| Definition: |
Any glycoprotein containing ca. 15-90 wt% mannose. There are four basic types, assigned by their structure, location, and function. In the cell wall, intermeshed with the glucan network, is a structural mannoprotein containing up to 90% mannose. In the periplasm of the cell are mannoprotein enzymes (e.g.invertase and acid phosphatase), containing ca. 50% mannose. Inside the cell, 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 di-N-acetylchitobiose units linked to asparagine. The fourth type, represented by the sexual agglutinin carried on the surface of Hansenula wingei 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.
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