It has been shown that highly conserved residues that form crucial structural elements of the catalytic apparatus may be used to account for the evolutionary history of enzymes. Using saturation mutagenesis, we investigated the role of a conserved residue (Arg526) at the active site of acylaminoacyl peptidase from hyperthermophilic Aeropyrum pernix K1 in substrate discrimination and catalytic mechanism. This enzyme has both peptidase and esterase activities. The esterase activity of the wild-type enzyme with p-nitrophenyl caprylate as substrate is 7 times higher than the peptidase activity with Ac-Leu-p- nitroanilide as substrate. However, with the same substrates, this difference was increased to 150-fold for mutant R526V. A more dramatic effect occurred with mutant R526E, which essentially completely abolished the peptidase activity but decreased the esterase activity only by a factor of 2, leading to a 785-fold difference in the enzyme activities. These results provide rare examples that illustrate how enzymes can be evolved to discriminate their substrates by a single mutation. The possible structural and energetic effects of the mutations on kcat and Km of the enzyme were discussed based on molecular dynamics simulation studies.

The development of recombinant DNA has made it feasible to produce a wide range of valuable protein products in the bacterium Escherichia coli. Extraction of intracellular protein from E. coli is traditionally achieved by mechanical, chemical or enzymatic disruption technology. In this study, thermolysis, which differs from the traditional ones, is presented for disruption of E. coli cells to release recombinant thermostable enzyme. Heat treatment of E. coli at 80℃ is highly effective to destroy the integrity of the bacterial cell wall and release the recombinant thermostable enzyme. At the same time of disruption, the recombinant thermostable enzyme was partially purified. Moreover, thermolysis was carried out in fermentation broth in situ, which may make it a more applicable approach for industrial-scale processes.

A novel plasmid, pBSR2, was constructed by incorporating a strong lipase promoter and a terminator into the original pBD64. A mature lipase gene from Bacillus subtilis strain IFFI10210, an existing strain for lipase expression, was cloned into the plasmid pBSR2 and transformed into B. subtilis A.S.1.1655. Thus, an overexpression strain, BSL2, was obtained. The yield of lipase is about 8.6mg protein/g of wet weight of cell mass and 100-fold higher than that in B. subtilis strain IFFI10210. The recombinant lipase was puriWed in a three-step procedure involving ammonium sulfate fractionation, ion exchange, and gel Wltration chromatography. Characterizations of the puriWed enzyme revealed a molecular mass of 24 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, maximum activity at 43℃ and pH 8.5 for hydrolysis of p-nitrophenyl caprylate. The values of Km and Vm were found to be 0.37mM and 303 μmolmg-1·min-1, respectively. The substrate speciWcity study showed that p-nitrophenyl caprylate is a preference of the enzyme. The metal ions Ca2+, K+, and Mg2+ can activate the lipase, whereas Fe2+, Cu2+, and Co2+ inhibited it. The activity of the lipase can be increased about 48% by sodium taurocholate at the concentration of 7mM and inhibited at concentrations over 10mM.

The aim of this work was to evaluate the capability of corn steep liquor being a low cost substrate on the recombinant protein production by cultivating recombinant Escherichia coli and increasing the production of hyperthermophilic esterase (HE). The effect of corn steep liquor, mineral salt and trace metals on hyperthermophilic esterase production was investigated by means of a five-level three-factor central composite rotatable design. Optimized values of the factors were determined and a maximum hyperthermophilic esterase production of 251.39 U/ml was obtained. This value equaled the yield by yeast extract and peptone medium on the whole.

To enhance the enantioselectivity of a hyperthermophilic esterase from archaeon Aeropyrum pernix K1 (APE1547), a directed evolution approach is employed to generate mutant library from the native enzyme. A mutation (TBC26) is identified after one round of epPCR. The enantioselectivity of TBC26 is increased up to 2.6-fold compared to that of wild type enzyme. TBC26 contains five amino acid substitutions (R11G, L36P, V223A, I551L, A564T). The five mutation sites are spatially distant to the catalytic center. According to the published crystal structure ofWTand considering the changes of secondary and tertiary structure, here we try to explain the change of enantioselectivity of the TBC26. The results suggest that the change of enantioselectivity of enzyme has a close relationship to the configuration of the enzyme.

