Abstract
Group B Streptococcus (GBS) is a major cause of invasive disease in infants. Like other Gram-positive bacteria, GBS uses a sortase C-catalyzed transpeptidation mechanism to generate cell surface pili from backbone and ancillary pilin precursor substrates. The three pilus types identified in GBS contain structural subunits that are highly immunogenic and are promising candidates for the development of a broadly-protective vaccine. Here we report the X-ray crystal structure of the backbone protein of pilus 2b (BP-2b) at 1.06Å resolution. The structure reveals a classical IgG-like fold typical of the pilin subunits of other Gram-positive bacteria. The crystallized portion of the protein (residues 185-468) encompasses domains D2 and D3 that together confer high stability to the protein due to the presence of an internal isopeptide bond within each domain. The D2+D3 region, lacking the N-terminal D1 domain, was as potent as the entire protein in conferring protection against GBS challenge in a well-established mouse model. By site-directed mutagenesis and complementation studies in GBS knock-out strains we identified the residues and motives essential for assembly of the BP-2b monomers into high-molecular weight complexes, thus providing new insights into pilus 2b polymerization.
Highlights
Streptococcus agalactiae is an opportunistic Gram-positive pathogen causing early and late onset neonatal invasive diseases including sepsis, pneumonia, and meningitis, as well as severe infections in the elderly and in immune-compromised patients [1, 2]
Analytical size-exclusion chromatography (SEC) revealed that the backbone protein of pilus 2b (BP-2b) fragment is monomeric in solution, the theoretical molecular weight is 32kDa, compatible with the apparent molecular weight calculated by SEC, where the BP-2b185468 protein fragment eluted as a single peak after Ovalbumin (44 kDa) and prior to Myoglobin (17 kDa) MW standards
In this work we report the structural and biochemical characterization of the backbone protein of Group B Streptococcus (GBS) pilus 2b (BP-2b) that is one out of three pilus types identified in GBS by genome analysis [7, 55]
Summary
Streptococcus agalactiae ( known as Group B Streptococcus or GBS) is an opportunistic Gram-positive pathogen causing early and late onset neonatal invasive diseases including sepsis, pneumonia, and meningitis, as well as severe infections in the elderly and in immune-compromised patients [1, 2]. GBS expresses three structurally distinct pilus types, each containing at least two antigens capable of eliciting protective immunity. Crystal Structure of GBS Pilus 2b Backbone Protein will not benefit from it There are no products in development or marketed products to declare. This does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials, as detailed online in the guide for authors
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