Stroke-induced neuronal damage is thought to result from the overactivation of N-methy1-D-aspartate receptors (NMDARs) and subsequent production of nitric oxide and other toxic radicals. Postsynaptic density-95 (PSD-95) has been found to assemble a postsynaptic protein complex containing NMDARs and neuronal NO synthase (nNOS). The physical coupling of PSD-95 to nNOS is mediated by the second PDZ domain (PDZ2) of PSD95. The pharmacological significance of this tertiary complex in the occurrence of neurotoxicity has set the stage for this PDZ2 domain to be an attractive target for searching for or designing of therapeutic drugs against stroke....[ Read more ]

Stroke-induced neuronal damage is thought to result from the overactivation of N-methy1-D-aspartate receptors (NMDARs) and subsequent production of nitric oxide and other toxic radicals. Postsynaptic density-95 (PSD-95) has been found to assemble a postsynaptic protein complex containing NMDARs and neuronal NO synthase (nNOS). The physical coupling of PSD-95 to nNOS is mediated by the second PDZ domain (PDZ2) of PSD95. The pharmacological significance of this tertiary complex in the occurrence of neurotoxicity has set the stage for this PDZ2 domain to be an attractive target for searching for or designing of therapeutic drugs against stroke.

Twenty-two traditional Chinese medicinal herbs, which have been used for treating strokes for thousands of years in China, were screened for their PDZ2 perturbation abilities using NMR methods. Aqueous extract of one of the twenty-two herbs, Radix Scutellariae, was identified to significantly perturb the structure of the PDZ2 domain of PSD95. Stepwise titration against PDZ2 with the crude extract of Radix Scutellariae demonstrated that the significant perturbation of the PDZ2 structure specifically occurred in its canonical binding pocket. Purification of the "active" components in the aqueous extract of Radix Scutellariae was performed by preparative HPLC and phytochemical methods. Four flavones, which were structurally very similar, were isolated and identified as baicalin (A), norwogonoside (B), oroxylin A-glucuronide (C), and wogonoside (D), respectively. Compound A (baicalin) and compound B (norwogonoside) similarly displayed the most significant PDZ2 perturbation ability, while the remaining two compounds (C&D) were 3-4 fold less potent. The data suggest that these four identified compounds almost fully account for the binding activity of the aqueous extract of Radix Scutellariae.

The identification of small molecules that could bind to PDZ2 domain in this work might provide a new perspective for understanding of the binding mode of PDZ domains, while at the same time providing leads for the development of drugs that might specifically interact with the signaling pathways mediated by PDZ domains.