Biology subjects

Taoka, A.

Publications and source records attributed to Taoka, A..

3 recordsLinked to original sources

bioRxiv2025

Magnetosome organelles are organized through interactions between McaA and McaB that alter the dynamics of the bacterial actin-like protein MamK

Magnetotactic bacteria (MTB) are a group of Gram-negative species that produce a lipid-bounded organelle, the magnetosome, in which a magnetic crystal is biomineralized. MTB use magnetosomes to align with the geomagnetic field for improved navigation of their environment. To optimize this alignment, these species organize their magnetosomes in a linear fashion using a handful of factors including the bacterial actin-like protein MamK. Despite these shared features, there is a broad diversity of species-specific linear magnetosome chain arrangements within MTB, but the molecular mechanisms behind these phenotypic variations are unclear. Recently, genetic analyses showed that two proteins McaA and McaB interface with the chain organization machinery of Magnetospirillum magneticum AMB-to arrange magnetite crystals in a series of subchains rather than the single cohesive chains found in closely related MTB. Here, we use in vivo co-immunoprecipitation in AMB-1 to demonstrate protein-protein interactions between McaA, McaB, and MamK. Experiments with McaA truncation mutants and conditional control of McaB localization determined that McaA-McaB interactions are dependent on amino acids 530-665 of McaA and McaB localization to the magnetosome chain. We further show that disrupting the McaA-McaB interaction alters the spatial dynamics of MamK in vivo We present a model in which protein-protein interactions between McaA, McaB, and MamK drive changes in MamK behavior to establish AMB-1s magnetosome chain organization. IMPORTANCEMagnetosomes model for understanding the cell biology of bacterial organelles and the mechanisms of bacterial cell organization. MamK, one of the best-studied bacterial actins, is a notable player in magnetosome chain assembly. This work explores how MamK dynamics are altered by two potential bacterial actin binding proteins, McaA and McaB. This system illustrates how changes in bacterial cytoskeleton regulation result in different organization of subcellular compartments. The conclusions from this research also have implications for understanding the broader evolutionary strategies for regulation of actin-like proteins and compartment organization diversification in bacteria.

microbiology↗

bioRxiv2023

S100A11 promotes focal adhesion disassembly via myosin II-driven contractility and Piezo1-mediated Ca2+ entry

S100A11 is a small Ca2+-activatable protein with an established role in different cellular processes involving actin cytoskeleton remodeling, such as cell migration, membrane protrusion formation, and plasma membrane repair. It also displays Ca2+-dependent F-actin binding activity and localizes to actin stress fibers (SFs), but its precise role in regulating these structures remains unclear. Analyzing endogenous S100A11 localization in HeLa and U2OS osteosarcoma cells confirmed SF association but in addition revealed steady localization to stable focal adhesions (FAs), typically at the end of dorsal stress fibers. In contrast, S100A11 levels at FAs increased sharply, but transiently, at the onset of peripheral FA disassembly. Elevating intracellular Ca2+ levels using the Ca2+ ionophore ionomycin reliably stimulated both S100A11 recruitment and subsequent FA disassembly. However, pre-incubation with the non-muscle myosin II (NM II) inhibitor blebbistatin, or with an inhibitor to the stretch-activatable Ca2+ channel Piezo1 effectively suppressed S100A11 recruitment, implicating S100A11 in an actomyosin contractility-driven FA disassembly mechanism involving Piezo1-dependent Ca2+ influx. Applying external mechanical forces on peripheral FAs via a micropipette likewise recruited S100A11 to FAs, even when NM II was inhibited by blebbistatin or in NM IIA knockout cells, corroborating the mechanosensitive recruitment mechanism of S100A11. However, extracellular Ca2+ and Piezo1 function was still indispensable, indicating that NM II-dependent contraction forces act upstream of Piezo1-mediated Ca2+ influx, in turn leading to S100A11 activation and FA recruitment. Moreover, S100A11 knockout cells feature enlarged FAs and display delayed FA disassembly during cell membrane retraction, consistent with impaired FA turnover in these cells. Our results thus demonstrate a novel mechano-sensitive function for S100A11 in promoting actomyosin contractility-driven FA disassembly.

cell biology↗

bioRxiv2022

McaA and McaB control the dynamic positioning of a bacterial magnetic organelle

Magnetotactic bacteria (MTB) are a diverse group of microorganisms that use intracellular chains of ferrimagnetic nanocrystals, produced within their magnetosome organelles, to align and navigate along the geomagnetic field. The cell biological and biochemical properties of magnetosomes make them a powerful model for studying the molecular mechanisms of biomineralization and compartmentalization in bacteria. While several conserved magnetosome formation genes have been described, the evolutionary strategies for their species-specific diversification remain unknown. Here, we demonstrate that the fragmented nature of magnetosome chains in Magnetospirillum magneticum AMB-1 is controlled by two genes named mcaA and mcaB. McaA recognizes the positive curvature of the inner cell membrane while McaB localises to magnetosomes. Along with the MamK actin-like cytoskeleton, they create space for addition of new magnetosomes in between pre-existing magnetosomes. Phylogenetic analyses suggest that McaAB homologs are widespread and may represent an ancient strategy for organelle positioning in MTB.

microbiology↗