title: Selective hydrolysis of oxidized insulin chain B by a Zr(IV)-substituted Wells-Dawson polyoxometalate.
abstract: We report for the first time on the selective hydrolysis of a polypeptide system by a metal-substituted polyoxometalate (POM). Oxidized insulin chain B, a 30 amino acid polypeptide, was selectively cleaved by the Zr(IV)-substituted Wells-Dawson POM, K15H[Zr(α2-P2W17O61)2]·25H2O, under physiological pH and temperature conditions in aqueous solution. HPLC-ESI-MS, LC-MS/MS, MALDI-TOF and MALDI-TOF MS/MS data indicate hydrolysis at the Phe1-Val2, Gln4-His5, Leu6-Cys(SO3H)7, and Gly8-Ser9 peptide bonds. The rate of oxidized insulin chain B hydrolysis (0.45 h(-1) at pH 7.0 and 60 °C) was calculated by fitting the integration values of its HPLC-UV signal to a first-order exponential decay function. (1)H NMR measurements show significant line broadening and shifting of the polypeptide resonances upon addition of the Zr(IV)-POM, indicating that interaction between the Zr(IV)-POM and the polypeptide takes place in solution. Circular dichroism (CD) measurements clearly prove that the flexible unfolded nature of the polypeptide was retained in the presence of the Zr(IV)-POM. The thermal stability of the Zr(IV)-POM in the presence of the polypeptide chain during the hydrolytic reaction was confirmed by (31)P NMR spectroscopy. Despite the highly negative charge of the Zr(IV)-POM, the mechanism of interaction appears to be dominated by a strong metal-directed binding between the positively charged Zr(IV) center and negatively charged amino acid side chains.
authors.affiliation: KU Leuven, Department of Chemistry, Celestijnenlaan 200F, B-3001 Heverlee, Belgium. tatjana.vogt@chem.kuleuven.be.
authors.forename: Annelies
authors.initials: A
authors.lastname: Sap
authors.forename: Gregory
authors.initials: G
authors.lastname: Absillis
authors.forename: Tatjana N
authors.initials: TN
authors.lastname: Parac-Vogt
mesh_terms: D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D006868:Hydrolysis; D007328:Insulin / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry / Q000379:methods; D010084:Oxidation-Reduction; D017973:Tungsten Compounds / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*; D000099294:Polyoxometalates
chemical_list: D007328:Insulin; D017973:Tungsten Compounds; D015040:Zirconium; C102296:polyoxometalate I; D000099294:Polyoxometalates