HPhA, a recombinant histone-like protein from Pyrococcus horikoshii OT3 strain, has compacting activity with DNA as previously reported. The extreme stability and DNA packaging activity of the HPhA make it a candidate as a DNA carrier. Here, the plasmid DNA-HPhA complexes were fully characterized by gel retardation assay and DNase resistance assay. It was further proved that HPhA has in vitro DNA transfection activity. HPhA-mediated transfection efficiency was dependent on the mass ratio of HPhA to DNA, the incubation time and the presence of calcium. A protocol for HPhA-mediated transfection in vitro was established to improve transfection efficiency. The optimal mass ratio of HPhA to DNAwas 6:1, and the incubation time required for the DNA-HPhA complex to be in contact with the cell was 4 h. In addition, the presence of 2 mM CaCl2 in the cell culture medium was required for efficient transfection. Serum did not show inhibition of HPhA-mediated transfection. Most importantly, the cytotoxicity of HPhA is lower than that of commonly used cationic liposome-based gene delivery systems, and HPhA-mediated transfection in NIH 3T3, HEK 293, HL-7702, HepG2 and Cos 7 cell lines in vitro has a higher efficiency and reproducibility. These results demonstrate that the HPhA is a new, potentially widely applicable and highly efficient gene carrier.

A histone-like gene, PHS051 from hyperthermophilic archaeon Pyrococcus horikoshii OT3 strain, was cloned, sequenced, and expressed in Escherichia coli. The recombinant histone, HPhA, encodes a protein of 70 amino acids with a molecular weight of 7868 Da. Amino acid sequence analysis of HPhA showed high homology with other archaeal histones and eukaryal core histones. The HPhA was purified to homogeneity by heat precipitation and affinity chromatography. Gel electrophoresis mobility shift assays demonstrate that the purified HPhA has high affinity to DNA. The complex of the HPhA and DNA allows DNA to be protected from cleavage by the restriction enzyme TaqI at 65℃. Circular dichroism spectra reveal that the conformation of the recombinant histone HPhA becomes looser when temperatures increase from 25 to 90℃. The HPhA has inherited a remarkable thermostability especially in the presence of 1M KCl and retained DNA binding activity at extreme temperature, which is consistent with our previous report about its structure stability analyzed by X-ray crystallography.

An open reading frame of the hyperthermophilic archaeon Aeropyrum pernix K1 APE2325, which composed of 474 bases, was cloned and expressed in Escherichia coli BL21 (DE3) Codon Plus-RIL. The recombinant protein was puriWed by Ni-chelation aYnity chromatography. It showed a single band with a molecular mass of 18kDa in SDS–PAGE. The puriWed enzyme exhibited both phospholipase A2 and esterase activities with the optimal catalytic temperature at 90℃. The enzyme activity was Ca2+-independent. Kinetic analysis revealed its Km, kcat, and Vm for the p-nitrophenyl propionate substrate were 103μM, 39s-1, and 249μmol/min/mg, respectively. The recombinant protein was thermostable and its half-life at 100℃ was about 1h.

Acylpeptide hydrolases (APH; also known as acylam-ino acid releasing enzyme) catalyze the removal of an N-acylated amino acid from blocked peptides. The crystal structure of an APH from the thermophilic arch-aeon Aeropyrum pernix K1 to 2.1 A resolution confirms it to be a member of the prolyl oligopeptidase family of serine proteases. The structure of apAPH is a sym-metric homodimer with each subunit comprised of two domains. The N-terminal domain is a regular seven-bladed β-propeller, while the C-terminal domain has a canonical α/β hydrolase fold and includes the active site and a conserved Ser445-Asp524-His556 catalytic triad. The complex structure of apAPH with an organo- phosphorus substrate, p-nitrophenyl phosphate, has also been determined. The complex structure unam- biguously maps out the substrate binding pocket and provides a basis for substrate recognition by apAPH. A conserved mechanism for protein degradation from archaea to mammals is suggested by the structural features of apAPH.

A homolog to the eubacteria inorganic pyrophosphatase (PPase, EC 3.6.1.1) was found in the genome of the hyperthermophilic archaeon Pyrococcus horikoshii. This inorganic pyrophosphatase (Pho-PPase) grows optimally at 88℃. To understand the structural basis for the thermostability of Pho-PPase, we have determined the crystal structure to 2.66 A resolution. The crystallographic asymmetric unit contains three monomers related by approximate threefold symmetry, and a hexamer is built up by twofold crystallographic symmetry. The main-chain fold of Pho-PPase is almost identical to that of the known crystal structure of the model from Sulfolobus acidocaldarius. A detailed comparison of the crystal structure of Pho-PPase with related structures from S. acidocaldarius, Thermus thermophilus, and Escherichia colishows significant differences that may account for the difference in their thermostabilities. A reduction in thermolabile residues, additional aromatic residues, and more intimate association between subunits all contribute to the larger thermophilicity of Pho-PPase. In particular, deletions in two loops surrounding the active site help to stabilize its conformation, while ion-pair networks unique to Pho-PPase are located in the active site and near the C-terminus. The identification of structural features that make PPases more adaptable to extreme temperature should prove helpful for future biotechnology applications.