Abstract
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.
Highlights
The Gram-positive bacterium Streptococcus pneumoniae, known as pneumococcus, is one of the most important human pathogens causing respiratory tract infections such as sinusitis, otitis media, and community acquired pneumonia, and invasive diseases such as septicemia and meningitis
To date structural information of the native pilus in Gram-positive bacteria is lacking, the elucidation of their structure and function are of great interest
Our approach consisted in obtaining native purified pili from a pathogenic strain of Streptococcus pneumoniae to study pilus structure and function
Summary
The Gram-positive bacterium Streptococcus pneumoniae, known as pneumococcus, is one of the most important human pathogens causing respiratory tract infections such as sinusitis, otitis media, and community acquired pneumonia, and invasive diseases such as septicemia and meningitis. A major virulence factor of Streptococcus pneumoniae is the polysaccharide capsule, by which pneumococci are grouped into at least ninety different serotypes [5]. Other genetic factors, such as CbpA (choline-binding protein A) and pneumolysin, have been described to be of importance for virulence [6,7,8]. Similar pili-like surface structures had been identified in other Gram-positive bacteria, such as Corynebacterium diphtheriae [13,14], Actinomyces spp. [15], group A streptococci (GAS) [16], group B streptococci (GBS) [17] and recently Mycobacterium tuberculosis [18] where they were shown to play an important role in the interaction with the host at different stages of infection
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
