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Publication Abstract from PubMed

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.

Crystal structure of an actinidin-E-64 complex.,Varughese KI, Su Y, Cromwell D, Hasnain S, Xuong NH Biochemistry. 1992 Jun 9;31(22):5172-6. PMID:1606141^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.