Morphology of the archaellar motor and associated cytoplasmic cone in Thermococcus kodakaraensis.

Ariane Briegel,Dorothy Kenny,Audrey N Huang,Grant J Jensen,Hong H Nguyen,Debnath Ghosal,Yi‐Wei Chang,Ki Woo Kim,Robert P Gunsalus,Rachel R Ogorzalek Loo,Catherine M Oikonomou,Andreas Kjær

doi:10.15252/embr.201744070

Abstract

Archaeal swimming motility is driven by archaella: rotary motors attached to long extracellular filaments. The structure of these motors, and particularly how they are anchored in the absence of a peptidoglycan cell wall, is unknown. Here, we use electron cryotomography to visualize the archaellar basal body in vivo in Thermococcus kodakaraensis KOD1. Compared to the homologous bacterial type IV pilus (T4P), we observe structural similarities as well as several unique features. While the position of the cytoplasmic ATPase appears conserved, it is not braced by linkages that extend upward through the cell envelope as in the T4P, but rather by cytoplasmic components that attach it to a large conical frustum up to 500 nm in diameter at its base. In addition to anchoring the lophotrichous bundle of archaella, the conical frustum associates with chemosensory arrays and ribosome-excluding material and may function as a polar organizing center for the coccoid cells.

Highlights

Motility is a fundamental property of single-celled organisms
In addition to revealing the overall structure of the archaellar basal body in vivo, we discovered a novel cytoplasmic conical structure in T. kodakaraensis associated with archaellar motility and potentially other polar organizing activities
Due to the relatively large size of T. kodakaraensis cells, only a portion of the cell was visible in the limited field of view of our highmagnification cryotomograms

Summary

Introduction

Motility is a fundamental property of single-celled organisms. Archaella are functionally analogous to bacterial flagella, but evolutionarily homologous to the type IV pilus (T4P) and type II secretion system (T2SS) machineries of bacteria [1]. An atomic structure of the archaellum fiber. Unlike T4P fibers that only assemble and disassemble, archaella assemble and can rotate in both directions to either push or pull the cell [3, 4]. Light microscopy of Halobacterium salinarum revealed discrete steps during rotation, likely corresponding to ATP hydrolysis events by the basal body ATPase, FlaI [5]. While the bacterial T4P contains two distinct ATPases for assembly and disassembly of the pilus fiber, the single ATPase FlaI drives both assembly and rotation of the archaellum [6]. The N-terminal domain of the archaellum/T2SS/T4P superfamily

Methods

Results

Conclusion