This is the second domain on the N-terminal region found on the alpha C protein (ACP). ACP is found in Streptococcus and acts as an invasin which plays a role in the internalisation and translocation of the organism across human epithelial surfaces [1]. Group B Streptococcus is the leading cause of diseases including bacterial pneumonia, sepsis and meningitis. ACP consists of an N-terminal domain (NtACP; 170 amino acids) followed by a variable number of tandem repeats (82 amino acids each) and a C-terminal domain (45 amino acids) containing an LPXTG peptidoglycan-anchoring motif. The NtACP, contains two structural domains, D1 and D2. D1, the more distal (amino-terminal) portion Pfam:PF08829 and consists of a beta sandwich with strong structural homology to fibronectin's integrin-binding region (FnIII10). This entry, D2 (connects distally to Domain 1 and proximally to the repeat region) [1] consists of three antiparallel alpha helix coils [2]. It is suggested that the GAG-binding region of ACP may extend from Domain 2 into the repeat region [3].

1: Crystal structure of the N-terminal domain of the group B streptococcus alpha C protein. Auperin TC, Bolduc GR, Baron MJ, Heroux A, Filman DJ, Madoff LC, Hogle JM; J Biol Chem. 2005;280:18245-18252. PMID:15753100

2: The group B streptococcal alpha C protein binds alpha1beta1-integrin through a novel KTD motif that promotes internalization of GBS within human epithelial cells. Bolduc GR, Madoff LC; Microbiology. 2007;153:4039-4049. PMID:18048918

3: Identification of a glycosaminoglycan binding region of the alpha C protein that mediates entry of group B Streptococci into host cells. Baron MJ, Filman DJ, Prophete GA, Hogle JM, Madoff LC; J Biol Chem. 2007;282:10526-10536. PMID:17259175