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Escherichia coli phytase appA, which hydrolyzes phytate, has been widely applied as an important feed supplement, but its resistance to trypsin needs to be improved. Six putative solvent-accessible amino acid residues (K74, K75, K180, R181, K183, and K363), which could be easily attacked by trypsin, were selected to improve trypsin tolerance of Escherichia coli phytase appA. Inspection of the three-dimensional structure and computational design via hydrogen bond analysis, six optimal mutation sites of K74D/K75Q/K180N/R181N/K183S/K363N, which strengthened the hydrogen bonding, were performed to generate three mutants. Results showed that the most beneficial mutant appA-M6 had a specific activity of 3262 U/mg with molecular weight of approximately 52-55 kDa. Similar to appA-WT, the optimal pH (4.5) and temperature (60 °C) of appA-M6 were unchanged. Compared with appA-WT, appA-M6 showed a significant enhancement (p < 0.05) in resistance to trypsin and a 3.8 °C increase in melting temperature (T m ). We concluded that introduction of hydrogen bonds and N-glycosylation modification resulted in decreased enzyme flexibility and increased the enzyme stability against proteolysis and thermal denaturation. The mutant appA-M6 generated in this study could be applied for the large-scale commercial production of phytase and thus could benefit the food and feed industry.

To produce recombinant Buthus martensii Karsch insect toxin (BmK IT), BmK IT cDNA which fused a hexahistidine sequence at the C-terminus by PCR was inserted into pTWIN1 expression vector fused in frame with an upstream Ssp DnaB intein gene. The expression plasmid was transformed into E. coli BL21 (DE3) strain and protein expression was induced by IPTG. The CBD-Intein-BmK IT(his6) fusion protein was purified from cell lysates using Ni-NTA resin affinity chromatography. The intein was removed from fusion protein by on-column intein-mediated cleavage. BmK IT(his6) was purified through Superdex 75 gel chromatography to more than 95% homogeneity. The purified protein has both correct secondary structure and insecticidal activity.

A gene, rBmK Cta, encoding a chlorotoxin-like peptide from the scorpion, Buthus martensii Karsch, was synthesized according to the sequence optimized for codon usage in Escherichia coli and was expressed in E. coli BL21 (DE3) using a pExSecI expression system in which the IgG-binding domain-ZZ of protein A is fused to the N-terminal of rBmK CTa. The fusion protein, ZZ-rBmK CTa, was expressed in soluble form (7.8 mg l(-1)) and was purified to give a single band on SDS-PAGE. The domain-ZZ of fusion protein ZZ-rBmK CTa was removed by cleavage of an Asn-Gly peptide bond with hydroxylamine. The rBmK CTa was separated from the IgG-binding moiety by a second passage through the IgG affinity column. Western blot analysis demonstrated that this protein was rBmK CTa. Acute toxicity assay in mice demonstrated that the rBmK CTa had an LD(50) value of 4.3 mg kg(-1).

The polypeptide release factor gene, eRF1, of Blepharisma japonicum (Bj-eRF1) was cloned and sequenced. Its coding region was 1314 base pairs and encodes a protein of 437 amino acids. The cloned gene was expressed in Escherichia coli and the recombinant Bj-eRF1 polypeptide was purified by Ni2+-nitrilotriacetic acid agarose and Superose12 chromatography. Pull-down analysis showed that the recombinant Bj-eRF1 interacts with the heterologously-expressed release factor, eRF3C, of Euplotes octocarinatus.

A codon-optimized Escherichia coli appA phytase gene was synthesized and expressed in Pichia pastoris. Two residue substitutions (Q258N, Q349N) were sequentially introduced to enhance its glycosylation activity. Secretion of appA-Q258N/Q349N was approx. 0.3 mg ml and enzyme activity reached 1,030 U ml. Purified appA-Q258N/Q349N had a specific activity of 3,137 U mg with an MW of approx. 53 kDa. Compared with appA-WT, appA-Q258N/Q349N showed over 40 % enhancement in thermostability (85 °C for 10 min) and 4-5 °C increases in the melting temperatures (T). The K and K of appA-Q258N/Q349N were 0.43 mM and 3,058 s, respectively, which are similar with that of appA-WT. The mutant appA-Q258N/Q349N obtained in this study could be used for the large-scale commercial production of phytase. [ABSTRACT FROM AUTHOR]

The nucleotide sequence of a type of chlorotoxin-like peptide, an inhibitor of small-conductance Cl− channels, from the scorpion, Buthus martensii Karsch, was synthesized (named rBmK CTa) according to the sequence optimized for codon usage in E. coli. It was over-expressed using a pExSecI expression system and purified to homogeneity. Polycolonal antibodies to the purified protein were raised in rats. Overlay assay and pull-down assay showed that this toxin specially binds to two proteins in the glioma cells with corresponding molecular weights of about 80 and 35 kDa. They may serve as candidate receptors or alternative cellular component for interaction with rBmK CTa. [ABSTRACT FROM AUTHOR]

Abstract: Class II polypeptide release factor eRF3 stimulates translation termination in a GTP-dependent manner. Recent data show that eRF3 is also involved in cell cycle regulation apart from its function in translation. Here we show that recombinant Eo-eRF3 from the ciliate Euplotes octocarinatus expressed in Escherichia coli can be tested for its ribosome-dependent GTPase activity using an in vitro system. Moreover, polyclonal antibodies against recombinant Eo-eRF3 were used to determine the localization of Eo-eRF3 using immunofluorescence and immunoelectron microscopy, which showed that the Eo-eRF3 is distributed not only around the macronucleus, but also in basal bodies in the cortex of E. octocarinatus cells. The results suggest that Eo-eRF3 may be involved in cytoskeleton organization in addition to its function in translation termination. [Copyright &y& Elsevier]

Abstract: The low yield and poor folding efficiency in vivo of soluble and active recombinant cysteine-rich proteins expressed in Escherichia coli are a major challenge for large-scale protein production and purification. Expression vectors containing Buthus martensii Karsch insect toxin (BmK IT) fused to the C terminus of the intein Ssp DnaB were constructed in an attempt to overcome this problem. Following purification and intein self-cleavage, the fusion protein His6-intein-IT produced insoluble BmK IT, while intein-IT-His6 generated soluble and properly folded BmK IT. This result indicated that the positioning of the His6 tag has a key role in the production of soluble and functional BmK IT. [Copyright &y& Elsevier]

The gene encoding neurotoxin (BmK Mm2) from the scorpion Buthus martensii Karsch was expressed in Escherichia coli BL21 (DE3) at a level of 1.6mg/L using expression plasmid pExSecI system. SDS–PAGE analysis of the cell lysate confirmed that gene BmK Mm2 was expressed in soluble form and the expressed production was secreted into Luria–Bertani (LB) culture medium from Escherichia coli. According to the characters of pExSecI expression system, the IgG binding domain-ZZ of Protein A is fused to the N-terminal of BmK Mm2. Recombinant BmK Mm2 (ZZ-BmK Mm2, pI 6.81, 22.007kDa) was purified rapidly and efficiently by IgG–Sepharose 6 Fast Flow and Superdex-75 gel filtration chromatography, produced a single band on SDS–PAGE. Western blot analysis demonstrated that this protein was recombinant BmK Mm2. The results of MTT assay, morphological observation of nucleus and single cell gel electrophoresis showed that the expressed recombinant BmK Mm2 was toxic for glial cells of mice, which indicate that it has biological activity. [Copyright &y& Elsevier]