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J. Biol. Chem., Vol. 275, Issue 39, 30677-30682, September 29, 2000
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From the Department of Physiology and Biophysics, Mount Sinai
School of Medicine, New York, New York 10029
GIRK (G protein-gated
inward rectifier
K+ channel) proteins play critical
functional roles in heart and brain physiology. Using antibodies
directed to either GIRK1 or GIRK4, site-directed mutagenesis, and
specific glycosidases, we have investigated the effects of glycosylation in the biosynthesis and heteromerization of these proteins expressed in oocytes. Both GIRK1 and GIRK4 have one
extracellular consensus N-glycosylation site. Using
chimeras between GIRK1 and GIRK4 as well as a GIRK1
N-glycosylation mutant, we report that GIRK1 was
glycosylated at Asn119, whereas GIRK4 was not glycosylated
at Asn132. GIRK1 membrane-spanning domain 1 was
required for optimal glycosylation at Asn119 because a
chimera that contained GIRK4 membrane-spanning domain 1 significantly
reduced the addition of a carbohydrate structure at this site. This
finding may partly account for the reason that GIRK4 is not
glycosylated at Asn132, either as a homomer or when
coexpressed with GIRK1. When the GIRK1(N119Q) mutant was coexpressed
with GIRK4, the biophysical properties of the heteromeric channel and
the magnitude of the agonist-induced currents were similar to those of
controls. Thus, N-glycosylation of GIRK1 at
Asn119 does not appear to affect its physical association
with GIRK4, the routing of the heteromer to the cell surface, or
heteromeric channel function, unlike the dramatic functional effects of
N-glycosylation of ROMK1 at Asn117 (Schwalbe,
R. A., Wang, Z., Wible, B. A., and Brown, A. M. (1995) J. Biol. Chem. 270, 15336-15340).
Glycosylation of GIRK1 at Asn119 and ROMK1 at
Asn117 Has Different Consequences in Potassium Channel
Function*
,
*
This work was supported by National Institutes of Health
Grants NS29633 (to W. B. T.) and HL54185 (to D. E. L.) and by
American Heart Association Grant-in-aid 96011620 (to D. E. L.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
Present address: Cambridge Neuroscience, Bldg. 100, One Kendall
Square, Cambridge, MA 02139.
§
To whom correspondence may be addressed: Dept. of Physiology and
Biophysics, One Gustave Levy Place, Mount Sinai School of Medicine, New
York, NY 10029. Tel.: 212-241-6285; Fax: 212-860-3369; E-mail:
logo@smtplink.mssm.edu.
¶
To whom correspondence may be addressed: Dept. of Biological
Sciences, Fordham University, Bronx, NY 10458. Tel.: 718-817-3688; Fax:
718-817-3645; E-mail: thornhill@murray.fordham.edu.
Copyright © 2000 by The American Society for Biochemistry and Molecular Biology, Inc.
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