Optical activity associated with the sulfur to metal charge transfer bands of Zn and Cd GAL4

Abstract

The N-terminal DNA-binding domain of the GAL4 transcription factor, isolated as a proteolytic fragment of 63 amino acid residues, GAL4(63), or cloned as a 62-residue subdomain, GAL4(62*), binds 2 Cd(I1) ions. Both Cd derivatives show intense ellipticity bands associated with -S-"+ Cd charge transfer bands at 250 nm (+), 233 nm , 1987, Biochemistry 26, 6287-6292). Circular dichroism provides further evidence that the GAL4 DNA-binding domain forms a binuclear Cd cluster with the amino acid sequence ~~1 1~~~~~1 4~~~~~2 1~~~~ found in GAL4(62*). Zn2GAL4(62*) has much weaker ellipticity associated with the higher energy -S-"+ Zn charge transfer bands. Removal of the metal ions from GAL4(62*) results in substantial changes in the near UV circular dichroism due to both loss of the charge transfer bands and changes in the conformation of the peptide backbone. Binding of the UASG enhancer DNA element to either Zn or Cd GAL4(62*) alters the ellipticity of the -S-+ metal charge transfer bands suggesting that DNA binding is associated with some changes in conformation around the metal cluster.

Co(II) and Cd(II) Substitute for Zn(II) in the Zinc Finger Derived from the DNA Repair Protein XPA, Demonstrating a Variety of Potential Mechanisms of Toxicity

“…220 nm (Figures 3 and 4). These features are very similar to those observed for the dicadmium cluster in the GAL4 transcription factor and in the Cd(II)-saturated metallothionein (MT), except for the absence of a positive spectral feature at 250 nm in Cd(II)-XPAzf (13,22). On the other hand, the CD spectra of low-occupancy Cd(II)-MT complexes are characterized by a single, broad feature around 240 nm.…”

Identification of cysteine ligands in metalloproteins using optical and NMR spectroscopy: Cadmium‐substituted rubredoxin as a model [Cd(CysS)4]2‐ center

“…These metal-induced features have been observed previously in a number of Cd-substituted metalloproteins where such thiolate coordination exists, e.g., metallothionein, liver alcohol dehydrogenase (LADH), GAL4 protein, etc. (Kagi & Vallee, 1961;Sytkowski & Vallee, 1979;Basile & Coleman, 1992). However, no attempt has been made to use these features quantitatively.…”

ZnIIand HgIIbinding to a designed peptide that accommodates different coordination geometries

“…As hinted already for Hg II , influences of the S − -Zn 2+ chromophore and the peptide secondary structure may be superposed in the observed CD-pattern of Zn II -protein/peptide structures. 34,55,56 Nevertheless, the direction of the observed changes is rather similar to the Zn II -induced effects on the conformation of a phytochelatin analogue 47 and other relatively short oligopeptides 52,58 and may suggest an increasing helical content 47,52 in the Zn II -bound HS. It was proposed that different coordination properties of metal ions may develop selectivity in the stabilization of the α-helical conformation of 20-mer peptides.…”

“…8 One, however, has to bear in mind that due to the high energy ligand to metal charge transfer bands of the Hg II -bound species, CD features of these bands may overlap with the backbone-related CD-effects. This is a known problem in the interpretation of the secondary structures of metalloproteins and metal ion-peptide complexes, 34,45,55,56 particularly when relatively small molecules, like the present 12-mer HS peptide, are studied. Distinction of the different contributions may be easier when thiolate to metal ion transitions appear separately at lower energies compared to the peptide backbone bands, like in the tetrahedral {CysS 4 } type Hg II -rubredoxin complex 31 or in metallothioneins, where metal induced bands dominate the wavelength region above 220-230 nm.…”