Structural and Molecular Biology of a Protein-Polymerizing Nanomachine for Pilus Biogenesis

•This article reviews progress on pilus biogenesis by the chaperone-usher pathway•Details of the subunit incorporation cycle by the usher are discussed and knowledge gaps identified•General principles of polymer assembly by nanomachines are established by comparing the mechanism of the usher with that of DNA polymerases

Bacteria produce protein polymers on their surface called pili or fimbriae that serve either as attachment devices or as conduits for secreted substrates. This review will focus on the chaperone-usher pathway of pilus biogenesis, a widespread assembly line for pilus production at the surface of Gram-negative bacteria and the archetypical protein-polymerizing nanomachine. Comparison with other nanomachines polymerizing other types of biological units, such as nucleotides during DNA replication, provides some unifying principles as to how multidomain proteins assemble biological polymers.

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