MPS-1 is a K+ channel β-subunit and a serine/threonine kinase

Abstract

We report the first example of a K⁺ channel β-subunit that is also a serine/threonine kinase. MPS-1 is a single–transmembrane domain protein that coassembles with voltage-gated K⁺ channel KVS-1 in the nervous system of the nematode Caenorhabditis elegans. Biochemical analysis shows that MPS-1 can phosphorylate KVS-1 and other substrates. Electrophysiological analysis in Chinese hamster ovary (CHO) cells demonstrates that MPS-1 activity leads to a significant decrease in the macroscopic current. Single-channel analysis and biotinylation assays indicate that MPS-1 reduces the macroscopic current by lowering the open probability of the channel. These data are consistent with a model that predicts that the MPS-1–dependent phosphorylation of KVS-1 sustains cell excitability by controlling K⁺ flux.