QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online 9 September 2003
doi: 10.1242/jcs.00720

This Article Figures Only Full Text Full Text (PDF) All Versions of this Article: jcs.00720v1 116/21/4319    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hathaway, H. J. Articles by Shur, B. D. Search for Related Content PubMed PubMed Citation Articles by Hathaway, H. J. Articles by Shur, B. D.

Mutational analysis of the cytoplasmic domain of ß1,4-galactosyltransferase I: influence of phosphorylation on cell surface expression

Helen J. Hathaway^1,2,3,*, Susan C. Evans^3,*,, Daniel H. Dubois³, Cynthia I. Foote¹, Brooke H. Elder¹ and Barry D. Shur^1,3,

¹ Department of Cell Biology, Emory University School of Medicine, Atlanta, GA, USA
² Department of Cell Biology and Physiology, University of New Mexico School of Medicine, Albuquerque, NM, USA
³ Department of Biochemistry and Molecular Biology, University of Texas M.D. Anderson Cancer Center, Houston, TX, USA

Author for correspondence (e-mail: barry{at}cellbio.emory.edu)

Accepted 20 June 2003

ß1,4-Galactosyltransferase I (GalT I) exists in two subcellular compartments where it performs two distinct functions. The majority of GalT I is localized in the Golgi complex where it participates in glycoprotein biosynthesis; however, a small portion of GalT I is expressed on the cell surface where it functions as a matrix receptor by binding terminal N-acetylglucosamine residues on extracellular glycoside ligands. The GalT I polypeptide occurs in two alternate forms that differ only in the length of their cytoplasmic domains. It is thought that the longer cytoplasmic domain is responsible for GalT I function as a cell surface receptor because of its ability to associate with the detergent-insoluble cytoskeleton. In this study, we demonstrate that the long GalT I cytoplasmic and transmembrane domains are capable of targeting a reporter protein to the plasma membrane, whereas the short cytoplasmic and transmembrane domains do not have this property. The surface-localized GalT I reporter protein partitions with the detergent-insoluble pool, a portion of which co-fractionates with caveolin-containing lipid rafts. Site-directed mutagenesis of the cytoplasmic domain identified a requirement for serine and threonine residues for cell surface expression and function. Replacing either the serine or threonine with aspartic acid reduces surface expression and function, whereas substitution with neutral alanine has no effect on surface expression or function. These results suggest that phosphorylation negatively regulates GalT I function as a surface receptor. Consistent with this, phosphorylation of the endogenous, full-length GalT I inhibits its stable expression on the cell surface. Thus, the 13 amino acid extension unique to the long GalT I isoform is required for GalT I expression on the cell surface, the function of which is regulated by phosphorylation.

Key words: Galactosyltransferase, Cytoplasmic domain, Cell surface, Phosphorylation

This article has been cited by other articles:

				M. J. Wassler, B. D. Shur, W. Zhou, and Y.-J. Geng Characterization of a Novel Ubiquitin-Conjugating Enzyme That Regulates {beta}1,4-Galactosyltransferase-1 in Embryonic Stem Cells Stem Cells, August 1, 2008; 26(8): 2006 - 2018. [Abstract] [Full Text] [PDF]

				B. E. Schaub, B. Berger, E. G. Berger, and J. Rohrer Transition of Galactosyltransferase 1 from Trans-Golgi Cisterna to the Trans-Golgi Network Is Signal Mediated Mol. Biol. Cell, December 1, 2006; 17(12): 5153 - 5162. [Abstract] [Full Text] [PDF]