THE STRUCTURAL BASIS FOR 14-3-3-PHOSPHOPEPTIDE BINDING-SPECIFICITY

The 14-3-3 family of proteins mediates signal transduction by binding to phosphoserine-containing proteins. Using phosphoserine-oriented pep tide libraries to probe all mammalian and yeast 14-3-3s, we identified two different binding motifs, RSXpSXP and RXY/FXpSXP, present in near ly all known 14-3-3 binding proteins. The crystal structure of 14-3-3 zeta complexed with the phosphoserine motif in polyoma middle-T was de termined to 2.6 Angstrom resolution. The bound peptide is in an extend ed conformation, with a tight turn created by the pS +2 Pro in a cia c onformation. Sites of peptide-protein interaction in the complex ratio nalize the peptide library results. Finally, we show that the 14-3-3 d imer binds tightly to single molecules containing tandem repeats of ph osphoserine motifs, implicating bidentate association as a signaling m echanism with molecules such as Raf, BAD, and CbI.