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.
Johnson
Daniel
D
Department of Molecular Pharmacology and Physiology and Programs in Neuroscience and Cardiovascular Sciences, University of South Florida College of Medicine, Tampa, FL 33612, USA.
Bennett
Eric S
ES
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