Study On The Molecular Mechanism Of The Inhibition Of DHCR24 Inhibitor And Gene Point Pathogenic Mutations Using Molecular Simulation Method

3β-hydroxysterol-△24-reductase (DHCR24) is an enzyme of the final step of cholesterol synthesis in human, catalyzing cholesterol synthesis from desmosterol, and also has an anti-apoptotic function. U18666a is reported to be a non-competitive inhibitor on blockingthe activity of DHCR24, but the detail mechanism remains elusive. In humans, DHCR24 missense mutations(Y471S,N294T, K306N, E191K) resulted in desmosterolosis, characterized as multiple congenital anomalies and developmental anomalies, but there is no report about how mutations affect the DHCR24 activity.Our study explored the mechanism of the inhibitory effect of U 18666a on DHCR24 activity using molecular simulation method. The effect of one-point mutation Y471S, N294T, K306N, E191K and two-point mutation N294T/K306N of DHCR24 on the structure of DHCR24 was also studied using methods of mutation and molecular simulation.In the study of interactions between U18666a and DHCR24, homology modeling, molecular docking and molecular dynamics simulation method are performed, the resultsshowed that the binding affinity of substrate desmosterol (des) to DHCR24 had to be changed in response to the U18666A, compared with the complex without U18666a. Analysis of secondary structure changes showed that U18666a binds to DHCR24resulted in the significant structural change of DHCR24, which might affect the interactions of DHCR24, FAD, and desmosterol. Our study suggested that U 18666a increases the affinity of substrates desmosterol on the DHCR24, which may inhibit the dissociation of substrate/product from the enzyme after the completion of the reaction thus inhibiting the enzyme catalysis. This conclusion is consistent with the non-competitive inhibition of U18666a to DHCR24 observed in a previous study of enzyme activity assay.In study of the effects of the mutations of DHCR24 on its structures, calculation results of free binding energy showed that the binding ability of substrate desmosterol to the DHCR24 complex has a tendency of increase in all of these five mutations, compared with the wild type DHCR24-fad-des,. Analysis of secondary structure changes showed that N294T/K306N mutation has the most significant changes of secondary structure, and also has the greatest degree influence on the binding activity of the enzyme and the substrate, which is consistent with that N294T/K306N mutation inhibits DHCR24 enzyme activity and caused the most serious cholesteryl acidemia of desmosterolosis in the early report.