Biology subjects

Amritkar, K.

Publications and source records attributed to Amritkar, K..

4 recordsLinked to original sources

bioRxiv2024

Nitrogenase structural evolution across Earth s history

Life on Earth is about 4 billion years old--nearly as old as the planet itself. Over this immense timespan, living systems and their biomolecules have both adapted to and driven profound changes in the Earths environment. Among these, certain critical enzymes emerged early and have persisted through planetary extremes. Here, we implement an integrated approach to investigate the structural evolution of nitrogenase, an ancient and globally essential enzyme responsible for biological nitrogen fixation. Despite the ecological diversity of its host microbes, nitrogenase retains strict functional constraints, including extreme oxygen sensitivity, high energy demands, and substrate availability. We combined phylogenetics, ancestral sequence reconstruction, protein crystallography and deep-learning based structural prediction to resurrect nearly three billion years of nitrogenase structural history. This effort represents the first effort to predict the full set of extant and ancestral structures along the evolutionary tree of a single enzyme, yielding over 5000 structural models. Our framework lays a foundation for reconstructing key structural constraints that shape protein evolution and examining ancient enzymes within the broader context of phylogenetic relationships and environmental transitions across geological timescales.

evolutionary biology↗

bioRxiv2024

Molecular and structural innovations of the stator motor complex at the dawn of flagellar motility

The rotation of the bacterial flagellum is powered by the MotAB stator complex, which converts ion flux into torque. The origin and evolution of this remarkable complex is understudied. Here, we perform the first phylogenetic and structural characterisation and classification of MotAB and nonflagellar relatives. Using 193 genomes sampled across 27 bacterial phyla, we estimated phylogenies and ancestral sequences, and generated AlphaFold predictions for all extant and reconstructed proteins. We then mapped them onto the phylogeny to determine patterns of diversity and distribution of structural innovations. We identify two discrete groups: the Flagellar Ion Transporters (FIT) and the Generic Ion Transporters (GIT). The FIT proteins are structurally conserved and have a square fold domain and a torque-generating interface (TGI). FIT proteins are divided into two clades, termed TGI4 and TGI5, referring to whether there have 4 or 5 short helices in the TGI. TGI5 motors are predominantly found in Proteobacteria and include the well-studied E. coli K12 system, while TGI4 motors are found in diverse phyla and include the Na+-powered polar motors of Vibrio (PomAB). The GIT proteins, on the other hand, are structurally diverse and lack these attributes. The interaction between the A and B subunits is conserved across the FIT and GIT proteins. The two subunits are jointly necessary for function, with the genes typically adjacent within an operon. Motility assays in E. coli show that the structural elements unique to FIT play an important role in flagellar motility. Our results indicate that the stator motor complex has a single origin and shares unique motility-related structural traits. Significance StatementFlagellar motility is a key feature in bacterial pathogenicity and survival. It allows bacteria to propel themselves and direct movement according to environmental conditions. We investigated the molecular and structural diversity of the stator motor proteins that provide the ion motive force to power flagellar rotation. This study integrates phylogenetics, 3D protein structure modeling, motility assays and ancestral state reconstruction (ASR) to provide insights into the structural mechanisms that first powered the flagellar motor. We provide the first phylogenetic and structural characterisation and classification of MotAB and relatives.

evolutionary biology↗

bioRxiv2024

Ancestral structure prediction reveals the conformational impact of the RuBisCO small subunit across time

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is an ancient protein critical for CO2-fixation and global biogeochemistry. Form-I RuBisCO complexes uniquely harbor small subunits that form a hexadecameric complex together with their large subunits. The small subunit protein is thought to have significantly contributed to RuBisCOs response to the atmospheric rise of O2 [~]2.5 billion years ago, marking a pivotal point in the enzymes evolutionary history. Here, we performed a comprehensive evolutionary analysis of extant and ancestral RuBisCO sequences and structures to explore the impact of the small subunits earliest integration on the molecular dynamics of the overall complex. Our simulations suggest that the small subunit restricted the conformational flexibility of the large subunit early in its history, impacting the evolutionary trajectory of the Form-I RuBisCO complex. Molecular dynamics investigations of CO2 and O2 gas distribution around predicted ancient RuBisCO complexes suggest that a proposed "CO2 reservoir" role for the small subunit is not conserved throughout the enzymes evolutionary history. The evolutionary and biophysical response of RuBisCO to changing atmospheric conditions on ancient Earth showcase multi-level and trackable responses of enzymes to environmental shifts over long timescales.

evolutionary biology↗

bioRxiv2019

Predicting and Designing therapeutics against the Nipah virus

Though every outbreak of the Nipah Virus has resulted in high mortality rates (>70% in Southeast Asia), there are no licensed drugs against it. In this study we have considered all 9 Nipah proteins as potential therapeutic targets and computationally identified putative peptides (against G, F, and M proteins) and small molecules inhibitors (against F, G, M, N, and P proteins). The computations include extensive homology/ab initio modelling, peptide design and small molecule docking. An important contribution of this study is the increased structural characterization of Nipah proteins by approximately 90% of what is deposited in the PDB. In addition, we have carried out molecular dynamics simulations on all the designed protein-peptide complexes to check for stability and to estimate binding strengths. Details, including atomic coordinates of all the proteins and their ligand bound complexes, can be accessed at http://cospi.iiserpune.ac.in/Nipah. Our strategy was to tackle the development of therapeutics on a proteome wide scale and the lead compounds identified could be attractive starting points for drug development. To this end, we have designed 4 peptide inhibitors and predicted 70 small molecules (13 with high confidence) against 3 and 5 Nipah proteins respectively. To counter the threat of drug resistance, we have analyzed the sequences of the viral strains from different outbreaks, to check whether they would be sensitive to the binding of the proposed inhibitors.\n\nAuthor SummaryNipah virus infections have killed 72-86% of the infected individuals in Bangladesh and India. The infections are spread via bodily secretions of bats, pigs and other infected individuals. Even though, the disease was first detected in the human population in 1998, there are no approved drugs/vaccines against it. In this study, we have tried to model the 3D structures of the Nipah virus proteins. We have then used these models to design/predict small inhibitory molecules that would bind them and prevent their function. We have also analyzed the different strains of the virus to identify conservation patterns of amino acids in the proteins, which in turn informs us of the efficacy of the drugs. The designed/docked compounds as well as the protein models are freely accessible for experimental validation and hypothesis testing.

bioinformatics↗