Understanding the adhesion mechanism of a mucin binding domain from Lactobacillus fermentum and its role in enteropathogen exclusion

Abstract Lactobacillus species possesses surface exposed Mucin Binding Protein (MucBP) which plays a role in adhesion to gastrointestinal mucin. MucBP contains one or more mucin binding domain (MBD), the functionality of which has yet not been characterized thoroughly. Here, we have characterized a 93-amino acid MBD (MBD 93 ) of MucBP (LAF_0673) from Lactobacillus fermentum . Multiple sequence alignment of L. fermentum MBD 93 exhibited ∼60% sequence homology with MBDs from other Lactobacillus species. Further, we cloned, expressed and purified MBD 93 from Escherichia coli as N -terminal histidine-tagged protein (6X His-MBD 93 ). The purified MBD 93 was able to bind to mucin and showed strong affinity towards the terminally expressed mucin glycans viz. N -acetylgalactosamine (GalNAc), N -acetylglucosamine (GlcNAc), Galactose (Gal), and Sialic acid ( N -acetylneuraminic acid; Neu5Ac). In silico experiments further confirmed the interaction between homology modeled MBD 93 to mucin glycans through hydrogen-bonding with its surface amino acid residues Ser 57 , Pro 58 , Ile 60 , Tyr 63 and Ala 65 . We also have demonstrated that MBD 93 was able to inhibit the adhesion of enteric pathogens, including E. coli , Salmonella Paratyphi A, Shigella sonnei and Proteus vulgaris to mucin. Our results suggested that L. fermentum MBD 93 is a functionally sufficient unit to act as an adhesin and to protect from invading enteric pathogens.