PDZ DOMAIN OF NEURONAL NITRIC-OXIDE SYNTHASE RECOGNIZES NOVEL C-TERMINAL PEPTIDE SEQUENCES

PDZ domains are multifunctional protein-interaction motifs that often bind to the C-terminus of protein targets. Nitric oxide (NO), an endog enous signaling molecule, plays critical roles in nervous, immune, and cardiovascular function. Although there are numerous physiological fu nctions for neuron-derived NO, produced primarily by the neuronal NO s ynthase (nNOS), excess nNOS activity mediates brain injury in cerebral ischemia and in animal models of Parkinson's disease. Subcellular loc alization of nNOS activity must therefore be tightly regulated. To det ermine ligands for the PDZ domain of nNOS, we screened 13 billion dist inct peptides and found that the nNOS-PDZ domain binds tightly to pept ides ending Asp-X-Val. This differs from the only known (Thr/Ser)-X-Va l consensus that interacts with PDZ domains from PSD-95. Preference fo r Asp at the -2 peptide position is mediated by Tyr-77 of nNOS. A Y77D 78 to H(77)E(78) substitution changes the binding specificity from Asp -X-Val to Thr-X-Val. Guided by the Asp-X-Val consensus, candidate nNOS interacting proteins have been identified including glutamate and mel atonin receptors. Our results demonstrate that PDZ domains have distin ct peptide binding specificity.