Juana S. Tandecarz

A glycoprotein multimer fromBacillus thuringiensis sporangia: Dissociation into subunits and sugar composition

Two glycoproteins (205 and 72 kDa) were found inBacillus thuringiensis sporangia. They were predominantly localized in the exosporium and/or the spore coat, although a small proportion was also found in membranes. A method for the dissociation of hydrophobic aggregates that resist the usual conditions of SDS-PAGE is described. Using this method we established that the 205 kDa glycoprotein is a multimer of the 72 kDa one. Deglycosylation of the 205 kDa and 72 kDa glycoproteins with trifluoromethanesulfonic acid yielded a 54 kDa polypeptide in both cases. At least three species of oligosaccharides were O-glycosidically linked to serines of the 54 kDa polypeptide chain. One of the oligosaccharides had N-acetylgalactosamine at the reducing end, rhamnose and a component not yet identified.

Molecular Cloning And Characterization Of The Enzyme Udp-Glucose: Protein Transglucosylase From Potato

Abstract UDP-Glc:protein transglucosylase (UPTG) (EC 2.4.1.112) is an autocatalytic glycosyl-transferase previously postulated as a protein that primes starch biosynthesis. Polyclonal antibodies raised against UPTG purified from potato ( Solanum tuberosum L.) tubers were used to screen a potato swelling stolon tip cDNA expression library. The isolation, cloning and sequencing of two cDNAs corresponding to UPTG are described. Recombinant UPTG was labelled after incubation with UDP-[ 14 C]-Glc and Mn 2+ , indicating that it was enzymatically active. It was determined that purified as well as recombinant UPTG can be reversibly glycosylated by UDP-Glc, UDP-Xyl or UDP-Gal. RNA hybridization studies and western blot analysis indicate that UPTG mRNA and protein are expressed in all potato tissues. Databank searches revealed a high degree of identity between UPTG and several plant sequences that encode for proteins with apparent localization at the cytoplasmic face of the Golgi apparatus and at plasmodesmata. The biochemical properties of UPTG and the apparent lack of a signal peptide that could allow its entrance into plastids argue against the postulated role of UPTG in starch synthesis and point towards a possible role of the protein in the synthesis of cell wall polysaccharides.

Biosynthesis of starch. Formation of a glucoproteic acceptor by a potato non-sedimentable preparation.

1. A non-sedimentable fraction of potato tuber has been found to catalyze [14C]glucose transfer from [14C]glucose 1-phosphate to an endogenous proteic acceptor in the absence of added primer. This transfer is activated by Mn2+. 2. The labeled glucosylated product formed is trichloroacetic acid insoluble and sensitive to proteolytic and amylolytic digestions. It appears to be a glucoprotein with glucosyl chains bound to the peptide portion of the molecule through an unknown linkage. 3. The carbohydrate portion of the glucoprotein can be released by prolonged incubations with the enzymatic preparation, and becomes in turn, trichloroacetic acid soluble and alcohol precipitable. 4. Both products, the glucoprotein as well as the alpha-1,4-glucan that seems to arise from the enzymatic cleavage of the former, can be used as primers by the transglucosylating system with ADP[14C]glucose, UDP[14C]glucose or GDP[14C]glucose as glucosyl donors. The results presented in this paper are the first demonstration of soluble glucosyl transferases with the same glucose donor specificity to that of the particulate starch synthetase. 5. This report presents further evidence in favor of the assumption of a glucoproteic intermediate in alpha-a,4-glucan synthesis initiation.

UDP-glucose:protein transglucosylase in developing maize endosperm

Abstract UDP-Glc:protein transglucosylase (UPTG) (EC 2.4.1.112), involved in the first step of a two-step mechanism proposed in potato tuber for protein-bound α-glucan synthesis, was found in developing maize endosperm. The enzyme transfers glucosyl residues from UDP-[14C]glucose to an endogenous protein acceptor in a Mn2+-dependent reaction in the absence of added primer. After SDS-polycrylamide gel electrophrresis of the reaction product, radioactivity co-migrated with a 38-kDa protein band. A two-step experiment shows that the developing endosperm of maize contains phosphorylase and starch synthase, capable of utilizing the UPTG reaction product formed during the first step as a primer for the synthesis of protein-bound glucan in the presence of the respective glucosyl donors during the second incubation step.

A two-step enzymatic formation of a glucoprotein in potato tuber.

Evidence is presented on the occurrence of a two-step mechanism for the synthesis of protein bound glucan in a potato tuber particulate preparation. Experiments carried out with a differently labeled sugar donor for each step enabled the isolation of a double-labeled glucoprotein. Smith periodate degradation of the product confirmed this hypothesis.

