Conners, R. | bioRxiv Science

bioRxiv2021

New insights into the architecture and dynamics of archaella

Archaea swim by means of a unique molecular machine called the archaellum. The archaellum consists of an ATP-powered intracellular motor that drives the rotation of an extracellular filament, allowing the cell to rapidly propel itself through liquid media. The archaellum filament comprises multiple copies of helically organised subunits named archaellins. While in many species several archaellin homologs are encoded in the same operon, structural studies conducted to date have suggested that archaella consist of only one protein species. Thus, the role of the remaining archaellin genes remains elusive. Here we present the structure of the Methanocaldococcus villosus archaellum filament at 3.08 [A] resolution. We find that the filament is composed of two alternating archaellins - ArlB1 and ArlB2, suggesting that the architecture and assembly of archaella is more complex than previously thought. Moreover, we identify two major structural elements that enable the archaellum filament to move. Our findings provide new insights into archaeal motility and challenge the current view on the archaellum architecture and assembly.

microbiology↗

bioRxiv2021

CryoEM structure of the outer membrane secretin channel pIV from the f1 filamentous bacteriophage

The Ff family of filamentous bacteriophages infect gram-negative bacteria, but do not cause lysis of their host cell. Instead, new virions are extruded via the phage-encoded pIV protein, which has homology with bacterial secretins. Here, we determine the structure of pIV from the f1 filamentous bacteriophage at 2.7 [A] resolution by cryo-electron microscopy, the first near-atomic structure of a phage secretin. Fifteen f1 pIV subunits assemble to form a gated channel in the bacterial outer membrane, with associated soluble domains projecting into the periplasm. We model channel opening and propose a mechanism for phage egress. By single-cell microfluidics experiments, we demonstrate the potential for secretins such as pIV to be used as adjuvants to increase the uptake and efficacy of antibiotics in bacteria. Finally, we compare the f1 pIV structure to its homologues to reveal similarities and differences between phage and bacterial secretins.

biophysics↗