-Glycoproteomic Characterization of Mannosidase and Xylosyltransferase Mutant Strains of .

At present, only little is known about the enzymatic machinery required for -glycosylation in , leading to the formation of -glycans harboring Xyl and methylated Man. This machinery possesses new enzymatic features, as -glycans are independent of β1,2--acetylglucosaminyltransferase I. Here we have performed comparative -glycoproteomic analyses of insertional mutants of mannosidase 1A (IM ) and xylosyltransferase 1A (IM ). The disruption of affected methylation of Man and the addition of terminal Xyl. The absence of XylT1A led to shorter -glycans compared to the wild type. The use of a IM xIM double mutant revealed that the absence of Man1A suppressed the IM phenotype, indicating that the increased -glycan trimming is regulated by core β1,2-Xyl and is dependent on Man1A activity. These data point toward an enzymatic cascade in the -glycosylation pathway of with interlinked roles of Man1A and XylT1A. The results described herein represent the first step toward a functional characterization of the enzymatic -glycosylation machinery in .