The ER protein folding sensor UDP-glucose glycoprotein-glucosyltransferase modifies substrates distant to local changes in glycoprotein conformation.
We present in vitro data that explain the recognition mechanism of misfolded glycoproteins by UDP-glucose glycoprotein-glucosyltransferase (UGGT). The glycoprotein exo-(1,3)-beta-glucanase (beta-Glc) bearing two glycans unfolds in a pH-dependent manner to become a misfolded substrate for UGGT. In the crystal structure of this glycoprotein, the local hydrophobicity surrounding each glycosylation site coincides with the differential recognition of N-linked glycans by UGGT. We introduced a single F280S point mutation, producing a beta-Glc protein with full enzymatic activity that was both recognized as misfolded and monoglucosylated by UGGT. Contrary to current views, these data show that UGGT can modify N-linked glycans positioned at least 40 A from localized regions of disorder and sense subtle conformational changes within structurally compact, enzymatically active glycoprotein substrates.
Taylor
Sean C
SC
Biochemistry Department, Faculty of Medicine, McGill University, McIntyre Medical Sciences Building, 3655 Boulevard Sir William Osler, Montreal, Quebec, Canada, H3G 1Y6.
Ferguson
Andrew D
AD
Bergeron
John J M
JJ
Thomas
David Y
DY
D001483:Base Sequence; D017931:DNA Primers; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D005964:Glucosyltransferases / Q000737:chemistry / Q000378:metabolism*; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D017354:Point Mutation; D011487:Protein Conformation; D013379:Substrate Specificity
D017931:DNA Primers; D006023:Glycoproteins; D005964:Glucosyltransferases; C072423:mannosylglycoprotein 1,3-glucosyltransferase