MOLECULAR MODELING OF THE STRUCTURES OF HUMAN AND RAT PANCREATIC CHOLESTEROL ESTERASES

Structural models have been generated for rat and human cholesterol es terases by molecular modeling. For rat cholesterol esterase, three sep arate models were generated according to the following procedure: (1) the cholesterol esterase sequence was aligned with those of three temp late enzymes: Torpedo californica acetylcholinesterase, Geotrichum can didum lipase and Candida rugosa lipase; (2) the X-ray structure coordi nates of the three template enzymes were used to construct cholesterol esterase models by amino acid replacements of matched sequence positi ons and by making sequence insertions and deletions as required; (3) b ad contacts in each of the cholesterol esterase models were relaxed by molecular dynamics and mechanics; (4) the three cholesterol esterase models were merged into one by arithmetic averaging of atomic coordina tes; (5) Ramachandran analysis indicated that the model generated from the AChE template possessed the best set of phi/psi angles. Therefore , this model was subjected to molecular dynamics, with harmonic constr aints imposed on the C-alpha coordinates to drive them toward the coor dinates of the averaged model. (6) Subsequent relaxation by molecular mechanics produced the final rat cholesterol esterase model. A model f or human cholesterol esterase was produced by repeating steps 1-3 abov e, albeit with the rat cholesterol esterase model as the template. Hyd rophobic and electrostatic analyses of the rat and human cholesterol e sterase models suggest the structural origins of molecular recognition of hydrophobic substrates and interfaces, of charged interfaces, and of bile salt activators.