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© The Rockefeller University Press, 0021-9525/1998//545 $5.00
The Journal of Cell Biology, Volume 142, Number 2, , 1998 545-555

Articles

Coordination of an Array of Signaling Proteins through Homo- and Heteromeric Interactions Between PDZ Domains and Target Proteins



Xian-Zhong Shawn Xu, Atish Choudhury, Xiaoling Li, and Craig Montell

Department of Biological Chemistry and Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205

The rapid activation and feedback regulation of many G protein signaling cascades raises the possibility that the critical signaling proteins may be tightly coupled. Previous studies show that the PDZ domain containing protein INAD, which functions in Drosophila vision, coordinates a signaling complex by binding directly to the light-sensitive ion channel, TRP, and to phospholipase C (PLC). The INAD signaling complex also includes rhodopsin, protein kinase C (PKC), and calmodulin, though it is not known whether these proteins bind to INAD. In the current work, we show that rhodopsin, calmodulin, and PKC associate with the signaling complex by direct binding to INAD. We also found that a second ion channel, TRPL, bound to INAD. Thus, most of the proteins involved directly in phototransduction appear to bind to INAD. Furthermore, we found that INAD formed homopolymers and the homomultimerization occurred through two PDZ domains. Thus, we propose that the INAD supramolecular complex is a higher order signaling web consisting of an extended network of INAD molecules through which a G protein–coupled cascade is tethered.

Key Words: rhodopsin • TRPL • calmodulin • PKC • PDZ

Abbreviations used in this paper: INAD, inactivation no afterpotential D, PLC, phospholipase C; PKC, protein kinase C.

Address all correspondence to Craig Montell, Department of Biological Chemistry and Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205. Tel.: (410) 955-1199. Fax: (410) 614-9573. E-mail: cmontell{at}bs.jhmi.edu


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