Biology subjects

Cohan, M. C.

Publications and source records attributed to Cohan, M. C..

3 recordsLinked to original sources

bioRxiv2022

Connecting sequence features within the disordered C-terminal linker of B. subtilis FtsZ to function and bacterial cell division

Intrinsically disordered regions (IDRs) can function as autoregulators of folded enzymes to which they are tethered. One example is the bacterial cell division protein, FtsZ. This includes a folded core and a C-terminal tail (CTT) that encompasses a poorly conserved, disordered C-terminal linker (CTL) and a well-conserved 17-residue C-terminal peptide (CT17). Sites for GTPase activity of FtsZs are formed at the interface between GTP binding sites and T7 loops on cores of adjacent subunits within dimers. Here, we explore the basis of autoregulatory functions of the CTT in Bacillus subtilis FtsZ (Bs-FtsZ). Molecular simulations show that the CT17 of Bs- FtsZ makes statistically significant CTL-mediated contacts with the T7 loop. Statistical Coupling Analysis of more than 103 sequences from FtsZ orthologs reveals clear covariation of the T7 loop and the CT17 with most of the core domain whereas the CTL is under independent selection. Despite this, we discover the conservation of non-random sequence patterns within CTLs across orthologs. To test how the non-random patterns of CTLs mediate CTT-core interactions and modulate FtsZ functionalities, we designed Bs-FtsZ variants by altering the patterning of oppositely charged residues within the CTL. Such alterations disrupt the core-CTT interactions, lead to anomalous assembly and inefficient GTP hydrolysis in vitro and protein degradation, aberrant assembly, and disruption of cell division in vivo. Our findings suggest that viable CTLs in FtsZs are likely to be IDRs that encompass non-random, functionally relevant sequence patterns that also preserve three-way covariation of the CT17, the T7 loop, and core domain. Significance StatementZ-ring formation by the protein FtsZ controls cell division in rod-shaped bacteria. The C-terminus of FtsZ encompasses a disordered C-terminal linker (CTL) and a conserved CT17 motif. Both modules are essential for Z-ring formation and proper localization of FtsZ in cells. Previous studies suggested that generic intrinsically disordered regions (IDRs) might be suitable functional replacements for naturally occurring CTLs. Contrary to this suggestion, we find that the sequence-encoded conformational properties of CTLs help mediate autoregulatory interactions between covarying regions within FtsZ. Functional properties of the CTL are encoded via evolutionarily conserved, non-random sequence patterns. Disruption of these patterns impair molecular functions and cellular phenotypes. Our findings have broad implications for discovering functionally consequential sequence features within IDRs of other proteins.

biophysics↗

bioRxiv2021

Uncovering non-random sequence patterns within intrinsically disordered proteins

Sequence-ensemble relationships of intrinsically disordered proteins (IDPs) are governed by binary patterns such as the linear clustering or mixing of specific residues or residue types with respect to one another. To enable the discovery of potentially important, shared patterns across sequence families, we describe a computational method referred to as NARDINI for Non-random Arrangement of Residues in Disordered Regions Inferred using Numerical Intermixing. This work was partially motivated by the observation that parameters that are currently in use for describing different binary patterns are not interoperable across IDPs of different amino acid compositions and lengths. In NARDINI, we generate an ensemble of scrambled sequences to set up a composition-specific null model for the patterning parameters of interest. We then compute a series of pattern-specific z-scores to quantify how each pattern deviates from a null model for the IDP of interest. The z-scores help in identifying putative non-random linear sequence patterns within an IDP. We demonstrate the use of NARDINI derived z-scores by identifying sequence patterns in three well-studied IDP systems. We also demonstrate how NARDINI can be deployed to study archetypal IDPs across homologs and orthologs. Overall, NARDINI is likely to aid in designing novel IDPs with a view toward engineering new sequence-function relationships or uncovering cryptic ones. We further propose that the z-scores introduced here are likely to be useful for theoretical and computational descriptions of sequence-ensemble relationships across IDPs of different compositions and lengths.

biophysics↗

bioRxiv2018

Evolved sequence features within the intrinsically disordered tail influence FtsZ assembly and bacterial cell division

Intrinsically disordered regions (IDRs) challenge the well-established sequence-structure-function paradigm for describing protein function and evolution. Here, we direct a combination of biophysical and cellular studies to further our understanding of how the intrinsically disordered C-terminal tail of FtsZ contributes to cell division in rod-shaped bacteria. FtsZ is a modular protein that encompasses a conserved GTPase domain and a highly variable intrinsically disordered C-terminal tail (CTT). The CTT is essential for forming the cytokinetic Z-ring. Despite poor sequence conservation of the CTT, the patterning of oppositely charged residues, which refers to the extent of linear mixing / segregation of oppositely charged residues within CTT sequences is bounded within a narrow range. To assess the impact of evolutionary bounds on charge patterning within CTT sequences we performed experiments, aided by sequence design, to quantify the impact of changing the patterning of oppositely charged residues within the CTT on the functions of FtsZ from B. subtilis. Z-ring formation is robust if and only if the extent of linear mixing / segregation of oppositely charged residues within the CTT sequences is within evolutionarily observed bounds. Otherwise, aberrant, CTT-mediated, FtsZ assemblies impair Z-ring formation. The complexities of CTT sequences also have to be above a threshold value because FtsZ variants with low complexity CTTs are not tolerated in cells. Taken together, our results suggest that CTT sequences have evolved to be \"just right\" and that this is achieved through an optimal extent of charge patterning while maintaining the sequence complexity above a threshold value.

biophysics↗