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

Abstract

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