Influence of two substrate analogues on thermodynamic properties of medium-chain acyl-CoA dehydrogenase

The objective of this work was to identify the key structural functionalities of substrate or product that modulate the thermodynamic properties of medium-chain acyl-CoA dehydrogenase (MCAD). In order to achieve this, two classes of substrate analogues, acetyl-CoA and thioether-CoAs, were complexed with MCAD and their effects on the redox properties of MCAD were measured. A pH dependence study of the redox potential of uncomplexed MCAD allowed us to compare redox properties between complexed and uncomplexed MCAD and to calculate the dissociation constants of the analogues to the three redox states of MCAD. The results from this work indicate that these analogues are not influencing the thermodynamic behavior of MCAD in the same way as natural substrate. Thus, we propose that the following two key structural features of the binding ligand are necessary for mimicking the thermodynamic effects natural substrate has on MCAD: a thioester carbonyl on carbon 1 and a fatty acyl-CoA chain length around 8 carbon units. Furthermore, with the advent of structural knowledge, insights into the interactions of these structural features with MCAD and their influence on MCAD's highly regulated dehydrogenation mechanism are discussed.