[Diagnostic value of serum soluble interleukin-2 receptor levels in interstitial pneumonia of the patients with hematological disorders]

Serum levels of soluble interleukin-2 receptor (SIL-2R) and C-reactive protein (CRP) were measured in 12 patients with interstitial pneumonia (IP) and 10 patients with bacterial pneumonia (BP) of hematological malignancies. Mean SIL-2R levels (U/ml) were 394 +/- 140 in normal controls, 755 +/- 320 in BP, and 2328 +/- 943 in IP. A significantly higher level was found in IP than BP (p < 0.05). Moreover, the SIL-2R/CRP ratio which was over 260 in all cases of IP completely distinguished IP from BP. Levels of SIL-2R rose before the onset of IP and were closely associated with clinical course in most cases. From these results, measurement of serum SIL-2R may be useful for the diagnosis and monitoring of the clinical course of IP complicated with hematological diseases.

Isolation and characterization of the human chromosomal gene for prostacyclin-stimulating factor

Prostacyclin-stimulating factor (PSF) is a protein which acts on vascular endothelial cells and stimulates the production of prostacyclin. Recently, we were able to purify PSF from the conditioned medium of cultured human diploid fibroblasts and clone PSF cDNA. In this study, we screened a human genomic library and isolated genomic clones to determine the structure of the human chromosomal PSF gene. By determining the nucleotide sequence and transcription initiation site of this gene, we found that it comprises 5 exons and 4 introns. Southern hybridization analysis indicated the presence of a single copy of the PSF gene per haploid set of chromosomes. The 300 bp upstream of the transcription initiation site had a very high GC content, and 7 binding sites for the transcription regulating factor Sp1 were present.

SNAP-25 is present on chromaffin granules and acts as a SNAP receptor

SNAP-25 is located on the plasma membrane and essential for exocytosis of neurotransmitters. It was suggested that SNAP-25 and syntaxin 1 via the interaction with VAMP-2 located on synaptic vesicles mediate the docking of the vesicles with the plasma membrane. In the present study, by means of biochemical and morphological analyses, we showed that SNAP-25 is present on chromaffin granules as well as on the plasma membrane. Reconstitution and immunoprecipitation analyses revealed that SNAP-25 on chromaffin granules has essentially the same properties as does SNAP-25 on the plasma membrane.

Characterization of a potential catalytic residue, Asp-133, in the high affinity ATP-binding site of Escherichia coli SecA, translocation ATPase

The high affinity ATP-binding site of SecA is located in its amino-terminal domain possessing amino acid sequences, the Walker A (GXXXXGKT) and B (ZZZZD) motifs, that are characteristic of a major class of nucleotide-binding sites (Walker, J. E., Saraste, M., Runswick, M. J., and Gay, N. J. (1982) EMBO J. 1, 945-951). Recently, we proposed that proteins possessing a typical set of Walker A and B motifs contain a conserved Glu or Asp between the two motifs. This Glu or Asp acts as a "catalytic residue" that activates a water molecule for an in-line attack on the gamma-phosphate of ATP (Amano, T., Yoshida, M., Matsuo, Y., and Nishikawa, K.(1995) FEBS Lett. 359, 1-5). In the present study, the aspartate residue at position 133 in Escherichia coli SecA, which could be the "catalytic residue," was mutated to an asparagine. The mutant SecA (SecA D133N) protein was expressed in E. coli CK4706, encoding a duplication of the secA gene, and purified to homogeneity. The in vitro protein translocation activity and membrane vesicle stimulated ATPase activity of SecA D133N were drastically reduced. Proteolytic studies indicated that the conformational changes of the mutant SecA occurring on interaction with ATP, presecretory proteins, phospholipids, and membrane vesicles, were similar to those of wild-type SecA. The mutant SecA allowed the signal peptide cleavage of proOmpA during translocation, indicating that the mutant retains the ability to bind ATP to perform the initial step of the translocation reaction. These data indicate that the carboxyl group of Asp-133 plays a role as a catalytic carboxylate, which activates a water molecule to attack gamma-phosphate of ATP, and the mutant lacking this residue cannot perform the total translocation but can still perform the initial step of the protein translocation.

