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

Abstract

Fungi contain several hexokinases, which are involved either in sugar phosphorylation or in carbon source sensing. Glucose and fructose phosphorylations appear to rely exclusively on glucokinase and hexokinase. Here, we characterized the catalytic glucokinase and hexokinase from the opportunistic human pathogen Aspergillus fumigatus and showed that both enzymes display different biochemical properties and play different roles during growth and development. Glucokinase efficiently activates glucose and mannose but activates fructose only to a minor extent. Hexokinase showed a high efficiency for fructose activation but also activated glucose and mannose. Transcript and activity determinations revealed high levels of glucokinase in resting conidia, whereas hexokinase was associated mainly with the mycelium. Consequentially, a glucokinase mutant showed delayed germination at low glucose concentrations, whereas colony growth was not overly affected. The deletion of hexokinase had only a minor impact on germination but reduced colony growth, especially on sugar-containing media. Transcript determinations from infected mouse lungs revealed the expression of both genes, indicating a contribution to virulence. Interestingly, a double-deletion mutant showed impaired growth not only on sugars but also on nonfermentable nutrients, and growth on gluconeogenic carbon sources was strongly suppressed in the presence of glucose. Furthermore, the glkA hxkA deletion affected cell wall integrity, implying that both enzymes contribute to the cell wall composition. Additionally, the absence of either enzyme deregulated carbon catabolite repression since mutants displayed an induction of isocitrate lyase activity during growth on glucose-ethanol medium. Therefore, both enzymes seem to be required for balancing carbon flux in A. fumigatus and are indispensable for growth under all nutritional conditions.

Hexokinase plays a critical role in deoxynivalenol (DON) production and fungal development in Fusarium graminearum

“…Fungi and plants contain several hexokinases known to be involved in signalling networks for the control of growth and development in response to the changing environment (Fleck and Brock, ; Moore et al ., ). Similar to the situation in Aspergillus spp.…”

Evolutionary Imprint of Catalytic Domains in Fungal PKS–NRPS Hybrids

“…Subsequently, the lovB downstream recombination flank (primers 07 and 08) could be cloned into NotI and Acc65I. The pyrithiamine resistance cassette was extracted from the pJET1 vector (kindly provided by the Brock group, HKI Jena, Germany)46 with NotI, which flanks both ends of the cassette. Insertion of the cassette into the NotI site of the LovB‐CheA(A‐T‐R) plasmid created the full recombination construct.…”

Protein kinase A and fungal virulence

“…The initial steps in glucose utilization are its uptake and activation to a sugar-phosphate. Recently, an A. fumigatus mutant deficient in the glucose phosphorylating enzymes, glucokinase and hexokinase, was shown to be hypersensitive to cell wall perturbation, which underscores the relationship between glucose utilization and the cell wall 130 . Furthermore, the Δ pkaC1 mutant of A. fumigatus displays increased sensitivity to both Congo red and SDS.…”