[Thermotoga neopolitina gene cluster, participating in degradation of starch and maltodextrins: expression of aglB and aglA gene in Escherichia coli, properties of recombinant enzymes]

The aglB and aglA genes from the starch/maltodextrin utilization gene cluster of Thermotoga neapolitana were subcloned into pQE vectors for expression in Escherichia coli. The recombinant proteins AglB and AglA were purified to homogeneity and characterized. Both enzymes are hyperthermostable, the highest activity was observed at 85 degrees C. AglB is an oligomer of identical 55-kDa subunits capable of aggregation. This protein hydrolyses cyclodextrins and linear maltodextrins to glucose and maltose by liberating glucose from the reducing end of the molecules, and it is a cyclodextrinase with alpha-glucosidase activity. The pseudo-tetrasaccharide acarbose, a potent alpha-amylase and alpha-glucosidase inhibitor, does not inhibit AglB but, on the contrary, acarbose is degraded quantitatively by AglB. Recombinant AglB is activated in the presence of CaCl2, KCl, and EDTA, as well as after heating of the enzyme. AglA is a dimer of two identical 54-kDa subunits, and it hydrolyses the alpha-glycoside bonds of disaccharides and short maltooligosaccharides, acting on the substrate from the non-reducing end of the chain. It is a cofactor-dependent alpha-glucosidase with a wide action range, hydrolysing both oligoglucosides and galactosides with alpha-link. Thereby, the enzyme is not specific with respect to the configuration at the C4 position of its substrate. For the enzyme to be active, the presence of NAD+, DTT, and Mn2+ is required. Enzymes AglB and AglA supplement one another in substrate specificity and ensure complete hydrolysis to glucose for the intermediate products of starch degradation.

Use1p is a yeast SNARE protein required for retrograde traffic to the ER

SNAREs on transport vesicles and target membranes are required for vesicle targeting and fusion. Here we describe a novel yeast protein with a typical SNARE motif but with low overall amino acid homologies to other SNAREs. The protein localized to the endoplasmic reticulum (ER) and was therefore named Use1p (unconventional SNARE in the ER). A temperature-sensitive use1 mutant was generated. use1 mutant cells accumulated the ER forms of carboxypeptidase Y and invertase. More specific assays revealed that use1 mutant cells were defective in retrograde traffic to the ER. This was supported by strong genetic interactions between USE1 and the genes encoding SNAREs in retrograde traffic to the ER. Antibodies directed against Use1p co-immunoprecipitated the SNAREs Ufe1p, myc-Sec20p and Sec22p, which form a SNARE complex required for retrograde traffic from the Golgi to the ER, but neither Bos1p nor Bet1p (members of the SNARE complex in anterograde traffic to the Golgi). Therefore, we conclude that Use1p is a novel SNARE protein that functions in retrograde traffic from the Golgi to the ER.