Pneumococcal pili are composed of protofilaments exposing adhesive clusters of Rrg A.
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.
Hilleringmann
Markus
M
Research Center, Novartis Vaccines and Diagnostics s.r.l., Siena, Italy. markus.hilleringmann@novartis.com
Giusti
Fabiola
F
Baudner
Barbara C
BC
Masignani
Vega
V
Covacci
Antonello
A
Rappuoli
Rino
R
Barocchi
Michèle A
MA
Ferlenghi
Ilaria
I
D018829:Adhesins, Bacterial / Q000737:chemistry / Q000378:metabolism*; D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000737:chemistry / Q000378:metabolism; D036781:Fimbriae Proteins / Q000737:chemistry / Q000378:metabolism*; D010861:Fimbriae, Bacterial / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D011485:Protein Binding; D013296:Streptococcus pneumoniae / Q000378:metabolism / Q000648:ultrastructure*; D015534:Trans-Activators / Q000378:metabolism*
D018829:Adhesins, Bacterial; D001426:Bacterial Proteins; D016326:Extracellular Matrix Proteins; D015534:Trans-Activators; C470697:rlrA protein, Streptococcus pneumoniae; D036781:Fimbriae Proteins