Chaperone-tip adhesin complex is vital for synergistic activation of CFA/I fimbriae biogenesis.

• Main Authors: Li-Hui He, Hao Wang, Yang Liu, Mei Kang, Tao Li, Chang-Cheng Li, Ai-Ping Tong, Yi-Bo Zhu, Ying-Jie Song, Stephen J Savarino, Michael G Prouty, Di Xia, Rui Bao
• Format: Article
• Language: English
• Published: Public Library of Science (PLoS) 2020-10-01
• Series: PLoS Pathogens
• Online Access: https://doi.org/10.1371/journal.ppat.1008848

Colonization factor CFA/I defines the major adhesive fimbriae of enterotoxigenic Escherichia coli and mediates bacterial attachment to host intestinal epithelial cells. The CFA/I fimbria consists of a tip-localized minor adhesive subunit, CfaE, and thousands of copies of the major subunit CfaB polymerized into an ordered helical rod. Biosynthesis of CFA/I fimbriae requires the assistance of the periplasmic chaperone CfaA and outer membrane usher CfaC. Although the CfaE subunit is proposed to initiate the assembly of CFA/I fimbriae, how it performs this function remains elusive. Here, we report the establishment of an in vitro assay for CFA/I fimbria assembly and show that stabilized CfaA-CfaB and CfaA-CfaE binary complexes together with CfaC are sufficient to drive fimbria formation. The presence of both CfaA-CfaE and CfaC accelerates fimbria formation, while the absence of either component leads to linearized CfaB polymers in vitro. We further report the crystal structure of the stabilized CfaA-CfaE complex, revealing features unique for biogenesis of Class 5 fimbriae.