Giardia lamblia: increased UDP-N-acetyl-D-glucosamine and N-acetyl-D-galactosamine transferase activities during encystation.
The cyst wall of Giardia lamblia is essential for survival of the parasite outside the host. N-acetyl-D-glucosamine (GalNAc) has been reported as a major terminal sugar of cyst wall glycoproteins and N-acetyl-D-galactosamine (GalNAc) as the major sugar of the fibrous insoluble cyst wall fraction. Therefore, we measured UDP-glycosyltransferase activities as the incorporation of [3H]UDP-sugar into an alcohol-insoluble product. We found that during encystation only UDP-GlcNAc and UDP-GalNAc transferase (UDP-GT) activities increased approximately three- to five-fold compared to nonencysting trophozoites. These activities were distributed approximately equally in the pellet and soluble fractions. The apparent K(m) and V(max) of UDP-GT in these fractions were similar. The activities from both fractions were dependent on Mn2+; however, the pellet enzymes were also partially activated by other metal ions. Both pUDP-GT and sUDP-GT were inhibited by uridine, UDP, and UDP sugars, but not by GlcNAc or GalNAc. Isolation and analysis of the reaction products suggest that pUDP-GT incorporate GlcNAc and GalNAc into glycoproteins, since the products were proteinase sensitive. In contrast, sUDP-GT products were resistant to proteinase treatment. Hydrolysis of the product of UDP-GlcNAc-T incorporation by trifluoroacetic acid released only glucosamine, while both glucosamine and galactosamine were released from UDP-GalNAc-T products, supporting the presence of an epimerase in Giardia which can convert GalNAc to GlcNAc during incorporation. This study suggests that at least two UDP-GT activities are induced during encystation, which are responsible for the transfer of GlcNAc and GalNAc from UDP-GlcNAc or UDP-GalNAc into both proteinase-sensitive and proteinase-resistant components of the Giardia cyst wall.
Das
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Department of Biological Sciences, University of Texas, El Paso 79968, USA. sdas@mail.utep.edu
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D000818:Animals; D002688:Chitinases / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003035:Cobalt / Q000494:pharmacology; D010450:Endopeptidases / Q000378:metabolism; D016829:Giardia lamblia / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D017350:N-Acetylgalactosaminyltransferases / Q000378:metabolism*; D017351:N-Acetylglucosaminyltransferases / Q000378:metabolism*; D009532:Nickel / Q000494:pharmacology; D015854:Up-Regulation; D014529:Uridine / Q000494:pharmacology; D014530:Uridine Diphosphate / Q000494:pharmacology; D014536:Uridine Diphosphate N-Acetylgalactosamine / Q000378:metabolism; D014537:Uridine Diphosphate N-Acetylglucosamine / Q000378:metabolism; D015032:Zinc / Q000494:pharmacology
D003035:Cobalt; D008345:Manganese; D014537:Uridine Diphosphate N-Acetylglucosamine; D014530:Uridine Diphosphate; D014536:Uridine Diphosphate N-Acetylgalactosamine; D009532:Nickel; D017350:N-Acetylgalactosaminyltransferases; D017351:N-Acetylglucosaminyltransferases; C023227:UDP-N-acetylglucosamine transferase; D002688:Chitinases; D010450:Endopeptidases; D008274:Magnesium; D015032:Zinc; D014529:Uridine