<p> This entry describes a repeat domain that occurs from one to three times in Actinobacterial proteins, some of which have LPXTG-type sortase recognition motifs for covalent attachment to the Gram-positive cell wall. Where it occurs with duplication in an LPXTG-anchored protein, it tends to be adjacent to the substrate-binding protein of the gene trio of an ABC transporter system, where that substrate-binding protein has a single copy of this same domain. This arrangement suggests a substrate-binding relay system, with the LPXTG protein acting as a substrate receptor. </p>