Inhibition of vesicle-mediated protein transport by nordihydroguaiaretic acid

Nordihydroguaiaretic acid (NDGA) blocks intra-Golgi protein transport in a cell-free system and prolactin secretion from GH3 cells [Tagaya, M., Henomatsu, N., Yoshimori, T., Yamamoto, A., Tashiro, Y., and Fukui, T. (1993) FEBS Lett. 324, 201-204]. To determine which intracellular secretory pathway(s) is inhibited by NDGA, we investigated its effect on the transport of the vesicular stomatitis virus-encoded glycoprotein in BHK-21 cells. NDGA blocked protein transport from the endoplasmic reticulum to the Golgi apparatus, and from the trans-Golgi network to the plasma membrane. In addition, it retarded the brefeldin A-induced retrograde transport of mannosidase II to the endoplasmic reticulum. Although NDGA had an inhibitory effect on protein synthesis, it induced the expression of BiP, a chaperone located in the endoplasmic reticulum. The induction of BiP may be a consequence of the inhibition of protein transport by NDGA.

SNAP prevents Mg(2+)-ATP-induced release of N-ethylmaleimide-sensitive factor from the Golgi apparatus in digitonin-permeabilized PC12 cells

The N-ethylmaleimide-sensitive factor (NSF), which is involved in the multisteps of protein transport, is released from Golgi membranes on in vitro incubation with Mg(2+)-ATP. However, several lines of evidence suggest that NSF is associated with membranes in spite of the presence of Mg2+ and ATP in vivo. We have used digitonin-permeabilized PC12 cells to investigate the mechanism underlying the association of NSF with membranes. In PC12 cells, immunoreactivity for NSF was observed in the nuclear membranes, the Golgi apparatus, and neuronal growth cones, where synaptic vesicles are concentrated. NSF associated with the Golgi apparatus was released on incubation with Mg(2+)-ATP, whereas NSF in the nuclear membranes and neuronal growth cones was not released on the same treatment. The addition of cytosol blocked the Mg(2+)-ATP-induced release of NSF from the Golgi apparatus. Chromatographic analyses revealed that the factor(s) that prevents NSF release from the Golgi apparatus was eluted at the same position as the soluble NSF attachment proteins (SNAPs). Purified His6-tagged alpha-SNAP exhibited such activity. His6-tagged alpha-SNAP also prevented the Mg(2+)-ATP-induced release of NSF from isolated Golgi membranes.

Effects of oral taurine supplementation on lipids and sympathetic nerve tone

OBJECTIVES

To assess effects of oral taurine supplementation on lipids and sympathetic nerve tone in healthy young men on experimental high fat and cholesterol diets.

METHODS

Twenty-two healthy male volunteers, aged 18-29 years, were recruited for this randomized control trial after informed consent according to the Ethical Committee of Shimane Medical University. Volunteers were randomly allocated into 2 study groups and given experimental diet of identical regimen [total calorie 2500 kcal, cholesterol 1000 mg, polyunsaturated fat/saturated fat (P/S) ratio 0.52, fat 40% of total energy intake (%E), protein 14%E, carbohydrate 46%E] to raise serum cholesterol (CHO) level for 3 weeks. Alcohol intake, smoking and strenuous physical activities were prohibited. Taurine powder (6 g/day) was supplied to one group (T-group, N = 11) and placebo capsules to the other (C-group, N = 11), by a single-blind approach. Blood samples and 24 h urine specimens were obtained once every week. Two men in the C-group dropped out due to upper respiratory infection. There were no difference in age, body mass index (BMI) or blood pressure (BP) between the groups. Statistical analysis was performed by analysis of variance (ANOVA, repeated measurement) and Student's t-test.

RESULTS

There were no changes in BMI and BP in either group during the period. Significant increases in total CHO (25.4 +/- 17.5 mg/dl, mean +/- SD), LDL-CHO (17.1 +/- 14.5) and LDL (43.9 +/- 37.6) were observed in C-group but were attenuated in the T-group. The T-group showed significant increases in VLDL-CHO, VLDL and TG. The T-group had significantly lower urinary norepinephrine excretion than the C-group in the last week.

CONCLUSION

Oral taurine supplementation attenuated increases in T-CHO, LDL-CHO and LDL in healthy men on high fat cholesterol diets but induced significant increases in VLDL-CHO, VLDL and TG, which could be explained by a possible effect of taurine on lipoprotein lipase. Significantly lower urinary norepinephrine excretion observed by the taurine administration implies the suppression of the sympathetic nervous system.

