Distinct structural requirements for clustering and immobilization of K+ channels by PSD-95

• Published in: The Journal of general physiology 1999-01, Vol.113 (1), p.71-80
• Main Authors: Burke, N A, Takimoto, K, Li, D, Han, W, Watkins, S C, Levitan, E S
• Format: Article
• Language: English
• Subjects: Animals; Cell Line; Cell Membrane - chemistry; Cell Membrane - metabolism; Cellular biology; Cloning, Molecular; Disks Large Homolog 4 Protein; Green Fluorescent Proteins; Humans; Image Processing, Computer-Assisted; Immunohistochemistry; Intracellular Signaling Peptides and Proteins; Kv1.4 Potassium Channel; Luminescent Proteins - chemistry; Membrane Proteins - chemistry; Nerve Tissue Proteins - chemistry; Potassium Channels - chemistry; Potassium Channels - drug effects; Potassium Channels - genetics; Potassium Channels, Voltage-Gated; Protein Conformation; Proteins; Rats
• ISSN: 0022-1295; 1540-7748
• DOI: 10.1085/jgp.113.1.71

PDZ-domain-containing proteins such as PSD-95 have been implicated in the targeting and clustering of membrane proteins. Biochemical and immunohistochemical studies indicate that PSD-95 recognizes COOH-terminal S/TXV sequences present in Kv1 K+ channels. However, the effect of binding a PDZ domain on a target protein has not been studied in live cells. In the present study, a green fluorescent protein-Kv1.4 fusion protein is used to study the effect of PSD-95 on channel movement. Fluorescence recovery after photobleaching showed that PSD-95 can immobilize K+ channels in the plasma membrane in an all-or-none manner. Furthermore, time lapse imaging showed that channel clusters formed in the presence of PSD-95 are stable in size, shape, and position. As expected from previous reports, two green fluorescent protein-tagged COOH-terminal variants of Kv1.4, Delta15 and V655A, are not clustered by PSD-95. However, coexpression of PSD-95 with V655A, but not Delta15, leads to the appearance of PSD-95 immunoreactivity in the plasma membrane. Furthermore, fluorescence recovery after photobleaching studies show that V655A channels are immobilized by PSD-95. Thus, V655A channels can interact with PSD-95 in a manner that leads to channel immobilization, but not clustering. These experiments document for the first time that PSD-95 immobilizes target proteins. Additionally, the data presented here demonstrate that the structural requirements for protein clustering and immobilization by PSD-95 are distinct.