This is the C-terminal domain found in SpaI present in Bacillus subtilis. SpaI is an immunity lipoprotein that protects the Gram-positive bacteria against their own lantibiotics, in this case subtilin. SpaI together with the ABC transporter SpaFEG protects the membrane from subtilin insertion [1].

1: The First structure of a lantibiotic immunity protein, SpaI from Bacillus subtilis, reveals a novel fold. Christ NA, Bochmann S, Gottstein D, Duchardt-Ferner E, Hellmich UA, Dusterhus S, Kotter P, Guntert P, Entian KD, Wohnert J; J Biol Chem. 2012;287:35286-35298. PMID:22904324