Outer membrane phospholipase (ompla); Chain C
Peptidyl-Ser-tetrahedral intermediate (with previous carboxylic-ester)
SER 106;SER 152;ARG 147(Catalytic calcium binding);ASP 184(calcium 2nd site)
ACTIVE SITE SER-164, AND PARTIAL PROTEIN SEQUENCE.
Inactivation of Escherichia coli outer-membrane phospholipase A by the affinity label hexadecanesulfonyl fluoride. Evidence for an active-site serine.
Crystallization and preliminary X-ray analysis of outer membrane phospholipase A from Escherichia coli.
Role of the cofactor calcium in the activation of outer membrane phospholipase A.
A 7.4-A projection structure of outer membrane phospholipase A from Escherichia coli by electron crystallography.
Sequence comparison of outer membrane phospholipases A: implications for structure and for the catalytic mechanism.
X-RAY CRYSTALLOGRAPHY (2.1 ANGSTROMS) OF 33-289.
Structural evidence for dimerization-regulated activation of an integral membrane phospholipase.
Unusual catalytic triad of Escherichia coli outer membrane phospholipase A.
Bacterial phospholipase A: structure and function of an integral membrane phospholipase.
Outer-membrane phospholipase A: known structure, unknown biological function.
Structural investigations of calcium binding and its role in activity and activation of outer membrane phospholipase A from Escherichia coli.
Structural investigations of the active-site mutant Asn156Ala of outer membrane phospholipase A: function of the Asn-His interaction in the catalytic triad.
Functional importance of calcium binding sites in outer membrane phospholipase A.
Substrate interferes with dimerisation of outer membrane phospholipase A.
A molecular dynamics investigation of mono and dimeric states of the outer membrane enzyme OMPLA.
Detergent organisation in crystals of monomeric outer membrane phospholipase A.
For this enzyme, calcium ion is involved both in dimerization and catalysis, together with substrate ligand, according to the literature [6], [9] & [10]. Although the calcium ion is bound to the mainchain carbonyl groups of Arg147 and Ser106 from the adjacent subunit and sidechain of Ser152, to contribute to the catalysis and dimerization, it can be bound to Asp 184 (see PDB; 1qd6 & 1fw2, literature [12]). The catalytic reaction of this enzyme proceeds as follows: (1) Calcium ion as a cofactor polarizes the target bond, carbonyl bond, thereby facilitating the nucleophilic by Ser144. (2) Asn156 contributes to the activity of His142, which is a general base, either by fixing the orientation of His142 or by neutralizing the positive charge on His142. (3) His142 acts as a general base to activate the nucleophile, Ser144. (4) Ser144 makes a nucleophilic attack on the carbonyl carbon, leading to a tetrahedral oxyanion of the transition state. (5) This transietn intermediate is stabilized by mainchain amide of Gly146 as well as water-mediated interactions with the cofactor, calcium ion. (6) The transient intermediate collapses to form the acyl-enzyme intermediate. (7) A water molecule acts as a nucleophile to attack on the acyl intermediate. According to the literature [6] & [7], the mechanism seems to be similar to that of serine proteases such as trypsin, except for the involvement of calcium ion as a cofactor.