title: Crystal structure of an actinidin-E-64 complex.
abstract: E-64, 1-(L-trans-epoxysuccinylleucylamino)-4-guanidinobutane, is a potent and highly selective irreversible inhibitor of cysteine proteases. The crystal structure of a complex of actinidin and E-64 has been determined at 1.86-A resolution by using the difference Fourier method and refined to an R-factor of 14.5%. The electron density map clearly shows that the C2 atom of the E-64 epoxide ring is covalently bonded to the S atom of the active-site cysteine 25. The charged carboxyl group of E-64 forms four H-bonds with the protein and thus may play an important role in favorably positioning the inhibitor molecule for nucleophilic attack by the active-site thiolate anion. The interaction features between E-64 and actinidin are very similar to those seen in the papain-E-64 complex; however, the amino-4-guanidinobutane group orients differently. The crystals of the actinidin-E-64 complex diffracted much better than the papain-E-64 complex, and consequently the present study provides more precise geometrical information on the binding of the inhibitor. Moreover, this study provides yet another confirmation that the binding of E-64 is at the S subsites and not at the S' subsites as has been previously proposed. The original actinidin structure has been revised using the new cDNA sequence information.
authors.affiliation: Department of Biology, University of California, San Diego, La Jolla 92093-0317.
authors.forename: K I
authors.initials: KI
authors.lastname: Varughese
authors.forename: Y
authors.initials: Y
authors.lastname: Su
authors.forename: D
authors.initials: D
authors.lastname: Cromwell
authors.forename: S
authors.initials: S
authors.lastname: Hasnain
authors.forename: N H
authors.initials: NH
authors.lastname: Xuong
mesh_terms: D001665:Binding Sites; D003546:Cysteine Endopeptidases / Q000737:chemistry* / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000737:chemistry*; D004583:Electrons; D007930:Leucine / Q000031:analogs & derivatives* / Q000737:chemistry; D008968:Molecular Conformation; D014961:X-Ray Diffraction
chemical_list: D015853:Cysteine Proteinase Inhibitors; D003546:Cysteine Endopeptidases; C018745:actinidain; D007930:Leucine; C024974:E 64