PHOSPHORYLATION OF CREB AT SER-133 INDUCES COMPLEX-FORMATION WITH CREB-BINDING PROTEIN VIA A DIRECT MECHANISM

We have characterized a phosphoserine binding domain in the coactivato r CREB-binding protein (CBP) which interacts with the protein kinase A -phosphorylated, and hence activated, form of the cyclic AMP-responsiv e factor CREB, The CREB binding domain, referred to as KIX, is or heli cal and binds to an unstructured kinase-inducible domain in CREB follo wing phosphorylation of CREB at Ser-133, Phospho-Ser-133 forms direct contacts with residues in KIX, and these contacts are further stabiliz ed by hydrophobic residues in the kinase-inducible domain which Bank p hospho-Ser-133. Like the src homology 2 (SH2) domains which bind phosp hotyrosine-containing peptides, phosphoserine 133 appears to coordinat e with a single arginine residue (Arg-600) in KIX which is conserved i n the CBP-related protein P300, Since mutagenesis of Arg-600 to Gin se verely reduces CREB-CBP complex formation, our results demonstrate tha t, as in the case of tyrosine kinase pathways, signal transduction thr ough serine/threonine kinase pathways may also require protein interac tion motifs which are capable of recognizing phosphorylated amino acid s.