HEXOSAMINE AND CELL-WALL BIOGENESIS IN THE AQUATIC FUNGUS BLASTOCLADIELLA-EMERSONII

被引:19
作者
MAIA, JCD
机构
[1] Departamento de Bioquimica, Instituto de Quimica, Universidade de Sao Paulo, 01498-970 Sao Paulo
关键词
HEXOSAMINE; BIOSYNTHESIS; CHITIN; AMIDOTRANSFERASE; PROTEIN PHOSPHORYLATION;
D O I
10.1096/fasebj.8.11.8070634
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Chitin, a beta-(1-->4) polymer of N-acetylglucosamine, is an important constituent of fungal cell walls. This polymer is synthesized by the incorporation of N-acetyl-D-glucosamine units from the precursor UDP-N-acetyl-D-glucosamine (UDP-GlcNAc) in a reaction catalyzed by chitin synthase. In the aquatic fungus Blastocladiella emersonii, chitin, the major component of the cell wall, is synthesized and incorporated in the cell surface of the free-swimming zoospore during the abrupt transition from this wall-less cell to the sessile, wall-containing cyst. Studies with cycloheximide indicate that chitin synthesis occurs in the apparent absence of protein synthesis, and thus posttranslational controls presumably regulate the cell wall biogenesis during encystment. Glutamine: fructose 6-phosphate amidotransferase, first enzyme of the hexosamine biosynthetic pathway, was found to play a central role in the regulation of chitin synthesis in this fungus. This enzyme exists in two forms, which are interconvertible by phosphorylation or dephosphorylation of serine residues. It is allosterically inhibited in the phosphorylated form, as it is in the zoospore, by UDP-GlcNAc. In addition, UDP-GlcNAc inhibits the dephosphorylation of amidotransferase catalyzed by protein phosphatases 2A and 2C. Thus, UDP-GlcNAc plays a dual role in hexosamine and chitin synthesis in zoospore: it not only inhibits the phosphorylated form of the enzyme but also prevents its dephosphorylation. The available data suggest that substrate availability plays a role in the control of chitin synthesis during zoospore differentiation.
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页码:848 / 853
页数:6
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