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PROTEIN AND VESICLE TRAFFICKING, CYTOSKELETON

Regulation of cell surface expression of functional pacemaker channels by a motif in the B-helix of the cyclic nucleotide-binding domain

Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, British Columbia, Canada

Submitted 5 February 2008 ; accepted in final form 3 July 2008

Previous studies have suggested that a portion of the cyclic nucleotide-binding domain (CNBD) of the hyperpolarization-activated cyclic nucleotide-gated channel 2 (HCN2) "pacemaker" channel, composed of the A- and B-helices and the interceding β-barrel, confers two functions: inhibition of channel opening in response to hyperpolarization and promotion of cell surface expression. The sequence determinants required for each of these functions are unknown. In addition, the mechanism underlying plasma membrane targeting by this subdomain has been limitedly explored. Here we identify a four-amino acid motif (EEYP) in the B-helix that strongly promotes channel export from the endoplasmic reticulum (ER) and cell surface expression but does not contribute to the inhibition of channel opening. This motif augments a step in the trafficking pathway and/or the efficiency of correct folding and assembly.

pacemaker channel function; protein export; trafficking; hyperpolarization-activated cyclic nucleotide-gated channel