H. Tochio et al., Formation of nNOS/PSD-95 PDZ dimer requires a preformed beta-finger structure from the nNOS PDZ domain, J MOL BIOL, 303(3), 2000, pp. 359-370
PDZ domains are modular protein units that play important roles in organizi
ng signal transduction complexes. PDZ domains mediate interactions with bot
h C-terminal peptide ligands and other PDZ domains. Here, we used PDZ domai
ns from neuronal nitric oxide synthase (nNOS) and postsynaptic density prot
ein-95 (PSD-95) to explore the mechanism for PDZ-dimer formation. The nNOS
PDZ domain terminates with a similar to 30 residue amino acid beta -finger
peptide that is shown to be required for nNOS/PSD-95 PDZ dimer formation. L
n addition, formation of the PDZ dimer requires this beta -finger peptide t
o 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 a
nd stabilizes the beta -hairpin structure of the nNOS PDZ domain. In apo-nN
OS, the beta -finger peptide is partially flexible and adopts a transient b
eta -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 a
lso 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-ra
y crystallography. (C) 2000 Academic Press.