Protein translocation in Escherichia coli

Construction of a cloning system for the mass production of a virus-binding protein specific for poliovirus type 1

In our previous study, virus-binding proteins (VBPs) demonstrating the ability to strongly bind poliovirus type 1 (PV1) were recovered from a bacterial culture derived from activated sludge. The isolated VBPs would be useful as viral adsorbents for water and wastewater treatments. The VBP gene of activated sludge bacteria was isolated, and the cloning system of the VBP was established. The isolation of the VBP gene from DNA libraries for activated sludge bacteria was achieved with the colony hybridization technique. The sequence of the VBP gene consisted of 807 nucleotides encoding 268 amino acids. Fifteen amino acid sequences were retrieved from 2,137,877 sequences by a homology search using the BLAST server at the National Center for Biotechnology Information. The protein encoded in the isolated genome was considered to be a newly discovered protein from activated sludge culture, because any sequences in protein databases were not perfectly matched with the sequence of the VBP. It was confirmed that Escherichia coli BL21 transformed by pRSET carrying the isolated VBP gene could extensively produce the VBP clones. Enzyme-linked immunosorbent assay (ELISA) revealed that the VBP clone exhibited the binding ability with intact particles of PV1. The equilibrium binding constant between PV1 and VBP in the ELISA well was estimated to be 2.1 x 10(7) (M(-1)), which also indicated that the VBP clones have a high affinity with the PV1 particle. The VBP cloning system developed in this study would make it possible to produce a mass volume of VBPs and to utilize them as a new material of the specific adsorbent in several technologies, including virus removal, concentration, and detection.

Sequencing and transcriptional analysis of the chlorite dismutase gene of Dechloromonas agitata and its use as a metabolic probe

The dismutation of chlorite into chloride and O(2) represents a central step in the reductive pathway of perchlorate that is common to all dissimilatory perchlorate-reducing bacteria and is mediated by a single enzyme, chlorite dismutase. The chlorite dismutase gene cld was isolated and sequenced from the perchlorate-reducing bacterium Dechloromonas agitata strain CKB. Sequence analysis identified an open reading frame of 834 bp that would encode a mature protein with an N-terminal sequence identical to that of the previously purified D. agitata chlorite dismutase enzyme. The predicted translation product of the D. agitata cld gene is a protein of 277 amino acids (aa), including a leader peptide of 26 aa. Primer extension analysis identified a single transcription start site directly downstream of an AT-rich region that could represent the -10 promoter region of the D. agitata cld gene. Northern blot analysis indicated that the cld gene was transcriptionally up-regulated when D. agitata cells were grown in perchlorate-reducing versus aerobic conditions. Slot blot hybridizations with a D. agitata cld probe demonstrated the conservation of the cld gene among perchlorate-reducing bacteria. This study represents the first description of a functional gene associated with microbial perchlorate reduction.

Cloning, sequence analysis, and expression in Escherichia coli of the gene encoding an alpha-amino acid ester hydrolase from Acetobacter turbidans

The alpha-amino acid ester hydrolase from Acetobacter turbidans ATCC 9325 is capable of hydrolyzing and synthesizing beta-lactam antibiotics, such as cephalexin and ampicillin. N-terminal amino acid sequencing of the purified alpha-amino acid ester hydrolase allowed cloning and genetic characterization of the corresponding gene from an A. turbidans genomic library. The gene, designated aehA, encodes a polypeptide with a molecular weight of 72,000. Comparison of the determined N-terminal sequence and the deduced amino acid sequence indicated the presence of an N-terminal leader sequence of 40 amino acids. The aehA gene was subcloned in the pET9 expression plasmid and expressed in Escherichia coli. The recombinant protein was purified and found to be dimeric with subunits of 70 kDa. A sequence similarity search revealed 26% identity with a glutaryl 7-ACA acylase precursor from Bacillus laterosporus, but no homology was found with other known penicillin or cephalosporin acylases. There was some similarity to serine proteases, including the conservation of the active site motif, GXSYXG. Together with database searches, this suggested that the alpha-amino acid ester hydrolase is a beta-lactam antibiotic acylase that belongs to a class of hydrolases that is different from the Ntn hydrolase superfamily to which the well-characterized penicillin acylase from E. coli belongs. The alpha-amino acid ester hydrolase of A. turbidans represents a subclass of this new class of beta-lactam antibiotic acylases.

High-level periplasmic expression in Escherichia coli using a eukaryotic signal peptide: importance of codon usage at the 5' end of the coding sequence

We investigated the ability of signal peptides of eukaryotic origin (human, mouse, and yeast) to efficiently direct model proteins to the Escherichia coli periplasm. These were compared against a well-characterized prokaryotic signal peptide-OmpA. Surprisingly, eukaryotic signal peptides can work very efficiently in E. coli, but require optimization of codon usage by codon-based mutagenesis of the signal peptide coding region. Analysis of the 5' of periplasmic and cytoplasmic E. coli genes shows some codon usage differences.

