Direct characterisation by electrospray ionisation mass spectroscopy of mercuro-polypeptide complexes after deprotection of acetamidomethyl groups from protected cysteine residues of synthetic polypeptides

In this paper, we describe a rapid procedure to characterise the products g enerated in the presence of mercuric salts following removal of the acetami domethyl (Acm)-protecting group from cysteine residues of synthetic polypep tides prepared by solid-phase peptide synthesis (SPPS) methods. In particul ar, electrospray ionisation mass spectrometry (ESI-MS) procedures have been employed to characterise the mercuro-polypeptide products related to the r ibosomal L36 protein isolated from the bacterium Thermus thermophilus. The results demonstrate that very stable mercuro-polypeptide complexes can form under standard conditions of deprotection involving Hg2+ salts in the pres ence of a reductant such as P-mercaptoethanol. Metal ion exchange effects i nvolving other divalent metal ions, such as Co2+ Or Zn2+ , can also be moni tored by similar procedures, thus permitting the relative affinity and sele ctivity for metal ion-polypeptide interactions to be qualitatively assessed . Since the Thermus thermophilus ribosomal L36 protein contains a putative zinc finger binding CCCH motif, these procedures enable the formation of me tal-ion complexes of synthetic polypeptides related to this structural moti f to be directly examined. (C) 2000 Elsevier Science B.V. All rights reserv ed.