crystal structure against its experimental data and, in general, rely on the resolution as a ‘gold standard’ quality metric. Our work aims to sensitize the non-crystallographers that resolution, which is a global quality metric, need not be an accurate indicator of local structural quality. In this article, we demonstrate the use of several freely available tools that quantify local structural quality and are easy to use from a non-crystallographer’s perspective. We further propose a few solutions for consideration by the scientific community to promote quality research in structural biology and applied areas.