The high-resolution crystal structure of kexin (Kex2) in complex with a peptidyl-chloromethylketone inhibitor containing a noncognate lysine at the P (1) position provides the structural basis for the differential lysine/arginine selectivity that defines the prohormone (proprotein) convertase (PC) family . By comparison with the previous structures of Kex2 and furin, this structure of the acylated enzyme provides a basis for the observed decrease in the acylation rate with substrates containing a lysine at P (1) and the absence of an effect on the deacylation rate without involving mobility of the S (1) lid . The structure of the complex shows that a secondary subsite in the S (1) pocket is present, and that this site recognizes and binds the P (1) lysine in a more shallow fashion than arginine . This results in a displacement of the bound peptide away from the S385 nucleophile relative to substrates containing a P (1) arginine . It is concluded that this alternate binding site and resultant displacement of the scissile bond in the active site results in the observed decrease in the acylation rate . Studies of the inactivation kinetics of Kex2 by two peptidyl chloromethylketone inhibitors demonstrates that the selectivity between lysine and arginine at the P (1) position arises at the acylation step, consistent with what was observed with peptidyl substrates [Rockwell NC, Fuller RS (2001) J Biol Chem 276:38394-38399].
MeSH: Arginine, metabolism, Crystallography, X-Ray, Lysine, metabolism, Proprotein Convertases, chemistry, metabolism, Protein Binding, Protein Precursors, chemistry, metabolism, Saccharomyces cerevisiae Proteins, chemistry, metabolism