Differential profiles of gastrointestinal proteins interacting with peptidoglycans from Lactobacillus plantarum and Staphylococcus aureus.

Peptidoglycan (PGN) is a major cell wall component of Gram-positive bacteria that contributes to the regulation of host immunity in the gastrointestinal tract (GIT). Although Gram-positive bacteria contain structurally distinct PGNs that are considered to differently interact with the GIT, PGN-binding proteins (PGN-BPs) in the GIT have been poorly understood. In the present study, we purified PGNs from Lactobacillus plantarum and Staphylococcus aureus (named as Lp.PGN and Sa.PGN, respectively) and identified Lp.PGN-BPs and Sa.PGN-BPs in the lysate of mouse GIT. Lp.PGN activated nucleotide-binding oligomerization domain (NOD) 1 and NOD2, whereas Sa.PGN activated NOD2, but not NOD1, implying that both PGNs retained the biological activity and were differently recognized by the host cells. PGN-BPs were isolated by precipitation with Lp.PGN or Sa.PGN and identified using LTQ-Orbitrap hybrid Fourier transform mass spectrometry. Three independent experiments demonstrated that 18 Lp.PGN-BPs and 6 Sa.PGN-BPs were reproducibly obtained with statistical significance (P<0.05). Both Lp.PGN and Sa.PGN bound to proteins which are related to cytoskeleton, microbial adhesion, and mucosal integrity. Lp.PGN selectively bound to proteins related to gene expression, chaperone, and antimicrobial function. However, Sa.PGN preferentially interacted with proteins involved in adherence and invasion of pathogens. Collectively, these results suggest that bacterial PGNs interact with the proteins regulating mucosal homeostasis and immunity in the gut and PGNs of commensals and pathogens might be also differentially recognized in the GIT.