Cryo-EM reveals how the mastigoneme assembles and responds to environmental signal changes

Y. Wang et al. present a high-resolution cryo-EM structure of the mastigoneme from Chlamydomonas reinhardtii flagella. The research provides insights into the mastigoneme's assembly mechanism and its potential roles in aiding adaptive responses to environmental changes, notably redox shifts and increased viscosity. Mastigonemes are thread-like structures adorning the flagella of protists. In Chlamydomonas reinhardtii, filamentous mastigonemes find their roots in the flagella's distal region, associated with the channel protein PKD2, implying their potential contribution to external signal sensing and flagellar motility control. Here, we present the single-particle cryo-electron microscopy structure of the mastigoneme at 3.4 angstrom. The filament unit, MST1, consists of nine immunoglobulin-like domains and six Sushi domains, trailed by an elastic polyproline-II helix. Our structure demonstrates that MST1 subunits are periodically assembled to form a centrosymmetric, non-polar filament. Intriguingly, numerous clustered disulfide bonds within a ladder-like spiral configuration underscore structural resilience. While defects in the mastigoneme structure did not noticeably affect general attributes of cell swimming, they did impact specific swimming properties, particularly under varied environmental conditions such as redox shifts and heightened viscosity. Our findings illuminate the potential role of mastigonemes in flagellar motility and suggest their involvement in diverse environmental responses.

Automated summary

This study presents a high-resolution cryo-EM structure of mastigonemes from Chlamydomonas reinhardtii flagella and provides insights into their assembly mechanism and potential roles in adaptive responses. The mastigoneme structure affects specific swimming properties under varied environmental conditions. These findings illuminate the potential role of mastigonemes in flagellar motility and environmental responses.