Genome Mining of Non-Conventional Yeasts: Search and Analysis of MAL Clusters and Proteins

Genomic clustering of functionally related genes is rare in yeasts and other eukaryotes with only few examples available. Here, we summarize our data on a nontelomeric MAL cluster of a non-conventional methylotrophic yeast Ogataea (Hansenula) polymorpha containing genes for alpha-glucosidase MAL1, alpha-glucoside permease MAL2 and two hypothetical transcriptional activators. Using genome mining, we detected MAL clusters of varied number, position and composition in many other maltose-assimilating non-conventional yeasts from different phylogenetic groups. The highest number of MAL clusters was detected in Lipomyces starkeyi while no MAL clusters were found in Schizosaccharomyces pombe and Blastobotrys adeninivorans. Phylograms of alpha-glucosidases and alpha-glucoside transporters of yeasts agreed with phylogenesis of the respective yeast species. Substrate specificity of unstudied alpha-glucosidases was predicted from protein sequence analysis. Specific activities of Scheffersomyces stipitis alpha-glucosidases MAL7, MAL8, and MAL9 heterologously expressed in Escherichia coli confirmed the correctness of the prediction-these proteins were verified promiscuous maltase-isomaltases. alpha-Glucosidases of earlier diverged yeasts L. starkeyi, B. adeninivorans and S. pombe showed sequence relatedness with alpha-glucosidases of filamentous fungi and bacilli.