Binding of MetJ repressor to specific and nonspecific DNA and effect of S-adenosylmethionine on these interactions.

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2010-04-20

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Abstract

We have used analytical ultracentrifugation to characterize the binding of the methionine repressor protein, MetJ, to synthetic oligonucleotides containing zero to five specific recognition sites, called metboxes. For all lengths of DNA studied, MetJ binds more tightly to repeats of the consensus sequence than to naturally occurring metboxes, which exhibit a variable number of deviations from the consensus. Strong cooperative binding occurs only in the presence of two or more tandem metboxes, which facilitate protein-protein contacts between adjacent MetJ dimers, but weak affinity is detected even with DNA containing zero or one metbox. The affinity of MetJ for all of the DNA sequences studied is enhanced by the addition of SAM, the known cofactor for MetJ in the cell. This effect extends to oligos containing zero or one metbox, both of which bind two MetJ dimers. In the presence of a large excess concentration of metbox DNA, the effect of cooperativity is to favor populations of DNA oligos bound by two or more MetJ dimers rather than a stochastic redistribution of the repressor onto all available metboxes. These results illustrate the dynamic range of binding affinity and repressor assembly that MetJ can exhibit with DNA and the effect of the corepressor SAM on binding to both specific and nonspecific DNA.

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10.1021/bi902011f

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Augustus, Anne M, Harvey Sage and Leonard D Spicer (2010). Binding of MetJ repressor to specific and nonspecific DNA and effect of S-adenosylmethionine on these interactions. Biochemistry, 49(15). pp. 3289–3295. 10.1021/bi902011f Retrieved from https://hdl.handle.net/10161/4018.

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Spicer

Leonard D. Spicer

University Distinguished Service Professor Emeritus

The focus of this laboratory is the study of structure/function relationships in biological macromolecules and their binding interactions. The principal method we use for system characterization is magnetic resonance spectroscopy. One specific area of interest is the structural characterization of functional domains in proteins which regulate the transcription of DNA coding for biosynthetic enzymes. The system under current investigation is the methionine repressor protein metJ, its corepressor S-adenosylmethionine, and the cognate sequence DNA. This protein, which functions as a dimer, exhibits a recently described DNA binding motif involving insertion of two beta strands into the major groove with additional stabilization of the complex arising from helix contacts at the dimer-dimer interface. We are using a full complement of heteronuclear 3D and 4D NMR methods to aid in the assignment of the main chain of the metJ repressor. We have recently reported a thermodynamic analysis of the binding interactions of metJ with its cognate DNA and corepressor SAM. We are now developing methods to measure fast proton exchange rates to complement our planned solution structural characterization. We have just initiated another project in collaboration with scientists at the Pacific Northwest National Laboratory to study macromelecular structures of DNA repair proteins in the nucleotide excision repair pathway. The first components of this critical supramacromolecular assembly we are investigating involve the DNA binding domain of the XPA protein for which we are determining the global fold in solution by NMR. Our program also includes a systematic approach to characterizing the conformational preferences of a number of sequentially related peptides developed by Dr. Barton Haynes' laboratory as candidate vaccines for HIV. The peptides consist of a fusion of two noncontiguous segments of the HIV protein gp120. Our goal is to establish whether structural conformers in solution contribute to peptide immunogenicity. We have finished a careful conformational analysis of the initial four peptides and are now correlating the conformer similarities and differences with immunogenic properties. We have also rationally designed several new peptides based on structural criteria and corresponding structural homology to the heavy fragment of IgA proteins. Initial NMR analysis and immunogenic response to three of the designed mutants indicate the rational design of preferred conformers was successful, but raised some novel questions regarding function of immunogenic peptides. We have also just begun a study of solution conformations of the hypoglycosylated tumor specific epitope repeat unit of human mucin and a promising mutant identified by Dombrowski and Wright. This epitope is common to breast and other adenocarcinomas and regulation of tumor specific lymphoid cells responding to this immunogen may be an important step in tumor control. Another protein under investigation is a functional core packing mutant of thioredoxin. We have fully characterized backbone chain dynamics to assess the impact of this mutation on molecular motions and are currently determining its high resolution tertiary structure. Currently, we are also using this mutant to demonstrate a new approach to global fold determination using a minimum set of long range NMR constraints. Finally, as an essential part of these studies, we are developing and have reported new 3- and 4-dimensional NMR experiments and heteronuclear filters for application to large protein systems and binding complexes.

Finally, the core activities of the NMR Center staff have continued to progress rapidly and enhancements to the state-of-the-art instrumentation have again been incorporated. A new deuteration strategy for assignment and study of large proteins by NMR has been developed and used to characterize one of the largest protein monomer reported to date, human carbonic anhydrase. We have also shown that we can observe the longest range distance constraints to date from NOESY correlations which are important in determining tertiary structure of proteins and we are examining the efficacy of structure determinations based on using these critical but limited constraints.


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