Identification and analysis of a Class 2 α-mannosidase from Aspergillus nidulans

A Class 2 alpha-mannosidase gene was cloned and sequenced from the filamentous fungus Aspergillus nidulans. A portion of the gene was amplified using degenerate oligonucleotide primers which were designed based on similarity between the Saccharomyces cerevisiae vacuolar and rat ER/cytosolic Class 2 protein sequences, The PCR amplification product was used to isolate the full length gene, and DNA sequencing revealed a 3383 bp coding region containing three introns. The predicted 1049 amino acid reading frame contained six potential N-glycosylation sites and encoded a protein of 118 kDa, The protein sequence did not appear to encode a typical fungal signal sequence or membrane spanning domain, Although the cellular location of the A.nidulans mannosidase was not determined, experimental evidence suggested that it was located within a subcellular organelle. The Matchbox sequence similarity matrix indicated that the A.nidulans protein sequence was more highly similar to the rat ER/cytosolic (Rij = 0.33) and S.cerevisiae vacuolar alpha-mannosidases (Rij = 0.43) than tbe rat and yeast sequences were to each other (Rij = 0.29), These three enzymes were found to be distantly related to other Class 2 sequences, and compose a third subgroup of Class 2 alpha-mannosidases, as shown by ClustalW sequence alignment.