This structural change may represent the action effected by the proteinase as it distorts its substrate towards the transition state for proteolytic cleavage. | The EMBO Journal , 1989 High-resolution X-ray diffraction study of the complex between endothiapepsin and an oligopeptide inhibitor: the analysis of the inhibitor binding and description of the rigid body shift in the enzyme ' 3, ', , 4, and ' 'Laboratory of Molecular Biology, Department of Crystallography, Birkbeck College, University of London, London WC1E 7HX, UK, and 2Department of Medicinal Chemistry, Pfizer Central Research, Groton, CT 06340, USA 30n leave from: Department of Biochemistry, Institute, Ljubljana, Yugoslavia 4Current address: Pont De Nemours & Co. Inc., Central Research & Development, Wilmington, DE 19880, USA Communicated by The conformation of the synthetic renin inhibitor CP-69,799, bound to the active site of the fungal aspartic proteinase endothiapepsin (EC ), has been determined by X-ray diffraction at A resolution and refined to the crystallographic R factor of 16%. CP-69,799 is an oligopeptide transition-state analogue inhibitor that contains a new dipeptide isostere at the P1- PI' position. This dipeptide isostere is a nitrogen analogue of the well-explored hydroxyethylene dipeptide isostere, wherein the tetrahedral PI' C,, atom has been replaced by trigonal nitrogen. The inhibitor binds in the extended conformation, filling S4 to S3' pockets, with hydroxyl group of the P1 residue positioned symmetrically between the two catalytic aspartates of the enzyme. Interactions between the inhibitor and the enzyme include 12 hydrogen bonds and extensive van der Waals contacts in all the pockets, except for S3'. The crystal structure reveals a bifurcated orientation of the P2 histidine side chain and an interesting relative rotation of the P3 phenyl ring to accommodate the cyclohexyl side chain at PI. The binding of the inhibitor to the enzyme, while producing no large distortions in the enzyme active site cleft,
