Exploring Subunit Communication of Malate Dehydrogenase through Interface Point‐ Mutations

Abstract

Malate Dehydrogenase (MDH) catalyzes the oxidation/reduction of malate/oxaloacetate through coupling with NAD+/NADH conversion, a key area in cellular metabolism and has been shown to be regulated by citrate. MDH is a homo‐dimer and x‐ray structures show a flexible loop, which upon substrate or citrate binding induces a closed conformational in one subunit, while the other remains open. This implies an as of yet unknown means of communication between the two subunits to convey the open/closed loop response. Concurrent work in the Bell Lab has shown two mutations, S266A & L269A, located in the active site and interface regions display significant changes in kinetic parameters. To further probe these regions and assess individual residue contributions to subunit communication several additional point mutants (I88A, K261M/Q, S270A/C, T255E/V) located between the active site and the subunit interface have been constructed, expressed, purified and characterized. The I88A mutant protein has a 10,000 fold decrease in Vmax while that of the T255E mutant is decreased 1,000 fold. Km for NADH is significantly increased in the I88A mutant while that for T255E remains unchanged. This suggests that decreased affinity for NADH in the I88A mutant results from disruption of the subunit interface., I88 is thought to interact with L269 on the opposite chain, while T255 may be involved in oxaloacetate/malate/citrate binding at the active site. This data is consistent with predicted effects of interface and active site mutations and contributes to a detailed understanding of a predicted inter‐subunit relay system to induce asymmetric conformational changes and ligand binding in this homo‐dimeric enzyme.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.