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

Abstract

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 Dpmi1 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 a-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.

Mapmi gene contributes to stress tolerance and virulence of the entomopathogenic fungus, Metarhizium acridum

“…Mannose is involved also in the synthesis of the protective capsule and other structures within fungal cells (Bose et al, 2003;Fang et al, 2009;Pitkänen et al, 2004;Wills et al, 2001). GDP-mannose, a nucleotide sugar described by Cabib and Leloir (1954), has been demonstrated to be the activated donor of mannose for biosynthesis of mannose-containing glycoconjugates (Wills et al, 2001).…”

“…Pmi genes have been identified and characterized in some fungi Fang et al, 2009;Smith et al, 1992;Smith and Payton, 1994;Wells et al, 1993;Wills et al, 2001). Growth was inactivated in a pmi deletion mutant but restored by adding mannose to the medium (Fang et al, 2009;Payton et al, 1991). However, excess exogenous mannose was toxicy to the pmi-deletion mutant due to the accumulation of intracellular Man-6-P, which inhibited further growth (Fang et al, 2009;Pitkänen et al, 2004).…”

“…Exogenous mannose could also be utilized to form mannose 6-phosphate through the action of hexokinase (HK) (Derossi et al, 2006;Lochlainn and Caffrey, 2009). Pmi genes have been identified and characterized in some fungi Fang et al, 2009;Smith et al, 1992;Smith and Payton, 1994;Wells et al, 1993;Wills et al, 2001). Growth was inactivated in a pmi deletion mutant but restored by adding mannose to the medium (Fang et al, 2009;Payton et al, 1991).…”

Regulatory Circuitry Governing Fungal Development, Drug Resistance, and Disease

“…Furthermore, the corresponding mutant is defective in polarity maintenance and branching-site selection and produces hyperbranched hyphal cells (253). Other proteins involved in the processing of mannose, including the phosphomannose isomerase (PMI) protein Pmi1, have also been implicated in A. fumigatus morphogenesis (175).…”

Aspergillus fumigatus Catalytic Glucokinase and Hexokinase: Expression Analysis and Importance for Germination, Growth, and Conidiation

“…Both GlkA and, especially, HxkA were shown to be present in ethanol-grown mycelia, supporting the idea of sugar phosphorylation from storage compounds. In addition, aside from the importance in the production of mannose-6-phosphate for mannoproteins (13), large amounts of glucose are also required for chitin production. Therefore, it can be assumed that gluconeogenesis not only provides glucose-6-phosphate, which is directly consumed for biosynthetic purposes, but also produces glucose, which can be used when needed.…”