2j4f

From Proteopedia

Revision as of 10:42, 8 November 2007

TORPEDO ACETYLCHOLINESTERASE- HG HEAVY-ATOM DERIVATIVE

Overview

Chemical modification of Torpedo californica acetylcholinesterase by, various sulfhydryl reagents results in its conversion to one of two, principal states. One of these states, viz., that produced by disulfides, and alkylating agents, is stable. The second state, produced by mercury, derivatives, is metastable. At room temperature, it converts, spontaneously, with a half-life of ca. 1 h, to a stable state similar to, that produced by the disulfides and alkylating agents. Demodification of, acetylcholinesterase freshly modified by mercurials, by its exposure to, reduced glutathione, causes rapid release of the bound mercurial, with, concomitant recovery of most of the enzymic activity of the native enzyme., In contrast, similar demodification of acetylcholinesterase modified by, disulfides yields no detectable recovery of enzymic activity., Spectroscopic measurements, employing CD, intrinsic fluorescence, and, binding of 1-anilino-8-naphthalenesulfonate, show that the state produced, initially by mercurials is "native-like", whereas that produced by, disulfides and alkylating agents, and after prolonged incubation of the, mercurial-modified enzyme, is partially unfolded and displays many of the, features of the "molten globule" state. Arrhenius plots show that the, quasi-native state produced by organomercurials is separated by a low (5, kcal/mol) energy barrier from the native state, whereas the partially, unfolded state is separated from the quasi-native state by a high energy, barrier (ca. 50 kcal/mol). Comparison of the 3D structures of native, acetylcholinesterase and of a heavy-atom derivative obtained with HgAc2, suggests that the mercurial-modified enzyme may be stabilized by, additional interactions of the mercury atom attached to the free thiol, group of Cys231, specifically with Ser228O gamma with the main-chain, nitrogen and carbonyl oxygen of the same serine residue.

About this Structure

2J4F is a Single protein structure of sequence from Torpedo californica with HG as ligand. Active as Acetylcholinesterase, with EC number 3.1.1.7 Structure known Active Site: AC1. Full crystallographic information is available from OCA.

Reference

A metastable state of Torpedo californica acetylcholinesterase generated by modification with organomercurials., Kreimer DI, Dolginova EA, Raves M, Sussman JL, Silman I, Weiner L, Biochemistry. 1994 Dec 6;33(48):14407-18. PMID:7981200

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