Gating of the shaker potassium channel is modulated differentially by N-glycosylation and sialic acids.
N-linked glycans, including sialic acids, are integral components of ion channel complexes. To determine if N-linked sugars can modulate a rapidly inactivating K+ channel, the glycosylated Drosophila melanogaster Shaker K+ channel (ShB) and the N-glycosylation-deficient mutant (ShNQ), were studied under conditions of full and reduced sialylation. Through an apparent electrostatic mechanism, full sialylation induced uniform and significant hyperpolarizing shifts in all measured voltage-dependent ShB gating parameters compared to those measured under conditions of reduced sialylation. Steady-state gating of ShNQ was unaffected by changes in sialylation and was nearly identical to that observed for ShB under conditions of reduced sialylation, indicating that N-linked sialic acids were wholly responsible for the observed effects of sialic acid on ShB gating. Interestingly, the rates of transition among channel states and the voltage-independent rates of activation and inactivation were significantly slower for ShNQ compared to ShB. Both effects were independent of sialylation, indicating that N-linked sugars other than sialic acids alter ShB gating kinetics but have little to no effect on the steady-state distribution of channels among states. The effect of sialic acids on channel gating, particularly inactivation gating, and the impact of other N-linked sugars on channel gating kinetics are unique to the ShB isoform. Thus, ShB gating is modulated by two complementary but distinct sugar-dependent mechanisms, (1) an N-linked sialic acid-dependent surface charge effect and (2) a sialic acid-independent effect that is consistent with N-linked sugars affecting the stability of ShB among its functional states.
Department of Molecular Pharmacology and Physiology and Programs in Neuroscience and Cardiovascular Sciences, University of South Florida College of Medicine, Tampa, FL 33612, USA.
Daniel
D
Johnson
Eric S
ES
Bennett
D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004331:Drosophila melanogaster; D004594:Electrophysiology; D005260:Female; D006031:Glycosylation; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D019158:N-Acetylneuraminic Acid / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D051637:Shaker Superfamily of Potassium Channels / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D055672:Static Electricity; D014162:Transfection
D051637:Shaker Superfamily of Potassium Channels; D019158:N-Acetylneuraminic Acid