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The group B streptococcal alpha C protein binds ₁β₁-integrin through a novel KTD motif that promotes internalization of GBS within human epithelial cells

Gilles R. Bolduc^1,2,

¹ Channing Laboratory, 181 Longwood Avenue, Boston, MA 02115, USA
² Department of Medicine, Brigham and Women's Hospital, 75 Fransis Street, Boston, MA 02115, USA

Correspondence
Gilles R. Bolduc
grbolduc{at}comcast.net

Group B Streptococcus (GBS) is the leading cause of bacterial pneumonia, sepsis and meningitis among neonates and a cause of morbidity among pregnant women and immunocompromised adults. GBS epithelial cell invasion is associated with expression of alpha C protein (ACP). Loss of ACP expression results in a decrease in GBS internalization and translocation across human cervical epithelial cells (ME180). Soluble ACP and its 170 amino acid N-terminal region (NtACP), but not the repeat protein RR', bind to ME180 cells and reduce internalization of wild-type GBS to levels obtained with an ACP-deficient isogenic mutant. In the current study, ACP colocalized with ₁β₁-integrin, resulting in integrin clustering as determined by laser scanning confocal microscopy. NtACP contains two structural domains, D1 and D2. D1 is structurally similar to fibronectin's integrin-binding region (FnIII10). D1's (KT)D146 motif is structurally similar to the FnIII10 (RG)D1495 integrin-binding motif, suggesting that ACP binds ₁β₁-integrin via the D1 domain. The (KT)D146A mutation within soluble NtACP reduced its ability to bind ₁β₁-integrin and inhibit GBS internalization within ME180 cells. Thus ACP binding to human epithelial cell integrins appears to contribute to GBS internalization within epithelial cells.

Present address: Cequent Pharmaceuticals, Inc., One Kendall Square, Building 700, Cambridge, MA 02139, USA.