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A super-secondary structure predicted to be common to several alpha-1,4-D-glucan-cleaving enzymes.

ABSTRACT: Predictions of protein secondary structure are used with amino acid sequence alignments to show that the N-terminal domains of cyclodextrin glucanotransferases and a yeast alpha-glucosidase may have the same super-secondary structure as alpha-amylases, i.e. an (alpha/beta)8-barrel fold. Sequence similarities provide evidence that glucanotransferases, and possibly the glucosidase, are, like alpha-amylases, Ca2+-containing enzymes. The relationship between substrate specificity and the nature of the amino acid residues proposed at the active site is discussed for the transferases and alpha-glucosidase. A set of three programs for an Apple IIe computer to carry out the calculations described by Garnier, Osguthorpe & Robson [(1978) J. Mol. Biol. 120, 97-120] and a set of four programs for an Apple IIe computer to carry out the calculations described by Levin, Robson & Garnier [(1986) FEBS Lett. 205, 303-308] have been deposited as Supplementary Publication SUP 50149 (25 pages) at the British Library Document Supply Centre, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1989) 257, 5.

SUBMITTER: MacGregor EA

PROVIDER: S-EPMC1138484 | biostudies-other | 1989 Apr

REPOSITORIES: biostudies-other

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Super-secondary structure peptidomimetics: design and synthesis of an α-α hairpin analogue.

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Project description:The food enzyme glucan 1,4-α-maltotetraohydrolase (4-α-d-glucan maltotetraohydrolase, EC 3.2.1.60) is produced with a genetically modified Bacillus licheniformis strain DP-Dzr46 by Danisco US Inc. The genetic modifications do not give rise to safety concerns. The food enzyme is free from viable cells of the production organism and recombinant DNA. The glucan 1,4-α-maltotetraohydrolase food enzyme is intended to be used in baking processes. Based on the maximum use levels, dietary exposure to the food enzyme-Total Organic Solids (TOS) was estimated to be up to 0.405 mg TOS/kg body weight (bw) per day in European populations. The toxicity studies were carried out with another glucan 1,4-α-maltotetraohydrolase from B. licheniformis (strain DP-Dzf24). The Panel considered this food enzyme as a suitable substitute to be used in the toxicological studies, because it derives from the same recipient strain as strain DP-Dzr46, the location of the inserts is comparable, no partial inserts were present and the production methods are comparable. Genotoxicity tests did not raise a safety concern. The systemic toxicity was assessed by means of a repeated dose 90-day oral toxicity study in rats. The Panel identified a no observed adverse effect level (NOAEL) at the highest dose of 94 mg TOS/kg bw per day that, compared with the estimated dietary exposure, results in a sufficiently high margin of exposure of at least 232. Similarity of the amino acid sequence to those of known allergens was searched and none was found. The Panel considered that, under the intended conditions of use, the risk of allergic sensitisation and elicitation reactions by dietary exposure cannot be excluded, but the likelihood is considered to be low. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns under the intended conditions of use.

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Safety evaluation of the food enzyme glucan 1,4‐alpha‐glucosidase from the genetically modified Trichoderma reesei strain DP‐Nzh38

Project description:Abstract The food enzyme glucoamylase (4‐α‐D‐glucan glucohydrolase; EC 3.2.1.3) is produced with the genetically modified Trichoderma reesei strain DP‐Nzh38 by Danisco US Inc. The genetic modifications do not give rise to safety concerns. The food enzyme is free from viable cells of the production organism and its DNA. The food enzyme is intended to be used in distilled alcohol production, starch processing for glucose syrup production, baking and brewing processes. Since residual amounts of total organic solids (TOS) are removed by distillation and by purification steps applied during the production of glucose syrups, consequently, dietary exposure was not calculated for these uses. Based on the maximum use levels recommended for baking and brewing processes and individual data from the EFSA Comprehensive European Food Consumption Database, dietary exposure to the food enzyme–TOS was estimated to be up to 5.8749 mg TOS/kg body weight per day. The toxicity studies were carried out with another glucoamylase from T. reesei (strain DP‐Nzh49) considered by the Panel as a suitable substitute. Genotoxicity tests did not raise safety concern. The systemic toxicity was assessed by means of a repeated dose 90‐day oral toxicity study in rats. The Panel identified no observed adverse effect level (NOAEL) at the highest dose tested of 1,149 mg TOS/kg body weight (bw) per day resulting in a margin of exposure of at least 195. Similarity of the amino acid sequence to those of known allergens was searched for and one match was found. The Panel considered that, under the intended conditions of use, the risk of allergic sensitisation and elicitation reactions by dietary exposure cannot be excluded, but the likelihood for this to occur is considered to be low. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns under the intended conditions of use.

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Cleavage of α-1,4-glycosidic linkages by the glycosylphosphatidylinositol-anchored α-amylase AgtA decreases the molecular weight of cell wall α-1,3-glucan in <i>Aspergillus oryzae</i>.

Project description:Aspergillus fungi contain α-1,3-glucan with a low proportion of α-1,4-glucan as a major cell wall polysaccharide. Glycosylphosphatidylinositol (GPI)-anchored α-amylases are conserved in Aspergillus fungi. The GPI-anchored α-amylase AmyD in Aspergillus nidulans has been reported to directly suppress the biosynthesis of cell wall α-1,3-glucan but not to degrade it in vivo. However, the detailed mechanism of cell wall α-1,3-glucan biosynthesis regulation by AmyD remains unclear. Here we focused on AoAgtA, which is encoded by the Aspergillus oryzae agtA gene, an ortholog of the A. nidulans amyD gene. Similar to findings in A. nidulans, agtA overexpression in A. oryzae grown in submerged culture decreased the amount of cell wall α-1,3-glucan and led to the formation of smaller hyphal pellets in comparison with the wild-type strain. We analyzed the enzymatic properties of recombinant (r)AoAgtA produced in Pichia pastoris and found that it degraded soluble starch, but not linear bacterial α-1,3-glucan. Furthermore, rAoAgtA cleaved 3-α-maltotetraosylglucose with a structure similar to the predicted boundary structure between the α-1,3-glucan main chain and a short spacer composed of α-1,4-linked glucose residues in cell wall α-1,3-glucan. Interestingly, rAoAgtA randomly cleaved only the α-1,4-glycosidic bonds of 3-α-maltotetraosylglucose, indicating that AoAgtA may cleave the spacer in cell wall α-1,3-glucan. Consistent with this hypothesis, heterologous overexpression of agtA in A. nidulans decreased the molecular weight of cell wall α-1,3-glucan. These in vitro and in vivo properties of AoAgtA suggest that GPI-anchored α-amylases can degrade the spacer α-1,4-glycosidic linkages in cell wall α-1,3-glucan before its insolubilization, and this spacer cleavage decreases the molecular weight of cell wall α-1,3-glucan in vivo.

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