Mass spectrometry insights into interactions of selenoprotein P with auranofin and cisplatin

Abstract

The reactivity of selenoprotein P (a serum selenoprotein containing 10 selenocysteine (SeCys), 17 cysteine (Cys) and 14 histidine (His) residues) with two metallodrugs (auranofin and cisplatin) was investigated. The selenoprotein was purified from human serum by sequential affinity chromatography using immobilized metal (Co²⁺) affinity chromatography (IMAC) and heparine affinity, followed by solid-phase extraction preconcentration. The purified selenoprotein P was sequenced by nanoLC-MS/MS to reach a complete sequence coverage. It eluted from SEC as two major peaks likely to correspond to the glycosylated and non-glycosylated forms and a minor one, probably a truncated form. Size-exclusion chromatography with the selective Se (⁷⁸Se) and metal (¹⁹⁷Au or ¹⁹⁵Pt) detection by ICP MS showed the co-elution of selenoprotein P forms with Au and with Pt. SEC-ICP MS of the tryptic digest showed a considerable shift of the elution of selenium towards the lower molecular masses while preserving the co-elution of selenium and the metal at some elution times. NanoHPLC – electrospray MS/MS analysis of the post-reaction mixture demonstrated the formation of peptides with the privileged binding to Cys and His residues for cisplatin and SeCys and Cys residues for auranofin.