The LCP family or TagU family of proteins is a conserved
gram-positive cell wall or cell membrane. It was initially thought as the LytR (lytic repressor) component of a LytABC operon encoding autolysins,[1] but the mechanism of regulation was later realized to be the production of TA molecules. It was accordingly renamed TagU.[2]
The "LCP" acronym derives from three proteins initially identified to contain this domain, LytR (now TagU, Q02115), cpsA ("Capsular polysaccharide expression regulator"), and psr ("PBP 5 synthesis repressor"). These proteins were mistaken as transcriptional regulators via different reasons, but all three of them are now known to be TagU-like enzymes.[3][4] While TagU itself only attaches TA molecules to the peptidoglycan cell wall (forming WTA), other LCP proteins may glycosylate cell wall proteins (A. oris LcpA, PDB: 5V8C)[5] or attach TA molecules to a cell membrane anchor (forming LTA).[6] Most, if not all, LCP proteins also have a secondary pyrophosphatase activity.[7]
Typical TagU proteins are made up of an N-terminal transmembrane domain (for anchoring), an optional, non-conserved accessory domain (CATH 3tflA01), a core catalytic domain, and sometimes a C-terminal domain for which the structure is unknown. The core LCP domain is a magnesium-dependent enzyme.[2]
