Effects of substitution of proposed Zn(II) ligand His81 or His64 in phage T4 gene 32 protein: spectroscopic evidence for a novel zinc coordination complex

Mutational analysis of domain II beta of bacteriophage Mu transposase: domains II alpha and II beta belong to different catalytic complementation groups

This study examines the contribution of domain II beta of bacteriophage Mu transposase (A protein), a subdomain of the central catalytic domain II, to the transposition reaction. The properties of several point mutations implicate a role for this domain in facilitating metal-assisted assembly of the synaptic complex, as well as in intramolecular DNA strand transfer. Point mutations as well as deletions in domain II beta can be complemented by those in domain II alpha but not those in domain III alpha. Thus, residues within subdomains II alpha and II beta belong to different catalytic complementation groups.

Structures of zinc finger domains from transcription factor Sp1. Insights into sequence-specific protein-DNA recognition

The carboxyl terminus of transcription factor Sp1 contains three contiguous Cys2-His2 zinc finger domains with the consensus sequence Cys-X2-4-Cys-X12-His-X3-His. We have used standard homonuclear two-dimensional NMR techniques to solve the solution structures of synthetic peptides corresponding to the last two zinc finger domains (Sp1f2 and Sp1f3, respectively) of Sp1. Our studies indicate a classical Cys2-His2 type fold for both the domains differing from each other primarily in the conformation of Cys-X2-Cys (beta-type I turn) and Cys-X4-Cys (beta-type II turn) elements. There are, however, no significant differences in the metal binding properties between the Cys-X4-Cys (Sp1f2) and Cys-X2-Cys (Sp1f3) subclasses of zinc fingers. The free solution structures of Sp1f2 and Sp1f3 are very similar to those of the analogous fingers of Zif268 bound to DNA. There is NMR spectral evidence suggesting that the Arg-Asp buttressing interaction observed in the Zif-268.DNA complex is also preserved in unbound Sp1f2 and Sp1f3. Modeling Sp1-DNA complex by overlaying the Sp1f2 and Sp1f3 structures on Zif268 fingers 1 and 2, respectively, predicts the role of key amino acid residues, the interference/protection data, and supports the model of Sp1-DNA interaction proposed earlier.

Characterization of a cooperativity domain mutant Lys3 --> Ala (K3A) T4 gene 32 protein

The N-terminal "B" domain of T4 gene 32 protein contains a Lys3-Arg4-Lys5 sequence that has been postulated to provide a major determinant for cooperative binding. In this report, the equilibrium binding properties of a Lys3 --> Ala substitution mutant of gp32 (K3A gp32) and described and compared to a set of substitution mutants of Arg4 previously described (Villemain, J. L., and Giedroc, D. P. (1993) Biochemistry 32, 11235-11246) and further characterized here. K3A gp32 exhibits binding behavior which mirrors that of R4Q gp32. Despite an 6-8-fold decrease in overall binding affinity (Kapp = Kint x omega) at pH 8.1, 0.20 M NaCl, 20 degrees C, the magnitude of the cooperativity parameter is at most 2-3-fold smaller than that of the wild-type protein. The magnitude of omega is independent of salt concentration and type over the range in [NaCl] from 0.125 to 0. 225 M and [NaF] between 0.20 and 0.32 M (log omega = 2.86 +/- 0.19). For comparison, log omega for wild-type gp32 is 2.91 (+/- 0.21) resolved at 0.275 M NaCl and 3.39 +/- 0.11 in [NaF] between 0.40 and 0.45 M. In contrast to omega, the [NaCl] dependence of Kapp is large and markedly nonlinear for both wild-type and K3A gp32s over a [NaCl] range extending from 0.05 M to 0.40 M NaCl. Modeling of the complete salt dependence of Kapp for wild-type, K3A, and R4T gp32s in NaCl and NaF with a simple ion-exchange model suggests that substitutions within the basic Lys3-Arg4-Lys5 sequence do not strongly modulate the net displacement of cations and anions upon poly(A) complex formation by gp32.

The metal ion-induced cooperative binding of HIV-1 integrase to DNA exhibits a marked preference for Mn(II) rather than Mg(II)

In this investigation, we examine the interaction between the human immunodeficiency virus type I integrase and oligonucleotides that reflect the sequences of the extreme termini of the viral long terminal repeats (LTRs). The results of gel filtration and a detailed binding density analysis indicate that the integrase binds to the LTR as a high-order oligomer at a density equivalent to 10 +/- 0.8 integrase monomers per 21-base pair LTR. The corresponding binding isotherm displays a Hill coefficient of 2, suggesting that the binding mechanism involves the cooperative interaction between two oligomers. This interaction is quite stable, exhibiting a prolonged half-life (t1/2 approximately 13 h) in the presence of Mn2+ cations. Complexes were less stable when formed with Mg2+ (t1/2 approximately 1 h). The role of Mn2+ appears to be in the induction of the protein-protein interactions that stabilize the bound complexes. In terms of the 3'-end processing of the LTR, similar catalytic rates (kcat approximately 0.06 min-1) were obtained for the stable complex in the presence of either cation. Hence, the apparent preference observed for Mn2+ in standard in vitro integration assays can be attributed entirely to the augmentation in the DNA binding affinity of the integrase.