Substrate specificity of the N-acetylglucosaminyl-phosphatidylinositol de-N-acetylase of glycosylphosphatidylinositol membrane anchor biosynthesis in African trypanosomes and human cells.
De-N-acetylation of N-acetylglucosaminyl-phosphatidylinositol (GlcNAc-PI) is the second step of glycosylphosphatidylinositol (GPI) membrane anchor biosynthesis in eukaryotes. This step is a prerequisite for the subsequent mannosylation of glucosaminyl-phosphatidylinositol (GlcN-PI) which leads to mature GPI membrane anchor precursors, which are transferred to certain proteins in the endoplasmic reticulum. The substrate specificities of the GlcNAc-PI de-N-acetylase activities of African trypanosomes and human (HeLa) cells were studied with respect to the N-acyl groups (R) that could be removed from a series of GlcNR-PI substrates, where R=acetyl (Ac), propionyl (Pr), butyryl (Bu), isobutyryl (iBu), pentanoyl (Pen) or hexanoyl (Hex). The data show that the trypanosomal and HeLa enzymes had similar specificities and that the turnover of GlcNR-PIs by the trypanosomal enzyme was in the order GlcNAc-PI>GlcNPr-PI>>GlcNBu - PI approximately GlcNiBu - PI approximately GlcNPen - PI>>GlcNHex - PI. The trypanosome and HeLa de-N-acetylases were unable to de-N-acetylate mannosylated GlcNAc-PI intermediates, which explains why de-N-acetylation must precede mannosylation in the GPI biosynthetic pathway.
Sharma
D K
DK
Department of Biochemistry, Carbohydrate Research Centre, University of Dundee, Scotland, U.K.
Smith
T K
TK
Crossman
A
A
Brimacombe
J S
JS
Ferguson
M A
MA
D000581:Amidohydrolases / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D002474:Cell-Free System; D017261:Glycosylphosphatidylinositols / Q000737:chemistry / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008358:Mannose / Q000378:metabolism; D051379:Mice; D051381:Rats; D013379:Substrate Specificity; D014346:Trypanosoma brucei brucei / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism
D017261:Glycosylphosphatidylinositols; D000581:Amidohydrolases; C087696:N-acetylglucosaminyl-phosphatidylinositol de-N-acetylase; D008358:Mannose