A retroviral Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys peptide binds metal ions: spectroscopic studies and a proposed three-dimensional structure.

Abstract

Retroviral gag gene-encoded core nucleic acid binding proteins contain either one or two sequences of the form Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys. Previously, one of us has proposed that these sequences form metal-binding domains in analogy with the "zinc ringer" domains first observed in transcription factor MA. We report that an 18-amino acid peptide derived from the core nucleic acid binding protein from Rauscher murine leukemia virus binds metal ions such as Co2' and Zn2+. The absorption spectrum of the peptide-Co2 complex is highly suggestive of tetrahedral coordination involving three cysteinates and one histidine. Titration experiments indicate that the dissociation constant for the peptideCo2+ complex is 1.0 ,uM and that Zn2+ binds more tightly than Co2+. A detailed three-dimensional structure for this domain based on conserved substructures in other crystallographically characterized metalloproteins and on a detailed analysis of the Cys-Xaa2-Cys-Xaa4-His-Xaa4-Cys sequences from retroviruses and other related sources is proposed.In 1985, two groups observed the occurrence of nine tandem sequences of the form Cys-Xaa4-Cys-Xaa12-His-Xaa3-His in the deduced amino acid sequence of Xenopus transcription factor IIIA (TFIIIA) (1,2). Based on the presence of zinc in a purified TFIIIA-5S RNA complex (1, 3), it was proposed that each of these sequences forms a metal-binding domainthat is, a relatively discrete structural unit stabilized by the tetrahedral coordination of a zinc ion to the invariant cysteine and histidine residues. These domains were termed "zinc fingers" (1). Subsequently, numerous other deduced protein sequences have been found that contain quite similar sequences that match the template described above (4-6).Where it is known, the function of these proteins is to act as specific nucleic acid binding proteins. Studies with several proteins have revealed that zinc is required for this activity (3,(7)(8)(9). The hypothesis that these sequences do indeed form metal-binding domains has been amply supported by a wide variety ofmethods including limited proteolysis studies ofthe TFIIIA-SS RNA complex (1), extended x-ray absorption fine structure spectroscopic studies of the zinc sites in the TF-IIIA-5S RNA complex (10), studies of the structure of the TFIIIA gene (11), hydroxyl radical footprinting studies of a series of shortened versions of TFIIIA on a 5S RNA gene (12), and studies of single domain peptides (13,14 (20) that appear to share the property that they undergo a reverse transcription step at some point in their life cycles (21). The importance ofthe conserved cysteine and histidine residues for viral replication has been directly demonstrated by site-directed mutagenesis in two systems (22,23). Results obtained by using a radioactive zinc blotting technique indicated that these proteins have an affinity for zinc under certain conditions (24). We report herein that an 18-amino acid sequence Asp-Gln-Cys-Ala-Tyr-Cys-Lys-Glu-LysGly-His-Trp-Ala-Lys-Asp-Cys-Pro-Lys derived from the sequence o...

A Novel Zinc-Binding Domain Is Essential for Formation of the Functional Junín Virus Envelope Glycoprotein Complex

“…Taken together, our studies provide strong biochemical evidence for a cysteine-and histidine-containing zinc-finger-like motif in the CTD of G2 and for its essential role in SSP incorporation in the tripartite GP-C complex. Although many viruses have adopted zinc fingers in their structural, regulatory, and catalytic proteins (25,47,57,62,67), the motif has not been described in a virus envelope glycoprotein. In addition to its involvement in SSP association, the unusual ZBD in G2 protein may participate in functions typically served by the CTD of viral envelope glycoproteins, including roles in the intracellular trafficking and membrane fusion activity of GP-C and in virion assembly and budding.…”

Retroviral nucleocapsid proteins possess potent nucleic acid strand renaturation activity

“…retroviral-type zinc-finger Cys,His motifs (Henderson et al, 1981;Berg, 1986), which can be reconstituted with Zn(II), Cd(II), and Co(I1) in vitro (Green & Berg, 1989;Roberts et al, 1989;South et al, 1989;Fitzgerald & Coleman, 1991;. Recent studies provide evidence that these Zn(I1) domains are present in vivo in mature virus preparations Summers et al, 1992).…”

Zinc‐ and sequence‐dependent binding to nucleic acids by the N‐terminal zinc finger of the HIV‐1 nucleocapsid protein: NMR structure of the complex with the Psi‐site analog, dACGCC

“…Subsequent to assembly and budding, the gag poly (Berg, 1986) that the arrays function by coordinating zinc (Green & Berg, 1989Roberts et al, 1989;South et al, 1989South et al, , 1990a South et al, ,b, 1991Summers et al, 1990Summers et al, , 1992Fitzgerald & Coleman, 1991;Omichinski et al, 1991). In particular, recent zinc-edge extended X-ray absorption fine structure (EXAFS) measurements on intact retroviruses reveal that tightly associated viral zinc, which is present in quantities sufficient to populate the arrays , is coordinated t o the CCHC zinc fingers of the NC proteins in mature virions Summers et al, 1992).…”