Penicillin-binding proteins
| Penicillin-binding protein, transpeptidase | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | PCN-bd_Tpept | ||||||||
| Pfam | PF00905 | ||||||||
| InterPro | IPR001460 | ||||||||
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| Available protein structures: | |
|---|---|
| Pfam | structures |
| PDB | RCSB PDB; PDBe; PDBj |
| PDBsum | structure summary |
| Penicillin-binding protein, dimerisation domain | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | PBP_dimer | ||||||||
| Pfam | PF03717 | ||||||||
| InterPro | IPR005311 | ||||||||
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| Available protein structures: | |
|---|---|
| Pfam | structures |
| PDB | RCSB PDB; PDBe; PDBj |
| PDBsum | structure summary |
Penicillin-binding proteins (PBPs) are a group of proteins that are characterized by their affinity for and binding of penicillin. They are a normal constituent of many bacteria; the name just reflects the way by which the protein was discovered. All β-lactam antibiotics (except for tabtoxinine-β-lactam, which inhibits glutamine synthetase) bind to PBPs, which are essential for bacterial cell wall synthesis. PBPs are members of a subgroup of enzymes called transpeptidases. Specifically, PBPs are DD-transpeptidases.
There are a large number of PBPs, usually several in each organism, and they are found as both membrane-bound and cytoplasmic proteins. For example, Spratt (1977) reports that six different PBPs are routinely detected in all strains of E. coli ranging in molecular weight from 40,000 to 91,000. The different PBPs occur in different numbers per cell and have varied affinities for penicillin (see appendix). The PBPs are usually broadly classified into high-molecular-weight (HMW) and low-molecular-weight (LMW) categories. Proteins that have evolved from PBPs occur in many higher organisms and include the mammalian LACTB protein.
PBPs are all involved in the final stages of the synthesis of peptidoglycan, which is the major component of bacterial cell walls. Bacterial cell wall synthesis is essential to growth, cell division (thus reproduction) and maintaining the cellular structure in bacteria. Inhibition of PBPs leads to irregularities in cell wall structure such as elongation, lesions, loss of selective permeability, and eventual cell death and lysis.
PBPs have been shown to catalyze a number of reactions involved in the process of synthesizing cross-linked peptidoglycan from lipid intermediates and mediating the removal of D-alanine from the precursor of peptidoglycan. Purified enzymes have been shown to catalyze the following reactions: D-alanine carboxypeptidase, peptidoglycan transpeptidase, and peptidoglycan endopeptidase. In all bacteria that have been studied, enzymes have been shown to catalyze more than one of the above reactions. The enzyme has a penicillin-insensitive transglycosylase N-terminal domain (involved in formation of linear glycan strands) and a penicillin-sensitive transpeptidase C-terminal domain (involved in cross-linking of the peptide subunits) and the serine at the active site is conserved in all members of the PBP family.
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