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Publication Abstract from PubMed

BibA, a group B streptococcus (GBS) surface protein, has been shown to protect the pathogen from phagocytic killing by sequestering a complement inhibitor: C4b-binding protein (C4BP). Here, the X-ray crystallographic structure of a GBS BibA fragment (BibA126-398) and a low-resolution small-angle X-ray scattering (SAXS) structure of the full-length N-terminal domain (BibA34-400) are described. The BibA126-398 fragment crystal structure displayed a novel and predominantly helical structure. The tertiary arrangement of helices forms four antiparallel three-helix-bundle-motif repeats, with one long helix from a bundle extending into the next. Multiple mutations on recombinant BibA34-400 delayed the degradation of the protein, and circular dichroism spectroscopy of BibA34-400 suggested a similar secondary-structure composition to that observed in the crystallized BibA126-398 fragment. A model was generated for the 92 N-terminal residues (BibA34-125) using structural similarity prediction programs, and a BibA34-400 model was generated by combining the coordinates of BibA34-126 and BibA126-398. The X-ray structure of BibA126-398 and the model of BibA34-400 fitted well into the calculated SAXS envelope. One possible binding site for the BibA N-terminal domain was localized to the N-terminal CCP (complement-control protein) domains of the C4BP alpha-chain, as indicated by the decreased binding of BibA to a DeltaCCP1 C4BP alpha-chain mutant. In summary, it is suggested that the GBS surface protein BibA, which consists of three antiparallel alpha-helical-bundle motifs, is unique and belongs to a new class of Gram-positive surface adhesins.

Novel structure of the N-terminal helical domain of BibA, a group B streptococcus immunogenic bacterial adhesin.,Manne K, Chattopadhyay D, Agarwal V, Blom AM, Khare B, Chakravarthy S, Chang C, Ton-That H, Narayana SVL Acta Crystallogr D Struct Biol. 2020 Aug 1;76(Pt 8):759-770. doi:, 10.1107/S2059798320008116. Epub 2020 Jul 27. PMID:32744258^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.