Manno-proteins

The main structural constituents of Saccharomyces cerevisiae yeast cell wall are glucans and mannans with a minor proportion of chitin (Walker 1998). Manno-proteins are located in the outer layer of the yeast cell wall and determine most of the surface properties of the wall. Vasserot et al. (1997) studied the capacity of yeast lees to adsorb anthocyanins in an attempt to reduce the detrimental effects of charcoal on the color of red musts and wines. Experiments based on model wine solutions revealed that yeast lees possess a greater affinity for anthocyanins than... 

However, metatartaric acid is hydrolyzed in wine, and loses its effectiveness, while adding tartaric acid may even facilitate potassium bitartrate crystallization. Under the same conditions, manno-proteins are stable and have a durable protective effect on tartrate crystallization. To demonstrate this difference, white wines treated with metatartaric acid or Mannostab and kept at 30°C for 10 weeks were then subjected to a cold test. Crystallization occurred in the sample treated with metatartaric acid, while the Mannostab sample remained stable (Table 1.22). 

CMCs are also reputed to promote solubilization of proteins and stabilize solutions containing them (Federson and Thorp, 1993). This property is useful in winemaking for the purpose of preventing protein casse. These CMC-protein interactions may be compared to the carbohydrate-protein association in glycoproteins and yeast manno-proteins. 

It should also be noted that the purified manno-protein preparation obtained by digesting yeast cell walls contains another protein fraction that has a protective effect on tartrate precipitation (Moine-Ledoux et al., 1997) (Section 1.7.7). It is perfectly possible to envisage using an industrial preparation of this protective colloid in the near future to stabilize white wines and prevent tartrate precipitation. 

Once the structure of mannan was established to be manno-protein(s) we studied its biosynthesis by following the formation of both the peptide and carbohydrate moieties. In these studies one of the most powerful techniques is the dissection of a metabolic route by inhibiting specific reactions with antimetabolites. In the case of mannoproteins the two moieties are quite different and are polymerized by different biosynthetic routes. We inhibited protein formation with the antibiotic cycloheximide which freezes translation of the genetic message at the level of polysomes. 

Recent studies carried out in our laboratory suggest that the mRNA for the manno-protein might have a longer half-life than the average mRNA for cellular proteins. On the other hand, inhibition of protein synthesis with cycloheximide does not interfere with glucan formation indicating that glucan synthetase(s) show a slow turnover. 

Kaukonen K, Savolainen J, Viander M et al (1993) Characterization of Aspergillus umbrosus carbohydrate antigens by biotinylated lectins and IgG response to mannan/manno-protein antigens in patients with farmer s lung. Clin Exp Allergy 23 21-27... 

Polysaccharide-protein A. calcoaceticus strains Manno-protein... 

Concanavalin A is an antibody-like protein isolated from the jack bean. 82 It was shown to form a precipitate with glycogen and with yeast mannan, and was later also used to differentiate between glycogen-like polysaccharides from various sources.283 284 It has now been shown that concanavalin A forms a precipitate only with branched polysaccharides which contain terminal, nonreducing a-D-glucopyranosyl or a-D-manno-pyranosyl groups.18 The combining sites of the protein appear to be directed against the 2-deoxy-a-D-aratano-hexopyranosyl system.2 ... 

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