Glucose metabolism in Neurospora is altered by heat shock and by disruption of HSP30

We compared the metabolism of 1-13C]glucose by wild type cells of Neurospora crassa at normal growth temperature and at heat shock temperatures, using nuclear magnetic resonance analysis of cell extracts. High temperature led to increased incorporation of 13C into trehalose, relative to all other metabolites, and there was undetectable synthesis of glycerol, which was a prominent metabolite of glucose at normal temperature (30 degrees C). Heat shock strongly reduced formation of tricarboxylic acid cycle intermediates, approximately 10-fold, and mannitol synthesis was severely depressed at 46 degrees C, but only moderately reduced at 45 degrees C. A mutant strain of N. crassa that lacks the small alpha-crystallin-related heat shock protein, Hsp30, shows poor survival during heat shock on a nutrient medium with restricted glucose. An analysis of glucose metabolism of this strain showed that, unlike the wild type strain, Hsp30-deficient cells may accumulate unphosphorylated glucose at high temperature. This suggestion that glucose-phosphorylating hexokinase activity might be depressed in mutant cells led us to compare hexokinase activity in the two strains at high temperature. Hexokinase was reduced more than 35% in the mutant cell extracts, relative to wild type extracts. alpha-Crystallin and an Hsp30-enriched preparation protected purified hexokinase from thermal inactivation in vitro, supporting the proposal that Hsp30 may directly stabilize hexokinase in vivo during heat shock.