Mannoprotein

Sanjuan R., Zueco J., Stock R., Font de Mora J. Sentandreu R. (1995) Identification of glucan-mannoprotein complexes in the cell wall of Candida albicans using a monoclonal antibody that reacts with a (l,6)-/3-glucan epitope. Mzcroftzo/ogy, 141, 1545-1551. 

The cell wall of S. cerevisiae is composed of glucan, mannoproteins, and chitin (Klis, 1994 Cid et al., 1995). Of the mannoproteins, some of them are first synthesized as GPI-anchored and mannosylated proteins. Subsequently, they are incorporated from the plasma membrane to the cell wall and are covalently linked to the glucan there. Therefore, some signals should exist for dictating the cell wall incorporation. One found at a short N-terminal region near the GPI-attached asparagine (the co-site) is important (Hamada et al., 1998b). Namely, a plasma membrane GPI-anchored protein was localized to the cell wall if the (V/I)... 

A sensory study based on an incomplete factorial design allowed to demonstrate that astringency of procyanidins was reduced in the presence of rhamnogalaturonan II added at levels encountered in wine but was modified neither by anthocyanins nor by the other wine polysaccharides (mannoproteins and arabinogalactan proteins). Increase in ethanol level resulted in higher bitterness perception but had no effect on astringency. 

In the more abundant a chitin the chains in alternate sheets have opposite orientations,101102 possibly a result of hairpin folds in the strands. Native chitin exists as microfibrils of 7.25 nm diameter. These contain a 2.8-nm core consisting of 15-30 chitin chains surrounded by a sheath of 27-kDa protein subunits. The microfibrils pack in a hexagonal array, but the structure is not completely regular. Several proteins are present some of the glucosamine units of the polysaccharide are not acetylated and the chitin core is often calcified.103 The commercial product chitosan is a product of alkaline deacetylation of chitin but it also occurs naturally in some fungi.102 Chitin is also present in cell walls of yeasts and other fungi. It is covalently bonded to a P-l,3-linked glycan which may, in turn, be linked to a mannoprotein (see Section D,2)97... 

N-linked glycan is pictured in Fig. 4-17. Like many others, it has a number of sialic acid residues at the nonreducing ends and also contains N-acetyllactos-amine units. The major component of the cell walls of yeast (S. cerevisiae) is a mannoprotein that carries long N-linked oligosaccharides with highly branched outer chains of over 100 mannose residues170 (see also Section C,3). 

Mannoprotein of yeast cell walls 185 Mannose (Man) 161s, 163s Mannose-6-phosphate 185 Mannose-6-phosphate isomerase 693 MAP kinase cascade 576-578 figure 579... 

The cell wall of the yeast Saccharomyces is rich in mannoproteins that contain 50-90% mannose.264 The 250-residue mannan chains consist of an a-1,6-linked backbone with mono-, di-, and tri-mannosyl branches. These are attached to the same core structure as that of mammalian oligosaccharides. All of the core structures are formed in a similar way.258 265 The mannoproteins may serve as a "filler" to occupy spaces in a cell wall constructed from P-1,3- and P-l,6-linked gly-cans and chitin. All of the four components, including the mannoproteins, are covalently linked together.266 As was emphasized in Chapter 4 (pp. 186-188)... 

The study of the biosynthesis of D-mannoproteins in other fungi is less developed. It has already been mentioned that the participation of Man-P-Dol as the glycosyl donor in O-glycosylation was demonstrated in Neuro-spora crassa97 and in Fusarium solani f. pisi.56 In the latter, the lipid acceptor was identified as C90- to C110-dolichols. In Hansenula species, O-glycosyla-tion follows the same pathway that is D-mannose linked to L-serine or L-threonine is incorporated by way of Man-P-Dol, and further elongation... 

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. 

It can precipitate as potassium hydrogen tartrate (KHT) or as calcium tartrate (CaT), the latter being practically insoluble in aqueous solutions. Their equilibrium solubility varies with temperature, pH, and alcohol content, while the presence of a few wine components, such as polysaccharides and mannoproteins, may hinder spontaneous nucleation even if the solution is supersaturated. From Figure 14 that shows the equilibrium tartaric acid-dissociated fractions versus pH and ethanol volumetric fraction (Berta, 1993 Usseglio-Tomasset and Bosia, 1978), it can be seen that in the typical pH range (3 4) of wines KHT is predominant. As temperature is reduced from 20 to 0°C, KHT solubility in water or in a 12% (v/v) hydro-alcoholic solution reduces from 5.11 to 2.45 kg/m3 or from 2.75 to 1.1 kg/m3, respectively (Berta, 1993). Each of these data also varies with pH and reaches a minimum at the pH value associated with the maximum concentration of the hydrogen tartrate anions. For the above-mentioned solutions, the solubility minimum shifts from pH 3.57 to pH 3.73 as the ethanol content increases from 0 to 12% (v/v) (Berta, 1993). 

N. P. Arbatsky, V. N. Shibaev, and N. K. Kochetkov, A new approach to localization of the O-glycosylation sites in glycoproteins Mass-spectrometric analysis of O-glycopeptides formed upon the reductive cleavage of the yeast mannoprotein by LiBH4-LiOH, Doklady Chem., 387 (2002) 328-331. 

Cohen, R. E., Zhnag, W., and Ballou, C. E. (1982). Effects of mannoproteins in Saccharomyces cerevisiae core oligosaccharide structure. J. Biol. Chem., 257, 5730-5737. 

Fibrous Glucan Entrapped Mannoprotein Chitin GPI Anchor Plasma Membrane... 

Calderone RA, Wadsworth E Characterization of mannoproteins from a virulent Candida albicans strain and its derived, avimlent strain. Rev Infect Dis 1988 10 S423-S427. 

It has been shown recently that mannoproteins from yeast cell walls make a significant contribution to improving foaming properties (Nunez et al. 2006). These authors also demonstrated the importance of the method of mannoprotein extraction from the yeast cell wall, since not all mannoproteins have the same effect on the foam of sparkling wines. 

Yeast autolysis could be defined as the hydrolysis of biopolymers under the action of hydrolytic enzymes which releases cytoplasmic (peptides, amino acids, fatty acids and nucleotides) and cell wall (glucans, mannoproteins) compounds into the wine (Alexandre et al. 2006).Usually, autolysis takes place at the end... 

Caridi, A. (2006). Enological functions of parietal yeast mannoproteins. Antonie Van Leeuwenhoek, 89, 417-A22. 

---