The Adhesion of Lactobacillus salivarius REN to a Human Intestinal Epithelial Cell Line Requires S layer Proteins
Lactobacillus salivarius REN, a novel probiotic isolated from Chinese centenarians, can adhere to intestinal epithelial cells and subsequently colonize the host. We show here that the surface layer protein choline binding protein A (CbpA) of L. salivarius REN was involved in adherence to the human colorectal adenocarcinoma cell line HT 29. Adhesion of a cbpA deletion mutant was significantly reduced compared with that of wild type, suggesting that CbpA acts as an adhesin that mediates the interaction between the bacterium and its host. To identify the molecular mechanism of adhesion, we determined the crystal structure of a truncated form of CbpA that is likely involved in binding to its cell surface receptor. The crystal structure identified CbpA as a peptidase of the M23 family whose members harbor a zinc dependent catalytic site. Therefore, we propose that CbpA acts as a multifunctional surface protein that cleaves the host extracellular matrix and participates in adherence. Moreover, we identified enolase as the CbpA receptor on the surface of HT 29 cells. The present study reveals a new class of surface layer proteins as well as the molecular mechanism that may contribute to the ability of L. salivarius REN to colonize the human gut.
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