Biology subjects

Tetlalmatzi, S. C.

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

2 recordsLinked to original sources

bioRxiv2025

Conformational flexibility of tubulin dimers regulates the transitions of microtubule dynamic instability

Microtubules are highly conserved polymers of {beta}-tubulin dimers that undergo dynamic instability. While dynamic instability is conserved across eukaryotes, many of its associated conformational changes, like lattice compaction and twist, are not. Tubulin dimers sample multiple conformations in solution and undergo conformational changes during polymerization; the rate and extent of these changes describes their "conformational flexibility." Here, we investigate the relationship between the conformational flexibility of tubulins and the dynamic phenotypes of the microtubules they produce with a comparative study of Drosophila melanogaster tubulin (Dm-Tb) and Bos taurus brain tubulin (Bt-Tb). While these tubulins share high sequence and structural similarity, their microtubules display divergent dynamic phenotypes in vitro, with altered transition frequencies between phases of growth and shrinkage. Dm-Tb microtubules showed drastically longer lifetimes, lower barriers to nucleation, and a high rescue frequency, while maintaining a similar growth rate to Bt-Tb microtubules. 3D reconstruction of mature Dm-Tb microtubules showed high structural conservation with mammalian microtubules. However, when we performed molecular dynamics simulations of free tubulin dimers, we found Dm-Tb to be more rigid and adopt fewer conformational states than Bt-Tb. Biochemical characterizations experimentally confirmed this finding, leading us to hypothesize that differences in the conformational flexibility of tubulins may tune the frequency of transitions between the dynamic phases of microtubules, thereby altering their stability and overall dynamic phenotypes.

biophysics↗

bioRxiv2024

Microtubule dynamic instability is sensitive to specific biological viscogens in vitro

Cytoplasm is a viscous, crowded, and heterogeneous environment, and its local viscosity and degree of macromolecular crowding have significant effects on cellular reaction rates. Increasing viscosity slows down diffusion and protein conformational changes, while increasing macromolecular crowding speeds up reactions. As a model system for cellular reactions, microtubule dynamics are slowed down in vivo when cytoplasm concentration is increased by osmotic shifts, indicating a dominant role for viscosity in microtubule reaction pathways. In the cell, viscosity is determined by diverse species of "biological viscogens", including glycerol, trehalose, intermediate metabolites, proteins, polymers, organelles, and condensates. Here we show in vitro that microtubule dynamic instability is sensitive to specific viscogen species, particularly glycerol. We found that increasing viscosity with glycerol or trehalose slowed microtubule growth, slowed microtubule shrinkage, and increased microtubule lifetimes, similar to the "freezing" observed previously in vivo. Increasing viscosity with a globular protein, bovine serum albumin, increased microtubule growth rates, as its viscous effects may be balanced against its macromolecular crowding effects. At matched viscosities, glycerol had an outsized effect on microtubule lifetimes, rescues, and nucleation compared to other viscogens. Increasing viscosity did not, however, increase the intensity of EB3-GFP comets, indicating that GTP hydrolysis is unaffected by buffer conditions. We propose that glycerol exerts its distinct effect on microtubule dynamic instability by stabilizing the microtubule lattice after phosphate release. Effects of specific viscogens may modulate many cellular reaction rates within local environments of cytoplasm.

biochemistry↗