Optimization of a thermostable lipase from Bacillus stearothermophilus P1: overexpression, purification, and characterization

An expression library was generated from a partial NcoI and HindIII digest of genomic DNA from the thermophilic bacterium, Bacillus stearothermophilus P1. The DNA fragments were cloned into the expression vector pQE-60 and transformed into Escherichia coli M15[EP4]. Sequence analysis of a lipase gene showed an open reading frame of 1254 nucleotides coding a 29-amino-acid signal sequence and a mature sequence of 388 amino acids. The expressed lipase was isolated and purified to homogeneity in a single chromatographic step. The molecular mass of the lipase was determined to be approximately 43 kDa by SDS-PAGE and mass spectrometry. The purified lipase had an optimum pH of 8.5 and showed maximal activity at 55 degrees C. It was highly stable in the temperature range of 30-65 degrees C. The highest activity was found with p-nitrophenyl ester-caprate as the synthetic substrate and tricaprylin as the triacylglycerol. Its activity was strongly inhibited by 10 mM phenylmethanesulfonyl fluoride and 1-hexadecanesulfonyl chloride, indicating that it contains a serine residue which plays a key role in the catalytic mechanism. In addition, it was stable for 1 h at 37 degrees C in 0.1% Chaps and Triton X-100.

Structural modeling and characterization of a thermostable lipase from Bacillus stearothermophilus P1

The moderate thermophilic bacterium Bacillus stearothermophilus P1 expresses a thermostable lipase that was active and stable at the high temperature. Based on secondary structure predictions and secondary structure-driven multiple sequence alignment with the homologous lipases of known three-dimensional (3-D) structure, we constructed the 3-D structure model of this enzyme and the model reveals the topological organization of the fold, corroborating our predictions. We hypothesized for this enzyme the alpha/beta-hydrolase fold typical of several lipases and identified Ser-113, Asp-317, and His-358 as the putative members of the catalytic triad that are located close to each other at hydrogen bond distances. In addition, the strongly inhibited enzyme by 10 mM PMSF and 1-hexadecanesulfonyl chloride was indicated that it contains a serine residue which plays a key role in the catalytic mechanism. It was also confirmed by site-directed mutagenesis that mutated Ser-113, Asp-317, and His-358 to Ala and the activity of the mutant enzyme was drastically reduced.

Purification and characterization of the highly thermostable proteases from Bacillus stearothermophilus TLS33

Three thermostable proteases, designated S, N, and B, are extracellular enzymes produced by Bacillus stearothermophilus strain TLS33. They were purified by lysine affinity chromatography, strong anion exchange Q HyperD chromatography, and Ultrogel AcA44 gel filtration. The molecular masses of the enzymes determined by SDS-PAGE and zymography were approximately 36, 53, and 71 kDa, respectively. Thermostable protease S bound strongly to the lysine affinity column and could be purified by this single step. The optimum pH values of proteases S, N, and B were shown to be 8.5, 7.5, and 7.0, respectively. The maximum activities for the enzymes were at 70, 85, and 90 degrees C, respectively. Proteases S, N, and B at pH 7.0 in the presence of 5 mM CaCl(2) retained half their activities after 30 min at 72, 78, and 90 degrees C, respectively. All three thermostable proteases were strongly inhibited by the metal chelators EDTA and 1,10-phenanthroline, and the proteolytic activities were restored by addition of ZnCl(2). They can thus be classified as Zn(2+) metalloproteases. The cleavage specificities of proteases S, N, and B on a 30-residue synthetic peptide from pro-BPN' subtilisin were Tyr-Ile, Phe-Lys, and Gly-Phe, respectively.

The stereospecific D-glucose transport activity of cholate extracts from human erythrocyte membranes

The glucose transport protein of human erythrocyte membranes was solubilized with cholate to facilitate rapid reconstitution and direct glucose transport measurements. This may simplify the isolation of the native glucose transporter. In most experiments the membranes were prepared from fresh blood within 8 h, frozen in liquid nitrogen and stored at -70 degrees C to minimize proteolytic degradation. Solubilization with 25 mM cholate in the presence of 200 mM NaCl at pH 8.4 for 12 min at room temperature gave a high D-glucose transport activity. The solubilized mixture contained 20% of the total membrane protein, only 6% of the polypeptides of molecular weight around 90000, 23% of the polypeptides of molecular weight around 55000, 30% of the phospholipids and at least 6% of the stereospecific D-glucose transport activity. At cholate concentrations up to 22 mM the ratio of solubilized phospholipids to cholate increased steeply, concomitant with an increase in solubilized activity. Above 30 mM cholate the activity diminished. At 4 degrees C the activity of the extract decreased rapidly within the first day and slowly during the next few days. The initial changes seem to have produced a fairly stable, but not native form or fragment of the transporter. When 20 mM EDTA and 5 mM dithioerythritol were included in the solubilization mixture a high activity was preserved for about one day.

The permeability of bilayer lipid membranes on the incorporation of erythrocyte membrane extracts and the identification of the monosaccharide transport proteins

1. Extracts of the human erythrocyte membrane have been prepared by five different procedures involving Triton X-100 solubilization and gel chromatography. 2. The extracts have been analysed by gel electrophoresis and incorporated asymmetrically into phosphatidylcholine-cholesterol-n-decane planar bilayers. 3. Removal of excess Triton X-100 from membrane extracts or prolonged storage facilities the proteolysis of membrane extracts with the partial or complete breakdown of band 3 polypeptides (notation of Fairbanks, G., Steck, T.L. and Wallach, D.F.H. (1971) Biochemistry 10, 2606--2616) and the appearance of an enhanced zone 4.5 and low molecular weight material. 4. Incorporation of zone 4.5 polypeptides into bilayer lipid membranes increases their permeability to D-glucose at 27 and 5 degrees C. 5. It is suggested that the components of the monosaccharide system are present in band 3 polypeptides but that they can undergo proteolysis with some retention of transport activity.