RESUMO
Proteins that recognize specific DNA sequences play a central role in the regulation of transcription. The tremendous increase in structural information on protein-DNA complexes has uncovered a remarkable structural diversity in DNA binding folds, while at the same time revealing common themes in binding to target sites in the genome.
Assuntos
Proteínas de Ligação a DNA/metabolismo , DNA/química , Motivos de Aminoácidos , Animais , Sequência de Bases/genética , DNA/genética , DNA/metabolismo , Proteínas de Ligação a DNA/química , Modelos Moleculares , Conformação de Ácido Nucleico , Ligação Proteica , Dobramento de Proteína , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Zinco/metabolismoRESUMO
Pax5 regulates the B cell-specific expression of the mb-1 gene together with members of the Ets family of transcriptional activators. The Ets proteins on their own bind poorly to the Pax5/Ets binding site, but can be recruited to the site by cooperative interactions with Pax5. The structure of the ETS domain of Ets-1 and the paired domain of Pax5 bound to DNA reveals the molecular details of the selective recruitment of different Ets proteins by Pax5. Comparison with structures of Ets-1 alone bound to both high- and low-affinity DNA sites reveals that Pax5 alters the Ets-1 contacts with DNA. The ability of one protein to alter the DNA sequence-specific contacts of another provides a general mechanism for combinatorial regulation of transcription.
Assuntos
DNA/química , DNA/metabolismo , Conformação de Ácido Nucleico , Proteínas/química , Proteínas/metabolismo , Proteínas Proto-Oncogênicas/química , Proteínas Proto-Oncogênicas/metabolismo , Fatores de Transcrição/química , Fatores de Transcrição/metabolismo , Sequência de Aminoácidos , Sequência de Bases , Sítios de Ligação , Cristalografia por Raios X , DNA/genética , Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/metabolismo , Modelos Moleculares , Dados de Sequência Molecular , Fator de Transcrição PAX5 , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Ligação Proteica , Estrutura Terciária de Proteína , Proteína Proto-Oncogênica c-ets-1 , Proteínas Proto-Oncogênicas c-ets , Especificidade por SubstratoRESUMO
BACKGROUND: The methionine repressor, MetJ, represses the transcription of genes involved in methionine biosynthesis by binding to arrays of two to five adjacent copies of an eight base-pair 'metbox' sequence. Naturally occurring operators differ from the consensus sequence to a greater extent as the number of metboxes increases. MetJ, while accommodating this sequence variation in natural operators, is very sensitive to particular base changes, even where bases are not directly contacted in the crystal structure of a complex formed between the repressor and consensus operator. RESULTS: Here we report the high-resolution structure of a MetJ mutant, Q44K, bound to the consensus operator sequence (Q44Kwt19) and two related sequences containing mutations at sites believed to be important for indirect readout at non-contacted bases. The overall structure of the Q44Kwt19 complex is very similar to the wild-type complex, but there are small variations in sugar-phosphate backbone conformation and direct contacts to the DNA bases. The mutant complexes show a mixture of direct and indirect readout of sequence variations, with differences in direct contacts and DNA conformation. CONCLUSIONS: Comparison of the wild-type and mutant repressor-operator complexes shows that the repressor makes sufficiently strong interactions with the sugar-phosphate backbone to accommodate some variation in operator sequence with minor changes in direct bases contacts. The reduction in repressor affinity for the two mutant repressor complexes can be partially attributed to a loss in direct contacts to the DNA. In one case, however, the replacement of a flexible TA base-step leads to an unfavourable DNA conformation that reduces the stability of the repressor-operator complex.
