Identification of host-interacting domains of surface layer protein B from Levilactobacillus brevis and the evidence as glycoprotein

Surface layer proteins (Slps) can be found on the surface of some lactobacilli which involves in host-interaction and show immunomodulatory activity. Despite the capability of Slps to interact with C-type lectins on antigen presenting cells, present of sugar has not been confirmed except for Lentilactobacillus kefiri. In this study, we investigated the presence of sugar moiety in the structure of SlpB from Levilactobacillus brevis, and its involvement in interaction with DC-SIGN of dendritic cells. 4 fragments of sugar containing fragments were identified in SlpB, and the involvement of sugar in DC-SIGN interaction was confirmed by competitive assay against hexoses. The sequences of these fragments were identified based on the mass obtained from mass spectrometry, and the result has confirmed that these fragments were from carbohydrate binding motifs of SlpB. Analysing the binding affinities of these fragments with surface resonance plasmon analysis suggested that 2 fragments possess higher binding affinity compared to the remaining fragments, and the sum of binding affinities of these fragments was approximate the affinity of intact SlpB.