Pneumococcal Pili Are Composed of Protofilaments Exposing Adhesive Clusters of Rrg A

PLoS Pathogens

Fabiola Giusti¹  Rino Rappuoli²  Vega Masignani²  Michèle A. Barocchi²  Barbara C. Baudner²  Antonello Covacci²  Ilaria Ferlenghi²  Markus Hilleringmann² 

[1]Department of Evolutionary Biology, University of Siena, Siena, Italy

[2]Research Center, Novartis Vaccines and Diagnostics s.r.l., Siena, Italy

关键词: Pili;    fimbriae;    Pneumococcus;    Bacterial pathogens;    Gram positive bacteria;    Amino acid sequence analysis;    Adhesives;    Sequence motif analysis;    Electron microscopy;   

DOI  :  10.1371/journal.ppat.1000026

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

Pili have been identified on the cell surface of Streptococcus pneumoniae, a major cause of morbidity and mortality worldwide. In contrast to Gram-negative bacteria, little is known about the structure of native pili in Gram-positive species and their role in pathogenicity. Triple immunoelectron microscopy of the elongated structure showed that purified pili contained RrgB as the major compound, followed by clustered RrgA and individual RrgC molecules on the pilus surface. The arrangement of gold particles displayed a uniform distribution of anti-RrgB antibodies along the whole pilus, forming a backbone structure. Antibodies against RrgA were found along the filament as particulate aggregates of 2–3 units, often co-localised with single RrgC subunits. Structural analysis using cryo electron microscopy and data obtained from freeze drying/metal shadowing technique showed that pili are oligomeric appendages formed by at least two protofilaments arranged in a coiled-coil, compact superstructure of various diameters. Using extracellular matrix proteins in an enzyme-linked immunosorbent assay, ancillary RrgA was identified as the major adhesin of the pilus. Combining the structural and functional data, a model emerges where the pilus RrgB backbone serves as a carrier for surface located adhesive clusters of RrgA that facilitates the interaction with the host.

【 授权许可】

CC BY