A centrin–Sfi1 myoneme fishnet powers ultrafast calcium-triggered contraction in the giant ciliate Spirostomum ambiguum
Year: 2026
Type: article
Abstract: Spirostomum is a giant unicellular ciliate that contracts to a quarter of its body length in less than five milliseconds, achieving an order of magnitude higher fractional shortening rate than actomyosin-based systems. This ultrafast contraction is powered by myonemes, calcium-activated protein networks at the cortex whose biochemical mechanism remains unclear. We quantify changes in cortical microtubules, membrane ruffles, and the fishnet-like myoneme mesh during contraction, and develop multiscale models that connect local myoneme shortening to whole-cell shape change. Centrin and an Sfi1 homolog colocalize with the myoneme by immunofluorescence and localize to the myoneme by immunogold electron microscopy. Coarse-grained mesh simulations reproduce the measured deformations and show that fishnet geometry, together with volume conservation, leads to uniform contraction. Finally, we reconstitute a Spirostomum centrin–Sfi1 repeat complex in vitro and measure calcium-dependent compaction and self-association, supporting a molecular basis for myoneme contractility. Together, these results underpin a multiscale model in which calcium-responsive centrin–Sfi1 structures are the central contractile element in Spirostomum and suggest design principles for fast, calcium-triggered, chemomechanical contractile networks that operate without actomyosin or ATP.
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: hybrid
Awards: Collaborative Research: Understanding and controlling force generation by a centrin-based contractile system, NNCI: North Carolina Research Triangle Nanotechnology Network (RTNN), G1676019983, G1907146399, G3275407028, G3338404878, Resource for Biocomputing Visualization and Informatics, G340396948, Fundamental principles, limits, and function of ultrafast motion in single cell organisms, Collaborative Research: CYBORG cells: Modular integration of synthetic organelles into living cells, G4815039349, G4882651412, Collaborative Research: Understanding and controlling force generation by a centrin-based contractile system, G5316600970, G5528850602, Collaborative Research: Understanding and controlling force generation by a centrin-based contractile system, G5973914729, Collaborative Research: CYBORG cells: Modular integration of synthetic organelles into living cells, G6810723037, Collaborative Research: Understanding and controlling force generation by a centrin-based contractile system, G9000001160, G9000063959, Biophysical mechanism and synthetic engineering of optically-controlled Ca2+-powered supramolecular engines
OpenAlex ID: W7162755774