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Microbiology 155 (2009), 3281-3293; DOI  10.1099/mic.0.029975-0
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Microbiology 155 (2009), 3281-3293; DOI  10.1099/mic.0.029975-0
© 2009 Society for General Microbiology

Characterization of the Aspergillus fumigatus phosphomannose isomerase Pmi1 and its impact on cell wall synthesis and morphogenesis

Wenxia Fang, Xiaoying Yu, Bin Wang, Hui Zhou, Haomiao Ouyang, Jia Ming and Cheng Jin

Key Laboratory of Systematic Mycology and Lichenology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, PR China

Phosphomannose isomerase (PMI) is an enzyme catalysing the interconversion of mannose 6-phosphate (Man-6-P) and fructose 6-phosphate (Fru-6-P). The reaction catalysed by PMI is the first committed step in the synthesis of mannose-containing sugar chains and provides a link between glucose metabolism and mannosylation. In this study, the pmi1 gene was identified to encode PMI in the human fungal pathogen Aspergillus fumigatus. Characterization of A. fumigatus Pmi1 expressed in Escherichia coli revealed that this PMI mainly catalysed the conversion of Fru-6-P to Man-6-P and that its binding affinity for Man-6-P was similar to that of yeast PMIs, but different to those of PMIs from bacteria or animals. Loss of pmi1 was lethal unless Man was provided in the growth medium. However, a {Delta}pmi1 mutant cell showed a significantly reduced growth rate at a high concentration of Man. Biochemical analysis revealed that both inadequate and replete Man led to an accumulation of intracellular Man-6-P and a reduction in the amount of {alpha}-glucan in the cell wall. Uncoupling of the link between energy production and glycosylation by deletion of the pmi1 gene led to phenotypes such as defects in cell wall integrity, abnormal morphology and reduced conidiation. Our results reveal that PMI activity is essential for viability and plays a central regulatory role in both cell wall synthesis and energy production in A. fumigatus.

Correspondence
Cheng Jin
jinc{at}sun.im.ac.cn

Abbreviations: Fru-1,6-P, fructose 1,6-bisphosphate; Fru-6-P, fructose 6-phosphate; GDP-Man, GDP-mannose; Glc-6-P, glucose 6-phosphate; HPAEC-PAD, high-performance anion-exchange chromatography pulsed ampere detector; Man-1-P, mannose 1-phosphate; Man-6-P, mannose 6-phosphate; PMI, phosphomannose isomerase

The GenBank/EMBL/DDBJ accession number for the pmi1 gene sequence of Aspergillus fumigatus is AY700212.






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