Protein dimer binding

The protein dimer binds so that the recognition a helices at opposite ends of the protein molecule are in the major groove of the DNA as predicted, where they interact with base pairs at the end of the DNA molecule. Since these binding sites are separated by one turn of the DNA helix, it follows that at the center of the DNA molecule the narrow groove faces the protein... 

ATPase-dependent (Client protein dimerization binding )... 

Approximately 10 base pairs are required to make one turn in B-DNA. The centers of the palindromic sequences in the DNA-binding regions of the operator are also separated by about 10 base pairs (see Table 8.1). Thus if one of the recognition a helices binds to one of the palindromic DNA sequences, the second recognition a helix of the protein dimer is poised to bind to the second palindromic DNA sequence. 

The resulting newly synthesized Cro protein also binds to the operator region as a dimer, but its order of preference is opposite to that of repressor (Figure 39—7). That is, Cro binds most t hdy to Or3, but there is no cooperative effect of Cro at 0 3 on the binding of Cro to 0 2. At increasingly higher concentrations of Cro, the protein will bind to Op 2 and evenmally to OrI. 

Figure 39-13. A schematic representation of the three-dimensional structure of Cro protein and its binding to DNA by its helix-turn-helix motif. The Cro monomer consists of three antiparallel p sheets (P1-P3) and three a-helices (a,-a3).The helix-turn-helix motif is formed because the aj and U2 helices are held at about 90 degrees to each other by a turn offour amino acids. The helix of Cro is the DNA recognition surface (shaded). Two monomers associate through the antiparallel P3 sheets to form a dimer that has a twofold axis of symmetry (right). A Cro dimer binds to DNA through its helices, each of which contacts about 5 bp on the same surface of the major groove. The distance between comparable points on the two DNA a-helices is 34 A, which is the distance required for one complete turn of the double helix. (Courtesy of B Mathews.)...

Actin (band 5) exists in red blood cells as short, dou-ble-hehcal filaments of F-actin. The tail end of spectrin dimers binds to actin. Actin also binds to protein 4.1. 

Complex formation among the three protein components of the M. trichosporium OB3b MMO has been demonstrated (66). In this work, it was hypothesized that protein B binds tightly to Hox to form an activated complex but that, after formation of H, the binding affinity is diminished (63, 66). Results reported for M. capsulatus (Bath) are consistent with initial binding of Hox to protein B to form an activated complex (51), because increased yields and rate constants are seen when protein B is added to Hred. If the Hred-protein B complex of M. capsulatus (Bath) is the species influencing reactivity, then there should be a direct relationship between equivalents of added B and the rate constant, at which point the B-specific binding sites would be saturated. Since H is a dimer two equivalents of protein B... 

Alefacept (Amevive) is a dimeric fusion protein that binds to CD2 on T cells to inhibit cutaneous T-cell activation and proliferation. It also produces a dose-dependent decrease in circulating total lymphocytes. Alefacept is approved for treatment of moderate to severe plaque psoriasis and is also effective for treatment of psoriatic arthritis. Significant response is usually achieved after about 3 months of therapy. The recommended dose is 15 mg intramuscularly once weekly for 12 weeks. Adverse effects are mild and include pharyngitis, flu-like symptoms, chills, dizziness, nausea, headache, injection site pain and inflammation, and nonspecific infection. 

Microtubules have a key role in mitosis and cell-proliferation. They are dynamic assemblies of heterodimers of a and f3 tubullin. In the cell-reproduction cascade tubulin polymerizes fast and subsequently depolymerizes. Tubulin dimers are unusual guanyl nucleotide binding (G) proteins, which bind GTP reversibly at a site in the (3-tubulin. GTP irreversibly hydrolyzes to GDP during polymerization. 

Other multinuclear protein-zinc interactions may be implicated for the GAL4 protein in vivo. For example, since the GAL4 dimer binds to palindromic DNA sequences (Giniger et al, 1985), one possibility is that the dimer interface of the intact protein could comprise three zinc ions tetrahedrally coordinated by the 12 cysteines of two GAL4 monomers... 

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