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Third calcium ion found in an inhibitor-bound phospholipase A2.

Acta crystallographica. Section D, Biological crystallography (2006-03-23)
K Sekar, D Gayathri, D Velmurugan, J Jeyakanthan, T Yamane, M J Poi, M D Tsai
ABSTRACT

The lipolytic enzyme phospholipase A2 plays a crucial role in lipid metabolism and catalyzes hydrolysis of the fatty-acid ester bond at the sn-2 position of phospholipids. Here, the crystal structure (1.7 A resolution) of the triple mutant (K53,56,121M) of bovine pancreatic phospholipase A2 complexed with an organic molecule, p-methoxybenzoic acid (anisic acid), is reported. Residues 60-70 (the surface-loop residues) are ordered and adopt conformations which are different from those normally found in structures in which a second calcium ion is present. It is interesting to note that for the first time a third calcium ion has been identified. In addition, four Tris (2-amino-2-hydroxymethyl-1,3-propanediol) molecules were located. It is believed that one of the Tris molecules plays a role in clamping the third calcium ion and that another is involved in controlling the dynamics of the surface loop through hydrogen bonds.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
p-Anisic acid, ≥99%, FG
Supelco
Melting point standard 182-184°C, analytical standard
Sigma-Aldrich
4-Methoxybenzoic acid, ReagentPlus®, 99%
Sigma-Aldrich
Phospholipase A2 from bovine pancreas, lyophilized powder, ≥20 units/mg protein