Binding of fatty acids to beta-cryptogein: quantitative structure-activity relationships and design of selective protein mutants.

Binding of fatty acids to cryptogein, the proteinaceous elicitor from Phytophthora, was studied by using molecular docking and quantitative structure-activity relationships analysis. Fatty acids bind to the groove located inside the cavity of cryptogein. The structure-activity model was constructed for the set of 27 different saturated and unsaturated fatty acids explaining 87% (81% cross-validated) of the quantitative variance in their binding affinity. The difference in binding between saturated and unsaturated fatty acids was described in the model by three electronic descriptors: the energy of the lowest unoccupied molecular orbital, the energy of the highest occupied molecular orbital, and the heat of formation. The presence of double bonds in the ligand generally resulted in stronger binding. The difference in binding within the group of saturated fatty acids was explained by two steric descriptors, i.e., ellipsoidal volume and inertia moment of length, and one hydrophobicity descriptor, i.e., lipophility. The developed model predicted strong binding for two biologically important molecules, geranylgeranyol and farnesol playing an important role in plant signaling as lipid anchors of some membrane proteins. Elicitin mutants selectively binding only one type of ligand were designed for future experimental studies.