Structural characterization of the complex between hen egg-white lysozyme and Zr$^{IV}$ -Substituted Keggin polyoxometalate as artificial protease
Abstract
Successful co-crystallization of a noncovalent complex between hen egg-white lysozyme (HEWL) and the monomeric Zr$^{IV}$-substituted Keggin polyoxometalate
(POM) (Zr1K1), (Et$_2$NH$_2$)$_3$ [Zr(PW$_{11}$O$_{39}$)] (1), has been achieved, and its single-crystal X-ray structure has been determined. The dimeric Zr$^{IV}$-substituted Keggin-type polyoxometalate (Zr1K2), (Et$_2$NH$_2$)$_{10}$[Zr(PW$_{11}$O$_{39}$)$_2$] (2), has been previously shown to exhibit remarkable selectivity towards HEWL hydrolysis. The reported X-ray structure shows that the hydrolytically active Zr$^{IV}$-substituted Keggin POM exists as a monomeric species. Prior to hydrolysis, this monomer interacts with HEWL in the vicinity of the previously identified cleavage sites found at Trp28-Val29 and Asn44-Arg45, through water-mediated H-bonding and electrostatic interactions. Three binding sites are observed at the interface of the negatively charged Keggin POM and the positively charged regions of HEWL at: 1) Gly16, Tyr20, and Arg21; 2) Asn44, Arg45, and Asn46; and 3) Arg128.