Cg. Giraudo et al., Physical and functional association of glycolipid N-acetyl-galactosaminyl and galactosyl transferases in the Golgi apparatus, P NAS US, 98(4), 2001, pp. 1625-1630
Citations number
24
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Glycolipid glycosyltransferases catalyze the stepwise transfer of monosacch
arides from sugar nucleotides to proper glycolipid accepters. They are Golg
i resident proteins that colocalize functionally in the organelle, but thei
r intimate relationships are not known. Here, we show that the sequentially
acting UDP-GalNAc: lactosylceramide/GM3/GD3 beta -1,4-N-acetyl-galactosami
nyltransferase and the UDP-Gal:GA2/GM2/GD2 beta -1,3-galactosyltransferase
associate physically in the distal Golgi. Immunoprecipitation of the respec
tive epitope-tagged versions expressed in transfected CHO-K1 cells resulted
in their mutual coimmunoprecipitation. The immunocomplexes efficiently cat
alyze the two transfer steps leading to the synthesis of GM1 from exogenous
GM3 in the presence of UDP-GalNAc and UDP-Gal, The N-terminal domains (cyt
osolic tail, transmembrane domain, and few amino acids of the stem region)
of both enzymes are involved in the interaction because (i) they reproduce
the coimmunoprecipitation behavior of the full-length enzymes, (ii) they co
mpete with the full-length counterpart in both coimmunoprecipitation and GM
1 synthesis experiments, and (iii) fused to the cyan and yellow fluorescent
proteins, they localize these proteins to the Golgi membranes in an associ
ation close enough as to allow fluorescence resonance energy transfer betwe
en them. We suggest that these associations may improve the efficiency of g
lycolipid synthesis by channeling the intermediates from the position of pr
oduct to the position of acceptor along the transfer steps.