Biology subjects

Bihani, S. C.

Publications and source records attributed to Bihani, S. C..

3 recordsLinked to original sources

bioRxiv2026

Expanding the GUSome: Structure-guided identification and characterization of gut microbial β-glucuronidases

The gut microbiome-encoded {beta}-glucuronidase (GUS) enzymes have a significant effect on human physiology through their deglucuronidation activity on endogenous and exogenous glucuronides. GUS activity also significantly influences the pharmacokinetics, efficacy and toxicity of various drugs including chemotherapeutic drugs. Given their crucial role in drug metabolism, GUS enzymes have emerged as promising targets for therapeutic intervention. Here, we have identified and characterized 79 unique GUS enzymes through a structure-guided approach. Structural modelling of these GUS enzymes revealed a conserved core and active-site residues with significant variations in the number and nature of the C-terminal domains. A new classification system based on the number and type of additional C-terminal domains is presented for the GUS proteins. Further, GUS enzymes have been categorized into different loop categories linked to their substrate preferences. The relationship between domain architecture and loop-type is explored by sequence similarity network analysis. We could successfully express, purify and validate GUS processing capability of a panel of identified GUS proteins. The nature of oligomer organization has been deciphered by SEC and DLS studies. Further, we have identified additional GUS enzymes capable of processing SN-38G, glucuronidated form of anticancer drug, irinotecan. These newly identified GUS enzymes will offer valuable insights into gut microbial GUS diversity and their role in understanding the population-specific drug-induced adverse effects on human health.

bioinformatics↗

bioRxiv2021

Molecular Basis for Reduced Cleavage Activity and Drug Resistance in D30N HIV-1 protease

Nelfinavir is one of the FDA approved HIV-1 protease inhibitors and is a part of HAART therapy for the treatment of HIV-AIDS. Nelfinavir was the first HIV-1 protease inhibitor to be approved as a Paediatric formulation. The application of HAART had resulted into significant improvement in the life of AIDS patients. However, emergence of drug resistance in HIV-1 protease limited the use of many of these drugs including nelfinavir. A unique mutation observed frequently in patients treated with nelfinavir is D30N as it is selected exclusively by nelfinavir. It imparts very high resistance to nelfinavir but unlike other primary mutations does not give cross resistance to the majority of other drugs. D30N mutation also significantly reduces cleavage activity of HIV-1 protease and affects the viral fitness. Here, we have determined structures of D30N HIV-1 protease in unliganded form and in complex with the drug nelfinavir. These structures provide rationale for reduced cleavage activity and molecular basis of resistance induced by D30N mutation. The loss of coulombic interaction part of a crucial hydrogen bond between the drug and the enzyme, is a likely explanation for reduced affinity and drug resistance towards nelfinavir. The decreased catalytic activity of D30N HIV protease, due to altered interaction with substrates and reduced stability of folding core may be the reasons for reduced replicative capacity of the HIV harboring D30N HIV-1 protease.

molecular biology↗

bioRxiv2020

WD 40 domain of RqkA regulates its kinase activity and role in extraordinary radioresistance in Deinococcus radiodurans

RqkA, a DNA damage responsive Serine / Threonine kinase is characterized for its role in DNA repair and cell division in D. radiodurans. It has a unique combination of a kinase domain at N-terminus and a WD40 type domain at C-terminus joined through a linker. WD40 domain is comprised of eight {beta} propeller repeats held together via "tryptophan-docking motifs" and forming a typical velcro closure structure. RqkA mutants lacking the WD40 region (hereafter referred to as WD mutant) could not complement RqkA loss in {gamma} radiation resistance in D. radiodurans and lacked {gamma} radiation mediated activation of kinase activity in vivo. WD mutants failed to phosphorylate its cognate substrate (e.g. DrRecA) in surrogate E. coli cells. Further, unlike wild type enzyme, the kinase activity of its WD40 mutants was not stimulated by Pyrroloquinoline quinine (PQQ) indicating the role of the WD motifs in PQQ interaction and stimulation of its kinase activity. Together, results highlighted the importance of the WD40 domain in the regulation of RqkA kinase signaling functions in vivo and thus the role of WD40 domain in the regulation of any STPK is the first time demonstrated in bacteria. ImportanceThis study highlights the importance of the WD40 domain in activity regulation and signaling activity of bacterial serine/ threonine kinase for the first time in the bacterial response to gamma radiation and DNA damage.

molecular biology↗