Biosynthesis, cellulase

Three regulators were identified by genetic analysis. The main repressor, KdgR, controls the transcription of pectinase genes, the intracellular catabolic pathway and the secretion machinery. The PecS repressor controls the production of pectate lyases and cellulases, the secretion machinery and the biosynthesis of a blue pigment. PecT acts as a repressor of the production of some pectate lyases. Other proteins are involved in the regulation of pectinase s5mthesis but their role is not well characterized. 

However, pyrimethanil and mepanipyrim do not inhibit proteinase, cellulase or polygalacturnase activity in Botrytis cinerea17 but reduce pectinase and invertase secretion with an associated increase in their intracellular accumulation. This is proposed to be the mechanism of action of the anilinopyrimidines but the biochemical basis of the effect is not known. There is evidence that suggests the involvement of methionine biosynthesis inhibition.18... 

The fact that transglycosylation products of one of the enzymic components of the cellulase system of T. reesei can stimulate the production of the system may be of great importance in elucidating the mechanisms of the processes involved in the biosynthesis of these enzymes. Sophorose may be an early transglycosylation product, whose... 

Biosynthesis, Purification, and Mode of Action of Cellulases of Trichoderma reesei... 

Tt is a widely recognized fact that true cellulolytic microorganisms A produce three basic cellulase components IS), and that these enzyme components act in concert to hydrolyze crystalline cellulose to glucose (6). Many research laboratories have undertaken the task to purify cellulose components from various cellulolytic microorganisms and to study the mechanisms of cellulose hydrolysis. Much information has accumulated concerning the mode of action of cellulose hydrolysis since Reese et al. first proposed the Ci-C concept (7). In spite of this, however, conflicting reports still flourish concerning the composition of the "cellulase complex, the multiplicity of cellulase components, the biosynthesis of cellulose, and the mechanisms of cellulose hydrolysis. 

The multiplicity of cellulases is of fundamental interest because of its implications on the basic understanding of cellulose hydrolysis as well as the regulation of cellulase biosynthesis. 

While cellobiose is a poor inducer, lactose, the milk sugar, is a good inducer of cellulase biosynthesis. Lactose-induced fungus produces a cellulase complex which is identical to those cellulases induced by cellulose (for SDS gels see Figure 9b, e, h, i). 

Cellobiose, a dimer of /3-1,4-linked glucose, is reported to be a cellulase inducer in T. reesei as well as in several other fungi (20,28,33, 34). But whether cellobiose is a true inducer is questionable since Reese et al. (35) reported that cellobiose could induce as well as inhibit cellulase biosynthesis. The same is also true for glucose. Whether glucose or cellobiose is an inducer or inhibitor depends on the concentration of sugars in the environment. 

Cellulose is a universal inducer of cellulase biosynthesis. Since cellulose is insoluble, the microorganisms are unable to utilize it unless it has been hydrolyzed first to glucose or soluble oligomers of cellulose. But if cellulose cannot be utilized directly without first being solubilized, the question arises as to how it gets into the cells to act as an inducer. There appear to be several possible explanations. 

Table VI. Growth and Cellulase Biosynthesis After Media Shifting0...

T. reesei is a useful experimental organism for studying regulation of extracellular protein biosynthesis. When grown in a medium in which an exogeneous inducer serves as the major or sole carbon source, T. reesei, synthesizes and secretes a cellololytic enzyme into the medium. Similarly, the extracellular cellulase is produced upon limitation of the carbon source and limitation of the utilization of the carbon source (31). Presently, there appears to be little data in the literature concerning regulation of cellulase biosynthesis. 

Montenecourt and Eveleigh (37), using a special agar screening technique, have also isolated a cellulase enhanced mutant (NG-14). They suggest, however, that the cellobiohydrolase and the endoglucanase biosynthesis are regulated by different controls. They base this assumption on data for the relative ratios of cellulases obtained from this mutant needed to hydrolyze different substrates. 

More experiments are needed before any conclusions can be made. It appears that the isolation and study of a mutant which synthesizes only one cellulolytic enzyme component is needed if headway is to be made on determining the nature of regulatory control of cellulase biosynthesis. 

The formation of plant cellulases has been found to be closely regulated by different growth hormones, particularly auxin (6,11), steroids (12), or ethylene gas (13). The hormones act in different tissues under different circumstances, and they seldom lead to such high cellulase activity that there is a net decline in total cellulose. Indeed, cellulose biosynthesis usually continues even while partial hydrolysis occurs, and net cellulose deposition often keeps pace with growth under all of these conditions (14). 

Our present knowledge of the mechanism of biosynthesis of the two pea cellulases may be summarized diagrammatically as follows, where the organelles involved are indicated in bold type, the processes required are in parentheses, and the physical transfer of template, intermediates, or products is designated by arrows. 

Although several properties of each of the three proteins have been investigated, most of our work has been done with the C form because (a) it has the highest affinity for crystalline cellulose (b) it is the predominant form in most, but not aU, T. viride cellulase preparations (c) it contains more carbohydrate than the A and B forms, suggesting that they may be degradation products from or intermediates in the biosynthesis of hydrocellulase C and (d) it forms a slightly more active hydrocellulase system when recombined with the enzymes of fraction I. 

Gong C-S, Ladisch MR, Tsao GT (1977) Cellobiase from Trichoderma viride-. purification, properties,kinetics, and mechanism. Biotechnology and Bioengineering 19 959-981 Gong C-S, Ladisch MR, Tsao GT (1979) Biosynthesis, purification and mode of action of cellulase of Trichoderma reesei-. hydrolysis of cellulose mechanisms of enzymatic and acid catalysis. Advances in Chemistry Series vol. 181, American Chemical Society, Washington, DC, pp 261-287... 

Li C, Yoshimoto M, Fukunaga K et al. (2007) Characterizarion and immobihzation of hposome-bound cellulase for hydrolysis of insoluble cellulose. Biores Technol 98(7) 1366-1372 Liu W, Wang P (2007) Cofactor regeneration for sustainable biosynthesis. Biotechnol Adv 25 369-384... 

Ryu DDY, Mandels M. (1980). Cellulases biosynthesis and applications. Enzyme Microb Technol, 2, 91-102. 

Continuous culture studies for the production of cellulase have been carried out growing Trichoderma viride on a medium containing commercial D-glucose as the carbon source. Some data on cellulase biosynthesis were examined and correlated in terms of a maturation time model. Specific oxygen uptake rates were correlated with specific production rates. Mutant strains not producing cellulases have been induced and isolated from Trichoderma viride. Enrichment of the mutants was carried out by nystatin selection. 

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