Need for TolC, an Escherichia coli outer membrane protein, in the secretion of heat-stable enterotoxin I across the outer membrane

Escherichia coli heat-stable enterotoxin Ip (STIp) is a typical extracellular toxin consisting of 18 amino acid residues synthesized as a precursor of pre (amino acid residues 1 to 19), pro (amino acid residues 20 to 54), and mature (amino acid residues 55 to 72) regions. STIp synthesized in the cytoplasm must cross the inner and outer membranes to migrate into the extracellular environment. Previous studies showed that the precursor translocates across the inner membrane utilizing the general export pathway consisting of Sec proteins. However, it remains unclear how it crosses the outer membrane. In this study, we examined the effects of mutation of the tolC gene which encodes an E. coli outer membrane protein, TolC, on the release of STIp into the extracellular environment. The mutation reduced the amount of STIp released into culture supernatant and increased the amount of STIp accumulated in the periplasm. This indicates that TolC mediates the translocation of STIp across the outer membrane. The inability to transfer STIp in the periplasm into the culture supernatant was restored by introduction of the tolC gene into the mutant cells. In the mouse intestinal loop assay, living cells of the mutants did not show a positive response, but wild-type cells did. These results showed that TolC is involved in the translocation of STIp across the outer membrane.

Selective separation process of proteins based on the heat stress-induced translocation across phospholipid membranes

Heating of several protein solutions at 40-47 degrees C for 5-60 min in the presence of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes induced the translocation of beta-galactosidase (beta-gal), alpha-glucosidase (alpha-glu) and bovine carbonic anhydrase (CAB) from outer to inner aqueous phase across the liposome membrane. The translocated amounts of beta-gal at various temperatures were maximized under suitable heating conditions (45 degrees C, 30 min). Those of alpha-glu and CAB were maximized at 40-45 and 60 degrees C, respectively. Each maximum value could be correlated with the corresponding local hydrophobicity of each protein evaluated by the aqueous two-phase partitioning method. The possibility to apply these heat-induced translocation phenomena to the bioseparation of proteins was successfully demonstrated for the model mixture solution of beta-gal, alpha-glu and CAB.

The role of the ribosome-translocon complex in translation and assembly of polytopic membrane proteins

Newly synthesized polytopic membrane proteins and secretory proteins often share the same target membrane as their primary destination, and in some cases, the cellular machinery that targets and transfers them into or across the membrane. Unlike secretory proteins, which are localized to the external compartment, each polytopic membrane protein molecule must be partitioned among the cytoplasm, the membrane and the external milieu. How does the ribosome-translocon complex cope with the different domains of polytopic membrane proteins?

The protease-protected 30 kDa domain of SecA is largely inaccessible to the membrane lipid phase

SecA binds to the inner membrane of Escherichia coli through low affinity lipid interactions or with high affinity at SecYEG, the integral domain of preprotein translocase. Upon addition of preprotein and nucleotide, a 30 kDa domain of SecYEG-bound SecA is protected from proteolysis via membrane insertion. Such protection could result from some combination of insertion into the lipid phase, into a proteinaceous environment or across the membrane. To assess the exposure of SecYEG-bound SecA to membrane lipids, a radiolabeled, photoactivatable and lipid-partitioning crosslinker, 3-trifluoromethyl-3-(m[125I]iodophenyl) diazirine benzoic acid ester, was incorporated into inner membrane vesicles. The 30 kDa domain of SecYEG-bound SecA, inserted into the membrane in response to translocation ligands, is 18-fold less labeled than SecY, which is labeled effectively. In contrast, incorporation of the purified 30 kDa SecA fragment into crosslinker-containing detergent micelles or addition of detergent to crosslinker-containing membranes bearing the protease-protected SecA domain readily allows for labeling of this domain. We propose that the protease-inaccessible 30 kDa SecA domain is shielded from the fatty acyl membrane phase by membrane-spanning SecYEG helices and/or is largely exposed to the periplasm.

Cloning and sequence analysis of Vibrio parahaemolyticus ompK gene encoding a 26-kDa outer membrane protein, OmpK, that serves as receptor for a broad-host-range vibriophage, KVP40

The ompK gene of Vibrio parahaemolyticus 1010 (RIMD 2210001) encoding an outer membrane protein (OMP), OmpK, which serves as the receptor for a broad-host-range vibriophage, KVP40, was cloned and sequenced. The gene consisted of 789 nucleotides encoding 263 amino acids. Since the first 20 amino acids most likely constitute the signal peptide, mature OmpK would consist of 243 amino acids with a calculated molecular mass of 27458 Da. Sequence comparisons indicate that OmpK is unique among Vibrio OMPs so far sequenced, but may be distantly related to Tsx of enteric bacteria and is homologous to an Aeromonas hydrophila OMP, protein IV.