Biology subjects

BALASUBRAMANIAN, M.

Publications and source records attributed to BALASUBRAMANIAN, M..

4 recordsLinked to original sources

bioRxiv2026

Comparative Modelling of Actin-Tropomyosin Interfaces

Tropomyosins are coiled-coil dimers that polymerize head-to-tail along actin filaments. They stabilize distinct filament populations and regulate the access of myosins and actin-binding proteins in both muscle and non-muscle contexts. Despite their central regulatory role, how filament length and isoform identity of different tropomyosin homologues might modulate actin affinity is not completely understood, especially across species. Here, we present a stepwise computational docking pipeline combining AlphaFold2-Multimer coiled-coil models, experimentally informed residue-level restraints, and pseudo-energy analysis via PPCheck to build and evaluate actin-tropomyosin co-polymer models for three isoforms: human TPM1 (hTPM1; 284 residues), human TPM4 (hTPM4; 248 residues), and Schizosaccharomyces pombe Cdc8 (SpCdc8; 161 residues). Interface energetics reveal a consistent hierarchy in which the shortest filament, SpCdc8, achieves the most stabilizing and residue-rich actin contacts, consistent with reduced cumulative geometric penalty along the actin helix. Among human isoforms, hTPM1 forms stronger interfaces with actin than hTPM4. The hTPM1-actin model also exhibits higher contact density and additional energetic hotspots, in agreement with the experimentally established slower exchange kinetics of TPM1 isoforms on actin filaments relative to TPM4. Hotspot mapping identifies conserved acidic residues at equivalent positions across all three isoforms, emphasizing the importance of electrostatic anchor points in maintaining interface integrity across diverse evolutionary contexts. Modeling of four temperature-sensitive SpCdc8 mutations (A18T, R21H, E31K and E129K) reveals that these substitutions substantially destabilize the coiled-coil dimer without significantly affecting actin interactions, suggesting that subtle regulatory failure arises from compromised longitudinal cable continuity rather than from direct loss of actin affinity. Taken together, our results support a hierarchical model of tropomyosin dimer stability, actin-tropomyosin recognition in which filament length imposes a geometric baseline on interface stability, onto which isoform-specific sequence evolution superimposes functional tuning. The tropomyosin homologues we studied appear to retain conserved electrostatic hotspots thereby providing a common structural scaffold across tissues and organisms.

bioinformatics↗

bioRxiv2022

Fission yeast Smi1p participates in the synthesis of the primary septum by regulating β-1,3-glucan synthase Bgs1p function

Cytokinesis is the concluding step of the cell cycle. Coordination between multiple cellular processes is essential for the success of cytokinesis. The fission yeast, Schizosaccharomyces pombe, like other fungal cells is contained within a cell wall. During cell division, the external cell wall is extended inwards to form a special septum wall structure in continuity with the cell wall. The primary septum, the central component of the three-layered division septum, is enriched with linear {beta}-1,3-glucan formed by Bgs1p, a {beta}-1,3-glucan synthase. In this study we uncover a novel essential protein, Smi1p, that functions as a suppressor of the Bgs1p temperature-sensitive mutant, cps1-191. We observe a rescue in the cell wall composition and ultrastructure and also in actomyosin ring dynamics. Further, we identify a colocalization and physical association between Bgs1p and Smi1p. Altogether, our results indicate that Smi1p regulates the function of Bgs1p during cytokinesis.

cell biology↗

bioRxiv2021

Myosin turnover controls actomyosin contractile instability

Actomyosin contractile force is harnessed for diverse functions, from cell division to morphogenesis during development. However, actomyosin contractility is intrinsically unstable to self-reinforcing spatial variations that destroy actomyosin architecture if unopposed. The full instability was rarely observed, and how cells control the instability is not established. Here, we observed the instability run its full course in isolated cytokinetic contractile rings lacking component turnover. Myosin II aggregated hierarchically into aggregates of growing size and separation up to a maximum. Molecularly explicit simulations reproduced hierarchical aggregation that precipitated tension loss and ring fracture, and identified the maximum separation as the length of actin filaments mediating mechanical communication between aggregates. Late stage simulated aggregates had aster-like morphology with polarity sorted actin, similar to late stage actomyosin systems in vitro. Our results suggest myosin II turnover controls actomyosin contractile instability in normal cells, setting myosin aggregate size and intercepting catastrophic hierarchical aggregation and fracture.

cell biology↗

bioRxiv2020

Genetic interaction between profilin and myosin II reveals a potential role for myosin II in actin filament disassembly in vivo

The actin cytoskeleton plays a variety of roles in eukaryotic cell physiology, ranging from cell polarity and migration to cytokinesis. Key to the function of the actin cytoskeleton is the mechanisms that control its assembly, stability, and turnover. Through genetic analyses in fission yeast, we found that, myo2-S1 (myo2-G515D), a myosin II mutant allele was capable of rescuing lethality caused by compromise of mechanisms involved in actin cable / ring assembly and stability. The mutation in myo2-S1 affects the activation loop of Myosin II, which is involved in physical interaction with subdomain 1 of actin and in stimulating the ATPase activity of Myosin. Consistently, actomyosin rings in myo2-S1 cell ghosts were severely compromised in contraction upon ATP addition, suggesting that Myo2-S1p was defective in actin binding and / or motor activity. These studies strongly suggest a role for Myo2p in actin cytoskeletal disassembly and turnover, and that compromise of this activity leads to genetic suppression of mutants defective in actin cable assembly / stability.

cell biology↗