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MinK potassium channels are heteromultimeric complexes
K K Tai1, K W Wang, S A Goldstein
1Department of Pediatrics, Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, Connecticut 06536-0812, USA.
Abstract:
MinK is a transmembrane protein of 130 amino acids found in the kidney, heart, and vestibular system of mammals. Its expression in Xenopus laevis oocytes induces a voltage-dependent potassium current similar to that seen in vivo. Indirect evidence has fueled speculation that function requires association of MinK and another protein endogenous to oocytes and native tissues. In this report, we show that direct covalent modification of an oocyte membrane protein alters properties of the MinK ion conduction pore; modified channels exhibit decreased potassium conduction and increased permeability to sodium and cesium. The modifying reagents, two membrane-impermeant, sulfhydryl-specific methanethiosulfonate derivatives, react only from the extracellular solution at rates that are determined by the conformational state of the channel. These findings indicate that MinK is intimately associated with an oocyte protein whose exposure to the external solution changes during channel gating and which acts with MinK to establish ion conduction pore function.
Insights
The potassium channel MinK (Mink) requires an associated oocyte protein for proper function. Modifying this protein changes the ion pore, affecting potassium, sodium, and cesium flow.
Area of Science:
- Molecular biology
- Ion channel physiology
- Biochemistry
Background:
- MinK is a transmembrane protein crucial for potassium currents in mammals.
- Its function in Xenopus laevis oocytes suggests interaction with endogenous proteins.
- Previous studies hinted at, but did not confirm, MinK's association with other proteins.
Purpose of the Study:
- To investigate the role of associated proteins in MinK ion channel function.
- To determine if MinK directly interacts with oocyte membrane proteins.
- To characterize the functional consequences of modifying such associated proteins.
Main Methods:
- Expression of MinK in Xenopus laevis oocytes.
- Covalent modification of oocyte membrane proteins using sulfhydryl-specific methanethiosulfonate derivatives.
- Electrophysiological analysis of ion currents (potassium, sodium, cesium) through modified channels.
Main Results:
- Direct covalent modification of an oocyte membrane protein altered MinK channel properties.
- Modified channels showed reduced potassium conduction.
- Increased permeability to sodium and cesium ions was observed in modified channels.
- Modification rates depended on the channel's conformational state, indicating extracellular accessibility.
Conclusions:
- MinK intimately associates with an endogenous oocyte protein.
- This associated protein's extracellular exposure varies with channel gating.
- The oocyte protein is essential for establishing the ion conduction pore function of MinK.