title: Formation of nNOS/PSD-95 PDZ dimer requires a preformed beta-finger structure from the nNOS PDZ domain.
abstract: PDZ domains are modular protein units that play important roles in organizing signal transduction complexes. PDZ domains mediate interactions with both C-terminal peptide ligands and other PDZ domains. Here, we used PDZ domains from neuronal nitric oxide synthase (nNOS) and postsynaptic density protein-95 (PSD-95) to explore the mechanism for PDZ-dimer formation. The nNOS PDZ domain terminates with a approximately 30 residue amino acid beta-finger peptide that is shown to be required for nNOS/PSD-95 PDZ dimer formation. In addition, formation of the PDZ dimer requires this beta-finger peptide to be physically anchored to the main body of the canonical nNOS PDZ domain. A buried salt bridge between the beta-finger and the PDZ domain induces and stabilizes the beta-hairpin structure of the nNOS PDZ domain. In apo-nNOS, the beta-finger peptide is partially flexible and adopts a transient beta-strand like structure that is stabilized upon PDZ dimer formation. The flexibility of the NOS PDZ beta-finger is likely to play a critical role in supporting the formation of nNOS/PSD-95 complex. The experimental data also suggest that nNOS PDZ and the second PDZ domain of PSD-95 form a "head-to-tail" dimer similar to the nNOS/syntrophin complex characterized by X-ray crystallography.
authors.affiliation: Department of Biochemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, Kowloon, People's Republic of China.
authors.forename: H
authors.initials: H
authors.lastname: Tochio
authors.forename: Y K
authors.initials: YK
authors.lastname: Mok
authors.forename: Q
authors.initials: Q
authors.lastname: Zhang
authors.forename: H M
authors.initials: HM
authors.lastname: Kan
authors.forename: D S
authors.initials: DS
authors.lastname: Bredt
authors.forename: M
authors.initials: M
authors.lastname: Zhang
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D002942:Circular Dichroism; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D019906:Nuclear Magnetic Resonance, Biomolecular; D018583:Pliability; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins; D055672:Static Electricity; D013379:Substrate Specificity; D020349:Surface Plasmon Resonance
chemical_list: D009419:Nerve Tissue Proteins; D011994:Recombinant Proteins; C033652:postsynaptic density proteins; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I