Two alpha isopropylmalate synthase isozymes with similar kinetic properties are extant in the yeast Lachancea kluyveri.

Abstract

The first committed step in the leucine biosynthetic pathway is catalyzed by α-isopropylmalate synthase (α-IPMS, EC 2.3.3.13), which in the Saccaromycotina subphylum of Ascomycete yeasts is frequently encoded by duplicated genes. Following a gene duplication event, the two copies may be preserved presumably because the encoded proteins diverge in either functional properties and/or cellular localization. The genome of the petite-negative budding yeast Lachancea kluyveri includes two SAKL0E10472 (LkLEU4) and SAKL0F05170g (LkLEU4BIS) paralogous genes, which are homologous to other yeast α-IPMS sequences. Here, we investigate whether these paralogous genes encode functional α-IPMS isozymes and whether their functions have diverged. Molecular phylogeny suggested that the LkLeu4 isozyme is located in the mitochondria and LkLeu4BIS in the cytosol. Comparison of growth rates, leucine intracellular pools and mRNA levels, indicate that the LkLeu4 isozyme is the predominant α-IPMS enzyme during growth on glucose as carbon source. Determination of the kinetic parameters indicates that the isozymes have similar affinities for the substrates and for the feedback inhibitor leucine. Thus, the diversification of the physiological roles of the genes LkLEU4 and LkLEU4BIS involves preferential transcription of the LkLEU4 gene during growth on glucose and different subcellular localization, although ligand interactions have not diverged.