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

Functional diversification of the duplicated genes LkLEU4 and LkLEU4BIS from Lachancea kluyveri resulted in different transcriptional regulation and predicted subcellular localization of the isozymes but similar kinetic properties. The first committed step in the leucine biosynthetic pathway is catalyzed by alpha-isopropylmalate synthase (alpha-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 SAKL0F05170 g (LkLEU4BIS) paralogous genes, which are homologous to other yeast alpha-IPMS sequences. Here, we investigate whether these paralogous genes encode functional alpha-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 alpha-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.

Automated summary

The duplicated genes LkLEU4 and LkLEU4BIS from Lachancea kluyveri have undergone functional diversification, resulting in different transcriptional regulation and predicted subcellular localization, but similar kinetic properties. These genes play important roles in leucine biosynthesis, and their functional diversification is achieved through differential transcription regulation and subcellular localization.