Enzymatic glycosylation of steroid alkaloids in potato tuber

Abstract The glycosylating activities of two enzymatic preparations from potato tubers were compared, using β-sitosterol and β-solanidine as substrate. The 25 000 g fraction synthesized steryl glucoside (SG) and acylsteryl glucoside (ASG) when β-sitosterol as well as β-solanidine was included in the reaction mixture. The AS fraction formed SG but not ASG from β-sitosterol and glycosylated β-solanidine forming six different derivatives. We tentatively related these products to the six components of solanine: α-, β- and γ-solanine and α-, β- and γ-chaconine.

alpha-Glucan synthesis on a protein primer, uridine diphosphoglucose: protein transglucosylase I. Separation from starch synthetase and phosphorylase and a study of its properties

It was found that the DEAE-cellulose-treated UDP-Glc:protein transglucosylase I catalyzing the first step (reaction 1) in the formation of alpha-glucan bound to protein in potato tuber is not only specific for the glucosyl donor but also for the endogenous acceptor. A single radioactive 38-kDa macromolecular component appeared during denaturing polyacrylamide gel electrophoresis of reaction 1 product. The labeled component is probably the polypeptide subunit of the endogenous acceptor which is being glucosylated. The radioactivity incorporated in reaction 1 product was isolated from a protease digest as a low-molecular-mass glucopeptide fraction. A beta-elimination reaction carried out in the presence of a reducing agent demonstrated that only one glucosyl moiety is transferred from UDP-Glc to the aminoacyl residue, thus forming an O-glucosidic linkage. 3H-labeled sodium borohydride showed that serine and threonine are involved in the peptide bond to glucose. Ion-exchange chromatography on DEAE-cellulose, affinity chromatography on concanavalin-A--Sepharose, gel filtration on Sephacryl S-300 and sucrose density gradient centrifugation failed to separate the enzyme catalyzing reaction 1 from the endogenous acceptor.

Studies on potato tuber phosphorylase-catalyzed reaction in the absence of an exogenous acceptor ☆: I. Characterization and properties of the enzyme

Abstract Phosphorylase II from potato tuber has been subjected to several purification procedures in order to: (a) separate the unprimed activity from the primed one coexisting in the enzymatic preparation, and (b) eliminate endogenous glucan and/or glycoproteins. Large-scale analytical nondenaturing gel electrophoresis and affinity chromatography on concanavalin A-Sepharose 4B succeeded in removing endogenous glycoproteins without any effect on the unprimed activity. In addition, phosphorolysis or glucoamylase treatment of the enzymatic preparation did not abolish the phosphorylase-catalyzed reaction in the absence of an exogenous acceptor. However, no separation between both activities, primed and unprimed, could be achieved either by the above-mentioned methods or by sucrose density gradient centrifugation. Based on sodium dodecyl sulfate-urea-gel electrophoresis, a molecular weight of about 96,000 was found for the phosphorylase II subunit. Molecular weight determination by nondenaturing gel electrophoresis at 5, 6, 7, and 8% acrylamide and by ultracentrifugation on sucrose density gradients suggested that the native enzyme is a dimer, as are other phosphorylases.

Steryl glucoside and acyl steryl glucoside formation in the amyloplast membrane during the development of potato tuber

Abstract Steryl glucoside (SG) and acylated steryl glucoside (ASG) synthesis was investigated in amyloplast membranes from young, intermediate and mature potato tubers. The synthesis ratio SG/ASG was lowest in young tubers (3:2) and highest in mature tubers (6:1). About a 3-fold stimulation of [14C] glucose incorporation into a mixture of SG was observed in amyloplast membranes from mature tubers in the presence of β-sitosterol, while radioactivity incorporation in young tubers was unaffected, thus indicating that different availabilities of endogenous acceptors occur in the membranes. The enzymes involved in sterol modification exhibit a different behavior towards Triton X-100, depending on the developmental stage of the tubers. Low concentrations of the detergent (0.045%) are required to stimulate the enzymes present in young tuber membranes (2-fold). On the other,hand, 0.15% of Triton increased the enzymatic activity in mature tubers 5-fold. These results, together with those obtained after studies of pH dependence, could be related to the lipidic structure of the vesicles formed at different developmental stages of the tubers. It is concluded that the major changes in the enzymatic activities occur as a consequence of the sterol acceptors and acyl donor content during potato tuber growth.

alpha-Glucan synthesis on a protein primer. A reconstituted system for the formation of protein-bound alpha-glucan

Reconstitution experiments with the DEAE-cellulose-treated enzymes, engaged in a two-step mechanism of synthesis of alpha-glucan bound to protein, are performed. Urea/sodium dodecyl sulfate/polyacrylamide gel electrophoretic analysis of the radioactive products synthesized by the reconstituted system shows highly glucosylated, labeled bands, whose apparent molecular masses change with the acrylamide concentration in the gels. The long carbohydrate chains synthesized during the second step arise from the sequential addition of glucosyl moieties to the glucoprotein formed during the first step. A deglucosylation experiment confirms that the product of the reconstituted system originates from the 38-kDa glucosylated component of the reaction 1 product by the addition of beta-amylase-sensitive glucosyl moieties. Our data suggest that specific phosphorylases and starch synthetases are found in potato tuber, which are capable of utilizing reaction 1 product as primer for the synthesis of protein-bound glucan.