THE USE OF CD-113 NMR CHEMICAL-SHIFTS AS A STRUCTURAL PROBE IN TETRATHIOLATE METALLOPROTEINS

A wide range of Cd-113 chemical shifts has been observed for Cd-113-su bstituted metalloproteins ranging from -100 ppm, for Cd with octahedra l oxygen ligands, to +760 ppm for tetrahedral sulfur ligands. In parti cular the Cd-113 chemical shifts of tetrahedral sulfur bound sites, fo r proteins such as rubredoxin and desulforedoxin, appear around 720-74 5 ppm, New Cd-113 chemical shift data for Cd-113-substituted, overexpr essed and mutated homologous desulforedoxin-like Fe(S-Cys)(4) proteins , have been obtained and a correlation between the Cd-113 chemical shi ft and structure at the metal site has been observed. This subtle effe ct of geometry at the metal centre on Cd-113 chemical shifts can be ex plained in terms of an increase in the paramagnetic term for the chemi cal shift of the Cd-113 nucleus as distortion of the tetrathiolate cen tre is increased. (C) 1998 Elsevier Science S.A. All rights reserved.