Stepwise movement of preproteins in the process of translocation across the cytoplasmic membrane of Escherichia coli

Derivatives of proOmpA possessing the second cysteine residue at position +302 and the first one at different positions were constructed at the DNA level. They were oxidized to form disulfide-bridged loops of different sizes at different positions. In the presence of a protonmotive force, proOmpAs possessing a smaller loop could be translocated across the membrane in vitro, whereas ones possessing loops comprising more than 16 amino acid residues were hard to translocate. The sizes of polypeptide chains that had been translocated and had become protease-resistant were determined in both the presence and absence of the protonmotive force. The size was the same for all proOmpAs possessing the first cysteine residue between +244 (proOmpA L59) and +274 (proOmpA L29). When the first cysteine residue was moved further away from the N terminus, a sudden increase in size, of approximately 30 amino acid residues, was observed, the size being the same for proOmpAs possessing the first cysteine residue between +278 (proOmpA L25) and +293 (proOmpA L10). The shift in size between proOmpA L29 and proOmpA L25 was observed with different proteases exhibiting different substrate specificities. Treatment with these proteases resulted in complete digestion of SecA on everted membrane vesicles, whereas Sec proteins integrated into membranes were considerably resistant to the treatment. These results can be best interpreted as that the translocation of preproteins through the secretory machinery takes place in every 30 amino acid residues and that SecA is responsible for the stepwise movement.

Preferential interaction of Sec-G with Sec-E stabilizes an unstable Sec-E derivative in the Escherichia coli cytoplasmic membrane

SecY, SecE and SecG form a membrane part of the protein translocation machinery. A SecG-overproducing plasmid was constructed by placing the secG gene under the control of the tac promoter. From the extent of SecG overproduction, the number of SecG molecules in one normal cell was estimated to be about 1,000, which is similar to those of SecY and SecE. Overproduction of SecG stabilized the overproduction of SecE-C, an unstable truncated derivative of SecE, as effectively as SecY does. SecG overproduction also stabilized the overproduction of SecY. However, the SecG-dependent stabilization of SecY was less potent than the SecE-dependent stabilization. These results indicate that SecG preferentially interacts with SecE, which associates with SecY, the SecG-SecE-SecY complex thus being formed in the cytoplasmic membrane.

Ethnicity, environment and salt-sensitivity in cardiac study: epidemiological implications for prevention

1. An association between Na and blood pressure (BP) was studied in the Cardiovascular Diseases and Alimentary Comparison (CARDIAC) Study, an international cross-sectional epidemiological study, involving 55 populations from 25 nations. 2. The partial regression coefficient of BP against 24 h urinary Na was calculated in a multiple linear regression model, by adjusting other confounding factors. This demonstrated different distribution in each of several groups stratified according to their ethnicity and geographical location. 3. The relationship of urinary K to BP regression against urinary Na excretion was investigated to clarify its role in the association of Na with BP. 4. Urinary Na/K ratio showed a significant inverse linear relationship with the regression coefficient of BP on urinary Na excretion among seven Japanese populations. 5. The effect of K was to increase urinary Na excretion, as the ratio of Na/K might modify the association between Na and BP.

Syntaxin 1 (HPC-1) is associated with chromaffin granules

Syntaxin 1 (HPC-1), a component of the receptor for SNAPs (soluble N-ethylmaleimide-sensitive factor attachment proteins), has been implicated in the docking and fusion of synaptic vesicles with the plasma membrane. It was reported that syntaxin 1 in rat brain and chromaffin cells (PC12) is exclusively located on the plasma membrane (Bennett, M. K., Calakos, N., and Scheller, R. H. (1992) Science 257, 255-259; Söllner, T., Bennett, M. K., Whiteheart, S. W., Scheller, R. H., and Rothman, J. E. (1993) Cell 75, 409-418). By means of biochemical and morphological analyses, we now show that syntaxin 1 is associated with chromaffin granules in the adrenal medulla. This finding raises the possibility that syntaxin 1 in chromaffin cells is a component of vesicle-SNAP receptor as well as one of target-SNAP receptor on the plasma membrane.

