An intersubunit lock-and-key 'Clasp' motif in the dimer interface of Delta class glutathione transferase

摘要

Structural investigations of a GST (glutathione transferase), adGSTD4-4, from the malaria vector Anopheles dirus show a novel lock-and-key 'Clasp' motif in the chiller interface of file Delta class enzyme. This motif also appears to be highly conserved across several insect GST classes, but differs from a previously reported mammalian lock-and-key motif. The aromatic 'key' residue not Only inserts into a hydrophobic pocket, the 'lock', of the neighouring subunit, but also acts as, part of the 'lock' for the other subunit 'key'. The 'key' residues from both subunits show aromatic ring stacking with each other in a pi-pi interaction, generating a 'Clasp' in file middle of the Still interface. Enzyme catalytic and structural characterizations revealed that single amino acid replacements in this 'Clasp' motif impacted oil catalytic efficiencies, substrate selectivity and stability. Substitutions to file 'key' residue create strong positive co-operativity for glutathione binding, with a Hill coefficient approaching 2. The lock-and-key motif in general and especially the 'Clasp' motif with the pi-pi interaction appear to play a pivotal role in Subunit communication between active sites, as well as in stabilizing the quaternary structure. Evidence of allosteric effects suggests all important role for this particular inter-subunit architecture in regulating catalytic activity through conformational transitions Of Subunits. The observation of cooperativity in the mutants also implies that glutathione ligand binding and dimerization are linked. Quaternary structural changes of all Mutants suggest that Subunit assembly or dimerization basically manipulates subunit communication.