PSD-95 Assembles a Ternary Complex with theN-Methyl-d-aspartic Acid Receptor and a Bivalent Neuronal NO Synthase PDZ Domain

Karen S Christopherson,Brian J Hillier,Wendell A Lim,David S Bredt

doi:10.1074/jbc.274.39.27467

Karen S Christopherson, Brian J Hillier + Show 2 more

Open Access

https://doi.org/10.1074/jbc.274.39.27467

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Abstract

Nitric oxide (NO) biosynthesis in cerebellum is preferentially activated by calcium influx through N-methyl-D-aspartate (NMDA)-type glutamate receptors, suggesting that there is a specific link between these receptors and neuronal NO synthase (nNOS). Here, we find that PSD-95 assembles a postsynaptic protein complex containing nNOS and NMDA receptors. Formation of this complex is mediated by the PDZ domains of PSD-95, which bind to the COOH termini of specific NMDA receptor subunits. In contrast, nNOS is recruited to this complex by a novel PDZ-PDZ interaction in which PSD-95 recognizes an internal motif adjacent to the consensus nNOS PDZ domain. This internal motif is a structured "pseudo-peptide" extension of the nNOS PDZ that interacts with the peptide-binding pocket of PSD-95 PDZ2. This asymmetric interaction leaves the peptide-binding pocket of the nNOS PDZ domain available to interact with additional COOH-terminal PDZ ligands. Accordingly, we find that the nNOS PDZ domain can bind PSD-95 PDZ2 and a COOH-terminal peptide simultaneously. This bivalent nature of the nNOS PDZ domain further expands the scope for assembly of protein networks by PDZ domains.

Highlights

Efficiency and specificity in cellular signaling cascades is often mediated by assembly of multiprotein transduction networks
Binding studies show that both the first and second PDZ repeats in PSD-95 potently interact with the COOH-terminal tails of specific N-methyl-D-aspartic acid (NMDA) receptor subunits and other ion channels that terminate in a consensus Glu-(Ser/Thr)-X-(Val/Ile)-COOH [15,16,17,18]
We demonstrate that neuronal nitric oxide synthase (nNOS), PSD-95, and the NMDA receptor subunit 2B (NR2B) coimmunoprecipitate from brain, and that PSD-95 is sufficient to assemble a tight ternary complex with nNOS and an NR2B fusion protein

Summary

EXPERIMENTAL PROCEDURES

Immunoprecipitation—Rat forebrain was homogenized in 20 volumes (w/v) TEE (25 mM Tris-HCl, pH 7.4, 1 mM EDTA, 1 mM EGTA) containing 1 mM phenylmethylsulfonyl fluoride. Histidine-tagged PSD-95 or nNOS 1–130 were expressed in the bacterial strain BL21(DE3)pLysS (Novagen), solubilized by sonication in 50 mM sodium phosphate buffer (pH 8.0) containing 6 M GdnHCl, 300 mM NaCl, 10% glycerol and purified by cobalt-iminodiacetic acid Sepharose chromatography (Sigma). NNOS constructs encoding fusion proteins with the Gal DNA-binding domain were generated by polymerase chain reaction of the appropriate coding sequence to incorporate EcoRI and BamHI flanking sequences (nNOS 1–100; 1–111; 1–130; 1–130 Y77H, D78E; 1–159; 1–159 V93K) and ligation into pGBT9 (CLONTECH). PSD-95 and PSD-93 constructs encoding fusion proteins with the Gal activation domain were generated by polymerase chain reaction of the appropriate coding sequence to incorporate EcoRI and BamHI flanking sequences (PSD-93 PDZ2, amino acids 117–371; PSD-93 PDZ2 H258V; PSD-95, amino acids 113–364; PSD-95 L241K) and ligation into pGAD424 (CLONTECH). An expression vector encoding the Gal activation domain fused to a 9-residue peptide ending ESDV was generated by cloning the following annealed oligo into pGAD424 digested with EcoRI and BamHI: 5Ј-AATTCAAGCTTTCTAGTATTGAGTCTGATGTCTGAG-3Ј and 5Ј-GATCCTCAGACATCAGACTCAATACTAGAAAGCTTG-3Ј

RESULTS

These data clearly demonstrate that the nNOS PDZ domain

DISCUSSION