The C terminus of SecA is involved in both lipid binding and SecB binding

Using C-terminal deletion mutations in secA, we localized the previously proposed (Breukink, E., Keller, R.C. A., and de Kruijff, B. (1993), FEBS Lett. 331, 19-24) second lipid binding site on SecA. Since removal of these residues completely abolished the property of SecA to cause aggregation of negatively charged phosphatidyl-glycerol vesicles, we conclude that the C-terminal 70 amino acid residues of SecA are involved in lipid-binding. The C-terminal 70 amino acid residues of SecA are important for efficient in vitro translocation of the SecB-dependent precursor of PhoE across inverted inner membrane vesicles. Moreover, in vivo studies showed that this region is essential for growth. SecB and a SecB-precursor complex were shown to inhibit the SecA-mediated lipid vesicle aggregation, suggesting that the overall acidic SecB protein binds at or near the second lipid binding site on SecA. This together with the observation that the SecA mutant protein lacking the C-terminal 70 residues had a strongly reduced ability to mediate binding of SecB-precursor complexes to inverted inner membrane vesicles demonstrates that the C terminus of SecA is also involved in SecB binding.

Purification and molecular cloning of prostacyclin-stimulating factor from serum-free conditioned medium of human diploid fibroblast cells

We attempted to identify the factor that stimulated prostacyclin (PGI2) production using conditioned medium from cultured human diploid fibroblast cells subjected to a series of purification steps using h.p.l.c. on DEAE-5PW, Heparin-5PW, Protein-Pak 300, and an insulin-like growth factor-1 ligand affinity column. The purified prostacyclin-stimulating factor (PSF) ran as a single band with a molecular mass of 31 kDa by SDS/PAGE. Analysis of the purified PSF by C4 reversed-phase h.p.l.c. showed a single sharp peak in 31% (v/v) acetonitrile. The material was purified 8000-fold with an overall yield of about 18%. The purified PSF stimulated PGI2 production by cultured bovine aortic endothelial cells at a concentration of about 10 ng/ml; maximal stimulation was achieved at a concentration of 25 ng/ml. A cDNA coding for PSF was cloned and sequenced, revealing an apparently novel protein with no obvious sequence similarity to known proteins.

Reconstitution of an efficient protein translocation machinery comprising SecA and the three membrane proteins, SecY, SecE, and SecG (p12)

A cytoplasmic membrane protein, p12, of Escherichia coli was discovered as a new factor that stimulates the protein translocation activity reconstituted with SecA, SecY, and SecE (Nishiyama, K., Mizushima, S., and Tokuda, H. (1993) EMBO J. 12, 3409-3415). Direct involvement of p12 in protein translocation was subsequently demonstrated in vivo by genetic studies, and the name SecG has been proposed for p12 (Nishiyama, K., Hanada, M., and Tokuda, H. (1994) EMBO J. 13, 3272-3277). To elucidate the role of SecG in protein translocation and to characterize the translocation apparatus comprising these four Sec proteins, the activity of reconstituted proteoliposomes was examined in detail as a function of the amount of each component. SecG markedly stimulated the translocation activity over wide ranges of amounts of the other three Sec proteins, indicating that none of the other three Sec proteins substitutes for the SecG function. Detailed kinetic analyses indicated that the activity of proteoliposomes was dependent on the amount of the SecY-SecE complex when SecG was absent and the amount of the SecY.SecE.SecG complex when the proteoliposomes contained SecG. The translocation activity of the latter complex was significantly higher than that of the former one. Binding of SecA to liposomes appreciably increased when they contained both SecY and SecE, whereas the further presence of SecG did not enhance the binding. On the other hand, the ATPase activity of SecA, which was dependent on proOmpA and SecY.SecE-containing proteoliposomes, was significantly enhanced when the proteoliposomes contained SecG. Taken together, these results indicate that SecG enhances the translocation activity of the apparatus after the step of SecA targeting to SecY.SecE.

Expression of prostacyclin-stimulating factor, a novel protein, in tissues of Wistar rats and in cultured cells

We recently purified and cloned a newly identified PGI2-stimulating factor (PSF). In the present study, we examined the PSF expression in the tissues of Wistar rats and in cultured cells, such as fibroblast cells (FCs), endothelial cells (ECs), and smooth muscle cells (SMCs). The expression of PSF was observed in many tissues of Wistar rats, such as brain, lung, liver, kidney, skeletal muscle, and fat tissue. Especially, lung and kidney showed a greater expression than the other tissues. PSF was also expressed in cultured FCs, ECs, and SMCs. These results indicate that PSF is conserved over species, suggesting that PSF plays a significant role in regulating PGI2 production.

