This domain is found in the N-terminal region of the receptor-binding protein of bacteriophage TP901-1, which infects Lactococcus lactis. The receptor-binding protein of phage TP901-1 is termed the lower baseplate protein (BppL) and is trimeric in nature. The N-terminal domain of BppL plugs into the upper baseplate protein (BppU) [1].

1: Structure and molecular assignment of lactococcal phage TP901-1 baseplate. Bebeacua C, Bron P, Lai L, Vegge CS, Brondsted L, Spinelli S, Campanacci V, Veesler D, van Heel M, Cambillau C; J Biol Chem. 2010;285:39079-39086. PMID:20937834