This domain is found in bacterial cell surface proteins that interact with mucins. The archetypal member of this family is the Mub-R5 B1 domain [1]. This domain has a beta-grasp fold [1].

1: Crystal structure of a mucus-binding protein repeat reveals an unexpected functional immunoglobulin binding activity. MacKenzie DA, Tailford LE, Hemmings AM, Juge N; J Biol Chem. 2009;284:32444-32453. PMID:19758995