Mannan protein complex

A historical review of the development of our knowledge of the yeast cell wall was given by Phaff (I). Most information based on chemical studies has been derived, by far, from studies with cell walls from baker s yeast, Saccharomyces cerevisiae, and closely related species. The principal components of Saccharomyces walls are several types of glucan and a mannan-protein complex which may contain variable proportions of phosphate. A low content of chitin (ca. 1% ) may be present depending on the number of times a cell has produced buds. The reason for this is that chitin is present only in the bud scars (ca. 3 pm2 in area) produced on the surface of a mother cell (2), each at a different place on the cell surface. 

A glycoprotein which has been isolated from the cell walls of baker s yeast was shown to be a D-mannan-protein complex. After immobilization by covalent attachment to macroporous agarose, this was used in the purification of an a-D-mannosidase from jack-bean meal. 

Yeasts are single-cell fungi with cell walls consisting of two interlocking structures, either of which is sufficient to keep the characteristic shape. One structure is made entirely of glucan (a poly-anhydride of glucose), and the other is a mannan—protein complex bound to disulfide linkages. Only when both structures are broken is the cytoplasm extruded (Bacon etaL, 1965). 

Micrococcus lysodeikticus cells (lysozyme lysate) D-Mannan-protein complex Saccharomyces cerevisiae) Modulator protein (rabbit skeletal muscle)... 

A polysaccharide-protein complex isolated from the cell walls of Torulopsis Candida contains residues of D-mannose and 2-acetamido-2-deoxy-D-glucose. The D-mannose units are attached singly and as (1 - 2)-linked di- and trisaccharides to L-serine residues of the peptide chain by 0-glycosidic linkages, while D-mannan chains are terminated at the reducing end by units of chito-biose which in turn are attached to the peptide backbone by A -glycosidic linkages. 

Biosorption is a rather complex process affected by several factors that include different binding mechanisms (Figure 10.4). Most of the functional groups responsible for metal binding are found in cell walls and include carboxyl, hydroxyl, sulfate, sulfhydryl, phosphate, amino, amide, imine, and imidazol moieties.4 90 The cell wall of plant biomass has proteins, lipids, carbohydrate polymers (cellulose, xylane, mannan, etc.), and inorganic ions of Ca(II), Mg(II), and so on. The carboxylic and phosphate groups in the cell wall are the main acidic functional groups that affect directly the adsorption capacity of the biomass.101... 

In terms of quantity, probably cellulose (O Chap. 6.3) is the most important plant polysaccharide and has a key role in maintaining the cell wall. Enz)me complexes, with perhaps 36 subunits, produce this polymer and a number of the relevant CESA (cellulose synthase) genes have been identified defects in some CESA genes are associated with some irx (irregular xylem) phenot) es [323]. Related proteins, encoded by cellulose synthase-like A(CslA) genes, are apparently /3-mannan synthases [324]. Mannans are only one of the many hemicellu-... 

Proteins of a crude enzyme preparation obtained from the cultivation medium of the basidiomycete Phellinus abietis were separated by gel filtration and ion-exchange chromatography. The preparation contained a minimum of three enzymes capable of splitting a-D-mannosidic bonds a-D-mannosidase, exo-D-mannanase, and e/ido-D-mannanase, which were separated. Some properties of the D-mannanase complex of the crude enzyme preparation, and of a partially purified a-D-mannosidase, were examined. The D-mannanase complex exhibited two pH optima, its temperature optimum being 45 C. The pH optimum of purified a-D-mannosidase was at pH 5.0, the temperature optimum was at 60 °C the enzyme had a relatively high heat stability. The of a-D-mannosidase for 4-nitrophenyl a-D-mannopyranoside was 1.5xl0 M. Pure a-D-mannosidase did not split D-mannan. 

The best characterized component of the cell wall is the a-mannan [36] (Fig. 16.3). The molecule is made up of an inner core of a repeating a-(l-6) chain of mannose residues with short side chains of a-(l-2) and a-(l-3) linked residues. At the end of this inner core are two A-acetyl glucosamine residues (chitobiose) and the terminal one is attached to the carboxylic acid residue in the side chain of an aspartic acid residue of a protein. Attached to the opposite end of the inner core molecule is an outer chain of 100-150 mannose residues. This unit consists of an a(l-6) backbone with a(l-2) and a(l-3) side chains, some of which contain phosphodiester linkages. In addition to this complex molecule, and attached to the same protein via serine and threonine hydroxyl groups, are short a(l-2) and a(l-3) chains of mannose residues. Other observations on the structure of the wall reveal that glucan is also covalently... 

Inhibition by 2-deoxy-D-arai>mn-hexose of the biosynthesis of the cell-wall mannan in Saccharomyces cerevisiae appears to involve a complex mechanism that disrupts the synthesis of protein rather than glycosylation. Studies using a particulate enzyme from Mycobacterium smegmatis have demonstrated that polyisoprenyl D-mannosyl phosphates are obligatory donors, while preparations obtained from Hansenula holstii have shown that a D-mannosyl-lipid is involved in the synthesis of mannosylated serine (or threonine) residues. ... 

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