Figure 4.

Proposed catalytic mechanism for sPLA2. Asp98 and His47 constitute the catalytic dyad which plays a key role in catalysis. These two residues are hydrogen-bonded together and further connected with the Ca²⁺ ion with the help of two water molecules (w5 and w6). His47 facilitates the deprotonation of w5 water molecule, subsequently attacks the sn-2 carbonyl group of the substrate and forms the tetrahedral intermediate. The rate-limiting step is the decomposition of the tetrahedral intermediate [20].