Band 1 subunit of Escherichia coli preportein translocase and integral membrane export factor P12 are the same protein

Escherichia coli preprotein translocase consists of the peripheral membrane protein SecA and the integral membrane domain SecY/E. SecY/E, whether isolated chromatographically or by immunoprecipitation, was found to be complex of three polypeptides, SecY, SecE, and band 1. Band 1 did not correspond to a known sec gene product. The independent purification of the separate integral membrane polypeptides needed for reconstitution of translocation yielded SecY, SecE, and a protein that we termed P12. Based on the sequence of P12, we have prepared antisera to a carboxyl-terminal peptide domain and shown that this antiserum specifically labels only P12 on immunoblots of inner membrane vesicles. We now report that affinity-purified anti-P12 antibodies specifically label the band 1 subunit of the SecY/E complex, whether the SecY/E was isolated chromatographically or by precipitation with antibodies to an epitope-tagged SecY subunit. In addition, the antiserum to P12 can specifically immunoprecipitate the full three-subunit SecY/E complex from detergent extracts. This finding completes the identification of the polypeptides that are essential for catalysis of preprotein translocation.

SecF stabilizes SecD and SecY, components of the protein translocation machinery of the Escherichia coli cytoplasmic membrane

The effect of the overproduction of SecF encoded by the tac-secF gene on a plasmid on the synthesis of other Sec proteins was studied in Escherichia coli. SecF overproduction resulted in the simultaneous overproduction of SecD encoded by the tac-secD gene on a plasmid. Deletion of the orf6 gene, located downstream of the secF gene, had no effect on SecD overproduction. A pulse-chase experiment revealed that the overproduction was due to stabilization of SecD with SecF. SecF overproduction also resulted in the overproduction of SecY encoded by the tac-secY gene on a plasmid as well. SecF overproduction also enhanced the level of SecY expressed by the chromosomal secY gene. This SecF effect was not due to its effect on SecD or SecE, since SecF overproduction did not affect the levels of SecD and SecE expressed by the chromosomal secD and secE genes, respectively. SecE-dependent overproduction of SecY has already been demonstrated. It is suggested that SecF interacts with both SecD and SecY. SecE-SecY interaction has been demonstrated. It is likely, therefore, that all Sec proteins in the cytoplasmic membrane interact with each other.

A periplasmic intermediate in the extracellular secretion pathway of Pseudomonas aeruginosa exotoxin A

Pseudomonas aeruginosa exotoxin A is synthesized with a secretion signal peptide typical of proteins whose final destination is the periplasm. However, exotoxin A is released from the cell without a detectable periplasmic pool, suggesting that additional determinants in this protein are important for recognition by a specialized machinery of extracellular secretion. The role of the N terminus of the mature exotoxin A in this recognition was investigated. A series of exotoxin A proteins with amino acid substitutions for the glutamic acid pair at the +2 and +3 positions were constructed by mutagenesis of the exotoxin A gene. These N-terminal acidic residues of the mature exotoxin A protein were found to be important not only for efficient processing of the precursor protein but also for extracellular localization of the toxin. The mutated exotoxin A proteins, in which a glutamic acid at the +2 position was replaced by a lysine or a double substitution of lysine and glutamine for the pair of adjacent glutamic acids, accumulated in precursor forms in the mixed cytoplasmic and membrane fractions, which was not seen with the wild-type exotoxin A. The processing of the precursor form of one exotoxin A mutant, in which the glutamic acid at the +2 position was replaced with a glutamine, was not affected. Moreover, a substantial fraction of the mature forms of all three mutants of exotoxin A accumulated in the periplasm, while wild-type exotoxin A could be detected only extracellularly. The periplasmic pools of these variants of exotoxin A could therefore represent the intermediate state during extracellular secretion. The signal for extracellular localization may be located in a small region near the amino terminus of the mature protein or could consist of several regions that are brought together after the polypeptide has folded. Alternatively, the acidic residues may be important for ensuring a conformation essential for exotoxin A to traverse the outer membrane.

