Biosynthesis yeast mannoprotein

In this paper I intend to summarize what we know about yeast mannoprotein structure, what features of the biosynthetic pathway have been defined, how genetic techniques have been useful in gaining this information, and what is known about the genetic control of mannoprotein biosynthesis. 

The biosynthesis in yeast of two enzymes that are D-mannoproteins has been studied. A membrane-associated isozyme of invertase (EC 3.2.1.26) has been shown to be a precursor of the external invertase.190 Its molecular weight, as determined by SDS-poly(acrylamide) gel electrophoresis, is 50,000, that is, smaller than that of the external invertase, and it correlates well with the presence of only the inner-core sugars of the final form. It is strictly bound to membranes, possibly those of the endoplasmic reticulum, and it can be completely split191 by endo-/3-N-acetylglucosaminidase H (EC 3.2.1.30). The addition of tunicamycin, which specifically inhibits formation of d-GIcNAc-PP-DoI, inhibits synthesis of external invertase, as well as further formation of the membrane-associated form, which completely disappears after addition of the antibiotic.190 In these aspects, the synthesis of this extracellular enzyme follows the pathway for secreted glycoproteins in animal systems. 

Carboxypeptidases.—A study of the biosynthesis of yeast carboxypeptidase Y (a mannoprotein) has revealed that a membrane fraction contains a precursor of the enzyme, which, although it has a higher molecular weight than the enzyme, is not a complex of the enzyme and its specific inhibitor. ... 

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