Binding of metal cyanide complexes to bovine liver rhodanese in the crystalline state

Abstract

Bovine liver rhodanese, which catalyzes the transfer of sulfur atoms between a variety of sulfur donor and sulfur acceptor substrates, is inhibited by metal cyanide complexes [Volini, M., Van Sweringen, B., & Chen, F.-Sh. (1978) Arch. Biochem. Biophys. 191, 205-215]. Crystallographic studies are described which reveal the binding mode of four different metal cyanides to bovine liver rhodanese: Na[Au(CN2], K2[Pt(CN)4], K2[Ni(CN)4], and K2[Zn(CN)4]. It appears that these complexes bind at one common site at the entrance of the active site pocket, interacting with the positively charged side chains of Arg-186 and Lys-249. This observation explains the inhibition of rhodanese by this class of compounds. For the platinum and nickel cyanide complexes virtually no other binding sites are observed. The gold complex binds, however, to three additional cysteine residues, thereby also displacing the extra sulfur atom which was bound to the essential Cys-247 in the sulfur-rhodanese complex. The zinc complex binds to completely different additional sites and forms complexes with the side chains of Asp-101 and His-203. Possible reasons for these different binding modes are discussed in terms of the preference for "hard" and "soft" ligands of these four metal ions.

Differences in the binding of sulfate, selenate and thiosulfate ions to bovine liver rhodanese, and a description of a binding site for ammonium and sodium ions

“…4 -7). This corresponds well with studies of metalcyanide binding by bovine liver rhodanese [30]. There, the metal cyanides block the access to the essential Cys-247 by binding at a position which is essentially that of the active-site sulfate ion described in the present study.…”

“…7). It is not observed in any of the other difference Fouriers described in this paper, nor in the four difference Fouriers of metal-cyanide complexes in which either K + or Na' has been the counter ion [30]. It is centered around a position which corresponds with a solvent molecule indicated as an ammonium ion in the MIRAS electron density map [31] on the basis of the nature of its ligands.…”

“…A third possibility is that a covalent complex 0 -0-S-S-S-SCys-247 has been formed. Val-72 undergoes a conformational change due to the smaller radius of the Na' ion compared with the NHZ ion [30]. The cation-binding site is labeled as 'H20-312'.…”

Structure of Sulfur-Substituted Rhodanese at 1.36 Å Resolution

“…The sulfate ion is known to be a strong inhibitor of the sulfur transfer reaction catalyzed by rhodanese. It has been suggested that its interaction with the positively charged side chains of Arg186 and Lys249 would block access and correct orientation at the active site of the two negatively charged enzyme substrates thiosulfate and cyanide Lijk et al, 1983). Consistent with this hypothesis, the reaction catalyzed by rhodanese in the crystalline state is greatly accelerated upon replacement of ammonium sulfate with PEG as precipitant in the crystal-suspending medium (R. Berni, unpublished observations).…”

On the mechanism and rate of gold incorporation into thiol-dependent flavoreductases

“…In these complexes gold is usually coordinated by a Cys residue and by an external ligand (e.g. cyanide): this occurs in rhodanese, whose gold complexes have been characterized by X-ray crystallography [12], cathepsin B [13], and albumin [14]. Sec may form similar complex as observed in the case of glutathione peroxidase [15].…”