Biology subjects

Chattopadhyay, G.

Publications and source records attributed to Chattopadhyay, G..

5 recordsLinked to original sources

bioRxiv2026

Negative Autoregulation Promotes the Evolution of Strong Environmental Switching

Living systems rely on gene regulatory circuits to respond to environmental change. Such circuits often act as molecular switches: OFF in the absence of a cue, and ON in its presence. We do not know how a circuits regulatory architecture affect its ability to evolve such responsiveness. In nature, a very frequent and simple regulatory architecture involves a transcriptional regulator that negatively regulates its own expression. To study how such autoregulation affects adaptive evolution, we engineered E. coli circuits in which a target gene is regulated by the repressor TetR with (A-) or without (A0) negative autoregulation of TetR. We evolved TetR in both architectures toward responsiveness to a novel environment, embodied by a novel inducer of TetR. Early during their evolution, TetR circuits with negative autoregulation evolved stronger environmental switching. A combination of high throughput DNA sequencing, protein engineering, and biophysical modeling showed why. Only A-circuits favored TetR alleles that interact strongly with both the inducer and DNA. Such alleles combine strong repression caused by strong DNA binding with strong derepression caused by strong inducer binding, the defining property of a strong environmental response. Our biophysical model shows that negative autoregulation helps to create this regulatory regime. As a result, only A- circuits favor alleles that create strong molecular switches. Altogether, our work shows that even the simplest form of gene regulation can change the topography of a fitness landscape, and enable new modes of evolutionary change.

evolutionary biology↗

bioRxiv2025

The fitness landscape of the E.coli lac operator is highly rugged in two different environments

We know little about the fitness landscapes of bacterial operators, regulatory DNA elements that are crucial to regulate metabolic genes like those of the lac operon for lactose utilization. For example, we do not know whether adaptive evolution could easily create strong operators from weak ones or from non-regulatory DNA. To find out, we used CRISPR-Cas-assisted genome editing, bulk competition, and high-throughput sequencing to map the fitness landscape of more than 140,000 lac operator variants in two chemical environments that harbor lactose or glycerol as sole carbon sources. Both landscapes are highly rugged and contain thousands of fitness peaks, which allow only 2 percent of evolving populations to reach a high fitness peak. The landscapes share only 15 percent of fitness peaks. Our work illustrates that landscape ruggedness caused by epistasis can represent an important obstacle to adaptive evolution of regulatory sequences. It also shows that a simple environmental change can substantially affect fitness landscape topography.

evolutionary biology↗

bioRxiv2022

Ter-Seq: A high-throughput method to stabilize transient ternary complexes and measure associated kinetics

Regulation of biological processes by proteins often involves the formation of transient, multimeric complexes whose characterisation is mechanistically important but challenging. The bacterial toxin CcdB binds and poisons DNA Gyrase. The corresponding antitoxin CcdA extracts CcdB from its complex with Gyrase through formation of a transient ternary complex, thus rejuvenating Gyrase. We describe a high throughput methodology called Ter-Seq to stabilize probable ternary complexes and measure associated kinetics using the CcdA-CcdB-GyrA14 ternary complex as a model system. The method involves screening a YSD saturation mutagenesis library of one partner (CcdB) for mutants that show enhanced ternary complex formation. We also isolated CcdB mutants that were either resistant or sensitive to rejuvenation, and used SPR with purified proteins to validate the kinetics measured using surface display. Positions where CcdB mutations lead to slower rejuvenation rates are largely involved in CcdA-binding, though there were several notable exceptions. Mutations at these positions reduce the affinity towards CcdA, thereby slowing down the rejuvenation process. Mutations at GyrA14-interacting positions significantly enhanced rejuvenation rates, either due to reduced affinity or complete loss of CcdB binding to GyrA14. We examined the effect of different parameters (CcdA affinity, GyrA14 affinity, surface accessibilities, evolutionary conservation) on the rate of rejuvenation. Finally, we further validated the Ter-Seq results by monitoring kinetics of ternary complex formation for individual CcdB mutants in solution by FRET studies.

biophysics↗

bioRxiv2021

Mechanistic insights into global suppressors of protein folding defects

Most amino acid substitutions in a protein either lead to partial loss of function or are near neutral. Several studies have shown the existence of second-site mutations that can rescue defects caused by diverse loss of function mutations. Such global suppressor mutations are key drivers of protein evolution. However, the mechanisms responsible for such suppression remain poorly understood. To address this, we characterized multiple suppressor mutations both in isolation and in combination with inactive mutants. We examined six global suppressors of the bacterial toxin CcdB, the known M182T global suppressor of TEM-1 {beta}-lactamase, the N239Y global suppressor of p53-DBD and three suppressors of the SARS-CoV-2 spike Receptor Binding Domain. The suppressors both alone, and in conjunction with inactive mutants, stabilise the protein both thermodynamically and kinetically in-vitro, predominantly through acceleration of the refolding rate. When coupled to inactive mutants they promote increased in-vivo solubilities as well as regain-of-function phenotypes. In the case of CcdB, where novel suppressors were isolated, we determined the crystal structures of three such suppressors to obtain insight into the specific molecular interactions responsible for the observed effects. While most individual suppressors result in small stability enhancements relative to wildtype, which can be combined to yield significant stability increases, thermodynamic stabilisation is neither necessary nor sufficient for suppressor action.

biophysics↗

bioRxiv2018

Combating viral contaminants in CHO cells by engineering STAT1 mediated innate immunity

Viral contamination in biopharmaceutical manufacturing can lead to shortages in the supply of critical therapeutics. To facilitate the protection of bioprocesses, we explored the basis for the susceptibility of CHO cells, the most commonly used cell line in biomanufacturing, to RNA virus infection. Upon infection with certain ssRNA and dsRNA viruses, CHO cells fail to generate a significant interferon (IFN) response. Nonetheless, the downstream machinery for generating IFN responses and its antiviral activity is intact in these cells: treatment of cells with exogenously-added type I IFN or poly I:C prior to infection limited the cytopathic effect from Vesicular stomatitis virus (VSV), Encephalomyocarditis virus (EMCV), and Reovirus-3 virus (Reo-3) in a STAT1-dependent manner. To harness the intrinsic antiviral mechanism, we used RNA-Seq to identify two upstream repressors of STAT1: Gfi1 and Trim24. By knocking out these genes, the engineered CHO cells exhibited increased resistance to the prototype RNA viruses tested. Thus, omics-guided engineering of mammalian cell culture can be deployed to increase safety in biotherapeutic protein production among many other biomedical applications.

bioengineering↗