Interdomain chaperoning between PSD-95, Dlg, and Zo-1 (PDZ) domains of glutamate receptor-interacting proteins.

Qiang Zhang,Mingjie Zhang,Jing-Song Fan

doi:10.1074/jbc.m105996200

Abstract

The multiple PSD-95, Dlg, and Zo-1 (PDZ) domain protein, glutamate receptor-interacting protein (GRIP), is involved in the clustering and trafficking of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor by directly binding to the cytoplasmic tail of the receptor's GluR2 subunit. Both the forth and fifth PDZ domains (PDZ4 and PDZ5) of GRIP are required for effective binding to the receptor. Using NMR and circular dichroism spectroscopic techniques, we show that PDZ5 is completely unstructured in solution. Freshly prepared PDZ4 is largely folded, but the domain can spontaneously unfold. Neither PDZ4 nor PDZ5 binds to GluR2 in solution. Unexpectedly, when PDZ4 and PDZ5 are covalently connected (i.e. PDZ45), both PDZ domains become well folded and stable in solution. The covalent linkage of the two PDZ domains is essential for proper folding of the tandem PDZ domains and its effective binding to GluR2. The interdomain chaperoning effect observed in the PDZ domains of GRIP represents a previously uncharacterized function of PDZ domains.

Highlights

Ion channels and receptors are typically clustered and localized at the specific subcellular sites of neurons such as synapses
Individual PDZ Domains of PDZ4 and PDZ5 Are Unstable and Do Not Interact with GluR2—To dissect functional roles of PDZ4 and PDZ5 of glutamate receptor-interacting protein (GRIP) in binding to GluR2, we studied the structure of the individual PDZ domains in solution
The most important discovery of this work is that PDZ domains in GRIP mutually chaperone each other, enabling the tandem PDZ domains (PDZ45 of GRIP) to interact with its target (GluR2)

Summary

Introduction

Ion channels and receptors are typically clustered and localized at the specific subcellular sites of neurons such as synapses. Interaction between AMPA receptor and a pair of multiple PDZ proteins, GRIP and ABP, is mediated by the GluR2 subunit of the receptor [13, 18]. The requirement of two PDZ domains for proper function is certainly not unique to GRIP proteins. Both in vitro syntenin-syndecan binding and proper membrane localization of syntenin require the paired PDZ domains of syntenin [23, 24]. The first and second PDZ domains of hDlg together are essential for its binding to cytoskeletal protein 4.1 [25] These emerging observations suggest that tandemly arranged PDZ repeats possess functional features that differ from the simple sum of the properties of the individual PDZ domains. The results presented in this work expand our current knowledge of the functional roles of PDZ domains

Methods

Results

Conclusion