Cell wall synthesis and central carbohydrate metabolism are interconnected by the SNF1/Mig1 pathway in Kluyveromyces lactis.

The trimeric AMP-activated kinase complex (AMPK) is conserved from yeast to humans and is best known for its role in balancing energy metabolism. Additional functions, including the regulation of cell wall biosynthesis, have been proposed for the SNF1 complex, the baker's yeast homolog of AMPK. We here demonstrate that this function is conserved in the Crabtree-negative milk yeast Kluyveromyces lactis. Deletion mutants in the genes encoding the subunits of the trimeric complex (Klsnf1, Klgal83, Klsnf4) displayed increased sensitivities towards cell wall stress agents and a mutant lacking the kinase subunit had a thinner cell wall in transmission electron micrographs as compared to wild type. Epistasis analyses demonstrated that the KlSNF1 complex acts in parallel to cell wall integrity (CWI) signaling and stress sensitivities of Klsnf1 deletions can be suppressed by additional deletions in glycolytic genes (KlPFK1, KlPFK2, KlPGI1) or by a Klmig1 mutant. Western blot analyses of an HA-tagged KlMig1p revealed its phosphorylation on ethanol medium similar to its S. cerevisiae ortholog, but a substantial amount of protein remained phosphorylated even with high glucose concentrations. Application of cell wall stress shifted this equilibrium towards the non-phosphorylated fraction of KlMig1p. We conclude that KlMig1p may exert a negative regulatory function on cell wall biosynthesis.