Sialic acids attached to O-glycans modulate voltage-gated potassium channel gating.
Neuronal, cardiac, and skeletal muscle action potentials are produced and conducted through the highly regulated activity of several types of voltage-gated ion channels. Voltage-gated potassium (K(v)) channels are responsible for action potential repolarization. Glycans can be attached to glycoproteins through N- and O-linkages. Previous reports described the impact of N-glycans on voltage-gated ion channel function. Here, we show that sialic acids attached through O-linkages modulate gating of K(v)2.1, K(v)4.2, and K(v)4.3. The conductance-voltage (G-V) relationships for each isoform were shifted uniquely by a depolarizing 8-16 mV under conditions of reduced sialylation. The data indicate that sialic acids modulate K(v) channel activation through apparent electrostatic mechanisms that promote channel activity. Voltage-dependent steady-state inactivation was unaffected by changes in sialylation. N-Linked sialic acids cannot be responsible for the G-V shifts because K(v)4.2 and K(v)4.3 cannot be N-glycosylated, and immunoblot analysis confirmed K(v)2.1 is not N-glycosylated. Glycosidase gel shift analysis suggested that K(v)2.1, K(v)4.2, and K(v)4.3 were O-glycosylated and sialylated. To confirm this, azide-modified sugar residues involved specifically in O-glycan and sialic acid biosynthesis were shown to incorporate into all three K(v) channel isoforms using Cu(I)-catalyzed cycloaddition chemistry. Together, the data indicate that sialic acids attached to O-glycans uniquely modulate gating of three K(v) channel isoforms that are not N-glycosylated. These data provide the first evidence that external O-glycans, with core structures distinct from N-glycans in type and number of sugar residues, can modulate K(v) channel function and thereby contribute to changes in electrical signaling that result from regulated ion channel expression and/or O-glycosylation.
Department of Molecular Pharmacology and Physiology, University of South Florida College of Medicine, Tampa, Florida 33612, USA.
Tara A
TA
Schwetz
Sarah A
SA
Norring
Andrew R
AR
Ednie
Eric S
ES
Bennett
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D006031:Glycosylation; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D019158:N-Acetylneuraminic Acid / Q000235:genetics / Q000378:metabolism*; D011134:Polysaccharides / Q000235:genetics / Q000378:metabolism*; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000502:physiology*
D011134:Polysaccharides; D015221:Potassium Channels; D019158:N-Acetylneuraminic Acid