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Characterization of the conformational changes in recombinant human metallothioneins using ESI-MS and molecular modeling

Chan, Jayna, Huang, Zuyun, Watt, Ian, Kille, Peter and Stillman, Martin J. 2007. Characterization of the conformational changes in recombinant human metallothioneins using ESI-MS and molecular modeling. Canadian Journal of Chemistry 85 (10) , pp. 898-912. 10.1139/v07-111

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Abstract

Electrospray ionization mass spectrometry (ESI-MS) data and molecular modeling calculations were used to gain mechanistic, conformational, and domain-specific information from the acid-induced demetallation reactions of human metallothionein. The recombinant proteins studied were the single α- and β-rhMT-1a domains and the βα- and αβ-rhMT-1a two-domain species, based on the human metallothionein 1a sequence. Complete molecular models (MM3/MD) for all the fully metallated and demetallated species using a modified force field are reported for the first time. Basic residues that contribute to the ESI-MS charge states are identified from the molecular models. Demetallation took place under equilibrium conditions within a narrow pH range. For the two-domain proteins, these results support a demetallation mechanism involving the initial complete demetallation of one domain followed by the other for both βα-rhMT and αβ-rhMT. Based on the stability of the separate domains, the β domain is predicted to demetallate first in the two-domain rhMTs. Both the α domain and the β domain were observed to bind an excess of one Cd2+ ion. The metallated rhMT structures were shown to have very stable conformations, but only when fully metallated. Two or more conformations were observed at low pH in the ESI-MS data, which are interpreted as arising from the presence of structure, as opposed to a random coil, in the apo-rhMT. This is the first report of the existence of a structure in the two-domain metal-free apo-MT proteins. Only at extremely low pH does the structure open fully to give the highest charge distribution, which is associated with a random coil. Pre-existing structural features in the apo-MT would explain why the metallation reactions occur so rapidly.Key words: recombinant human metallothionein-1 (rhMT1), electrospray ionization mass spectrometry (ESI-MS), circular dichroism (CD), molecular mechanics/molecular dynamics (MM3/MD).

Item Type: Article
Date Type: Publication
Status: Published
Schools: Biosciences
Subjects: Q Science > Q Science (General)
Publisher: Canadian Science Publishing
ISSN: 0008-4042
Last Modified: 24 Jun 2017 10:42
URI: http://orca-mwe.cf.ac.uk/id/eprint/62647

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