mannoprotein
mannoprotein
Any glycoprotein containing ca. 15-90 wt% mannose. There are four basic types, assigned by their structure, location, and function. <em>In the cell wall</em>, intermeshed with the glucan network, is a structural mannoprotein containing up to 90% mannose. <em>In the periplasm of the cell</em> are mannoprotein enzymes (e.g.invertase and acid phosphatase), containing ca. 50% mannose. <em>Inside the cell</em>, predominantly in the vacuole, are hydrolytic enzymes, e.g. carboxypeptidase, containing ca. 15% mannose. In each of these three types, most of the carbohydrate is attached to the protein by <em>di</em>-<em>N</em>-acetylchitobiose units linked to asparagine. <em>The fourth type</em>, represented by the sexual agglutinin carried on the surface of <em>Hansenula wingei</em> and other strongly agglutinative yeasts, contains about 85% mannose, mostly linked to Ser and Thr residues in the protein. Ca. 10% of the mannose in the periplasmic and cell wall mannoproteins is linked to protein in a similar manner, in which the carbohydrate portion consists of a mannose polymer.