PBP3+(ftsI)

__**PBP3 (ftsL)**__

PBP3 is a class B high molecular mass (HMM) penicillin binding protein. It is a monofunctional transpeptidase and constitutes a major protein of the divisosome - the cell division protein complex.

__**Structure:**__ As a HMM PBP, PBP3 posses a cytoplasmic tail, a transmembrane anchor and two domains located on the outer surface of the cytoplasmic membrane joined by a beta-rich linker.The C-terminal penicillin binding domain of PBP3 has a transpeptidase activity, allowing it to catalyse the peptide cross-linking reaction between adjacent glycan strands.

Since it is a member of the class B HMM PBBs, the N-terminal domain of PBP3 does not possess glycosyltransferase activity. Instead, it is believed to play a role in cell morphogenesis through interactions with other proteins involved in the cell cycle (Sauvage, 2008). The N-terminal 23-aa of PBP3 localise to the cytoplasm. It is thought that this domain could be responsible for the correct folding of the protein, as well as its interactions with cell division proteins such as FtsN and FtsW (Vollmer and Bertsche, 2008).

PBP3 is a monofunctional transpeptidase, essential to cell division. This is shown by the fact that cells with a temperature sensitive PBP3 mutation can't divide at restrictive temperatures and instead grow as filaments (Vollmer and Bertsche, 2008).
 * __Function:__**