The structure of a 15-stranded actin-like filament from Clostridium botulinum

• Published in: Nature communications 2019-06, Vol.10 (1), p.2856-10, Article 2856
• Main Authors: Koh, Fujiet, Narita, Akihiro, Lee, Lin Jie, Tanaka, Kotaro, Tan, Yong Zi, Dandey, Venkata P., Popp, David, Robinson, Robert C.
• Format: Article
• Language: English
• Subjects: 631/535/1258/1259; 631/80/128/1276; Actin; Actin Cytoskeleton; Actins - genetics; Actins - metabolism; Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biology; Clostridium botulinum; Clostridium botulinum - metabolism; Coding; Cross-sections; Cryoelectron Microscopy; Crystal structure; Cytoskeleton; Cytoskeleton - physiology; Filaments; Fourier transforms; Gene Expression Regulation, Bacterial - physiology; Humanities and Social Sciences; Light; Microfilaments; Microscopy; Microtubules; Models, Molecular; multidisciplinary; Plasmids; Polarity; Polymerization; Protein Conformation; Protein folding; Proteins; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-10779-9

Microfilaments (actin) and microtubules represent the extremes in eukaryotic cytoskeleton cross-sectional dimensions, raising the question of whether filament architectures are limited by protein fold. Here, we report the cryoelectron microscopy structure of a complex filament formed from 15 protofilaments of an actin-like protein. This actin-like ParM is encoded on the large pCBH Clostridium botulinum plasmid. In cross-section, the ~26 nm diameter filament comprises a central helical protofilament surrounded by intermediate and outer layers of six and eight twisted protofilaments, respectively. Alternating polarity of the layers allows for similar lateral contacts between each layer. This filament design is stiffer than the actin filament, and has likely been selected for during evolution to move large cargos. The comparable sizes of microtubule and pCBH ParM filaments indicate that larger filament architectures are not limited by the protomer fold. Instead, function appears to have been the evolutionary driving force to produce broad, complex filaments. The plasmid-segregating actin-like protein ParM is encoded on the large, toxin carrying plasmid pCBH from Clostridium botulinum . Here the authors present the cryo-EM structure of the ParM filament that is formed from the association of 15 protofilaments and discuss its architecture.