RESUMEN
Transcriptional activation and repression via the transcription factors p53 and p65 are mediated by hydrophobic short linear motifs (FXX phi phi) in their activation domains (ADs). To understand the molecular basis for specificity in binding to disparate biological targets, a series of chimeric peptides was synthesized, with sequences derived from the ADs of p53, which binds both the general transcriptional machinery and the repressor protein MDM2, and p65, which is reported to bind the general transcriptional machinery but not MDM2. The FXX phi phi motifs of p53 and p65 differ by only two residues, whereas the flanking sequences have no sequence identity. The affinities of the chimeric peptides to MDM2(25-117) and hTAF(II)31(1-140) were determined. Specificity for binding MDM2 via FXX phi phi motifs derives almost entirely from Trp23 of p53, with a 3.0 kcal mol(-1) loss of binding energy when Trp23 is changed to p65-derived Leu. The identity of the N-terminal flanking sequence did not significantly affect binding to MDM2. In contrast, replacement of the C-terminal sequence of p53 with that of p65 increased the affinity of the chimera for MDM2 by 1.1 kcal mol(-1), contrary to expectations. Replacement of the highly conserved residue Pro27 of p53 with Ser from p65 resulted in a 2.3 kcal mol(-1) improvement in binding to MDM2, generating a ligand (p53-P27S) (Kd = 4.7 nM) that exhibits the highest MDM2 affinity observed for a genetically encodable ligand. The basis for the increased affinity of p53-P27S over p53 was examined by circular dichroism and nuclear magnetic resonance. Pro27 disrupts the recognition alpha-helix of p53, with p53-P27S significantly more alpha-helical than p53.
Asunto(s)
Sustitución de Aminoácidos , Proteínas Proto-Oncogénicas c-mdm2/química , Factores Asociados con la Proteína de Unión a TATA/química , Factor de Transcripción ReIA/química , Factor de Transcripción TFIID/química , Proteína p53 Supresora de Tumor/química , Secuencias de Aminoácidos/genética , Animales , Humanos , Resonancia Magnética Nuclear Biomolecular/métodos , Péptidos/química , Péptidos/genética , Péptidos/metabolismo , Unión Proteica/genética , Estructura Terciaria de Proteína/genética , Proteínas Proto-Oncogénicas c-mdm2/genética , Proteínas Proto-Oncogénicas c-mdm2/metabolismo , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Factores Asociados con la Proteína de Unión a TATA/genética , Factores Asociados con la Proteína de Unión a TATA/metabolismo , Termodinámica , Factor de Transcripción ReIA/genética , Factor de Transcripción ReIA/metabolismo , Factor de Transcripción TFIID/genética , Factor de Transcripción TFIID/metabolismo , Transcripción Genética/genética , Activación Transcripcional/genética , Proteína p53 Supresora de Tumor/genética , Proteína p53 Supresora de Tumor/metabolismoRESUMEN
Cis-trans isomerization of amide bonds plays critical roles in protein molecular recognition, protein folding, protein misfolding, and disease. Aromatic-proline sequences are particularly prone to exhibit cis amide bonds. The roles of residues adjacent to a tyrosine-proline residue pair on cis-trans isomerism were examined. A short series of peptides XYPZ was synthesized and cis-trans isomerism was analyzed. Based on these initial studies, a series of peptides XYPN, X = all 20 canonical amino acids, was synthesized and analyzed by NMR for i residue effects on cis-trans isomerization. The following effects were observed: (a) aromatic residues immediately preceding Tyr-Pro disfavor cis amide bonds, with K(trans/cis)= 5.7-8.0, W > Y > F; (b) proline residues preceding Tyr-Pro lead to multiple species, exhibiting cis-trans isomerization of either or both X-Pro amide bonds; and (c) other residues exhibit similar values of K(trans/cis) (= 2.9-4.2), with Thr and protonated His exhibiting the highest fraction cis. beta-Branched and short polar residues were somewhat more favorable in stabilizing the cis conformation. Phosphorylation of serine at the i position modestly increases the stability of the cis conformer. In addition, the effect of the i+3 residue was examined in a limited series of peptides TYPZ. NMR data indicated that aromatic residues, Pro, Asn, Ala, and Val at the i+3 residue all favor cis amide bonds, with aromatic residues and Asn favoring more compact phi at Tyr(cis) and Ala and Pro favoring more extended phi at Tyr(cis). D-Alanine at the i+3 position particularly disfavors cis amide bonds.