Poster: Lipids & related molecules

Abs # 313: Molecular modeling of CYP74 enzymes and enzyme substrate complex

Presenter:	Raman, Girija , graman@ucdavis.edu
Authors	Raman, Girija  (A)   Chehab, E.Wassim  (A)   Gopalan, Banu  (A) (B)  Dehesh, Katayoon  (A)
Affiliations:	(A): UC Davis (B): Pacific Northwest National Laboratory

Plants have developed a multitude of defense mechanisms against adverse biotic and abiotic stress signals. One of the major signaling pathways induced by stress and developmental processes is the lipoxygenase pathway that converts linoleic and α-linolenic acids into a wide range of oxylipins. Oxylipins, the metabolites derived from lipid peroxidation, play a pivotal role in an array of biological functions, ranging from responses to pathogens and wounding, to production of compounds for the flavor industry. The enzyme substrate specificity and/or preference contribute to the oxylipin signature as the determinant of plant response to environmental stimuli. To examine the underlying structural basis for enzyme substrate specificity, we have modeled a number of allene oxide synthases (AOS) and hydroperoxide lyases (HPL) from different plant species together with their respective substrates. The models of various substrates docked into the proposed binding site of the enzymes revealed the critical residues and their binding free energy with various substrates as a determinant of structure-function relationship.The refinement of these models involved the minimization of the whole structure in the presence of water using harmonic potential and the steepest descent gradient method to less than 1 kcal mol^-1 Å ^-1 These studies led to identification of a number of critical residues involved in substrate binding of these enzymes. Furthermore, simultaneous substitutions of the bulky and small amino acid residues in the binding pocket are performed to potentially reveal the functional interplay of the sequence determinants for catalytic activity. These data are experimentally validated by in vitro assays.