Histidine residues are involved in translocation-coupled ATP hydrolysis by the Sec-A protein

Treatment of SecA, an essential component of the protein translocation machinery of Escherichia coli, with a histidine-specific reagent, diethylpyrocarbonate, caused significant abolition of its translocation-coupled ATPase (translocation ATPase) activity, which requires a presecretory protein and membrane vesicles, whereas its endogenous ATPase (SecA-ATPase) activity was enhanced by a factor of 2. Diethylpyrocarbonate-treated SecA exhibited an absorption maximum at 240 nm due to the formation of N-carbethoxyhistidine. Upon the modification of about 5 of the total 22 histidine residues in the SecA molecule, both the abolition of its translocation ATPase activity and the enhancement of its SecA-ATPase activity occurred. Intact and modified SecA exhibited similar affinities for ATP, proOmpA and membranes, whereas Vmax of the translocation ATPase activity was significantly lower in the case of the modified SecA. ATP had no effect on the modification of SecA. Taken together, these results indicate that histidine residues susceptible to diethylpyrocarbonate are essential for the translocation ATPase, but not directly involved in the binding of ATP, proOmpA and membranes. A possible reason for the abolition of translocation ATPase is discussed.

A novel membrane protein involved in protein translocation across the cytoplasmic membrane of Escherichia coli

A novel factor, which is a membrane component of the protein translocation machinery of Escherichia coli, was discovered. This factor was found in the trichloracetic acid-soluble fraction of solubilized cytoplasmic membrane. The factor was purified to homogeneity by ion exchange column chromatographies and found to be a hydrophobic protein with a molecular mass of approximately 12 kDa. The factor caused > 20-fold stimulation of the protein translocation when it was reconstituted into proteoliposomes together with SecE and SecY. SecE, SecY, SecA and ATP were essential for the factor-dependent stimulation of the activity. The factor stimulated the translocation of all three precursor proteins examined, including authentic proOmpA. Stimulation of the translocation of proOmpF-Lpp, a model presecretory protein, was especially remarkable, since no translocation was observed unless proteoliposomes were reconstituted with the factor. Partial amino acid sequence of the purified factor was determined. An antibody raised against a synthetic peptide of this sequence inhibited the protein translocation into everted membrane vesicles, indicating that the factor is playing an important role in protein translocation into membrane vesicles. The partial amino acid sequence was found to coincide with that deduced from the reported DNA sequence of the upstream region of the leuU gene. Cloning and sequencing of the upstream region revealed the presence of a new open reading frame, which encodes a hydrophobic protein of 11.4 kDa. We propose that the factor is a general component of the protein translocation machinery of E. coli.

OmpF-Lpp signal sequence mutants with varying charge hydrophobicity ratios provide evidence for a phosphatidylglycerol-signal sequence interaction during protein translocation across the Escherichia coli inner membrane

Using inverted Escherichia coli inner membrane vesicles we have analyzed the phosphatidylglycerol dependence of translocation of an OmpF-Lpp fusion protein carrying a signal sequence with varying positive charge at the N terminus and a hydrophobic core of varying length. It is shown that there is a direct relationship between the phosphatidylglycerol requirement of translocation and the requirement within the translocation process for positive charges on the signal sequence. This provides further evidence that the negative head group of the lipid is required for functional interaction with the positively charged N terminus of the signal sequence.

Phosphatidylglycerol dependent protein translocation across the Escherichia coli inner membrane is inhibited by the anti-cancer drug doxorubicin. Evidence for an electrostatic interaction between the signal sequence and phosphatidylglycerol

OmpF-Lpp, a model secretory protein, requires both a positively charged signal sequence and phosphatidylglycerol (PG) for efficient translocation across the E. coli inner membrane. Modification of the signal sequence can, however, remove both these prerequisites for translocation providing OmpF-Lpp mutants which undergo either PG and charge dependent or PG and charge independent translocation. Here we show that positively charged membrane interactive compounds (polylysine & doxorubicin) are able to inhibit PG dependent translocation of the OmpF-Lpp signal sequence mutants but not PG independent translocation. Doxorubicin is also shown to bind more efficiently to liposomes containing increased levels of anionic lipid indicating that in these assays it may be inhibiting translocation by preventing electrostatic interaction between the anionic lipid head group and the positively charged signal sequences.

Specific regions of Escherichia coli OmpF protein involved in antigenic and colicin receptor sites and in stable trimerization

Four different mutations were obtained by selecting for resistance to colicin N and screening for continued production of the OmpF protein of Escherichia coli. Two of them also conferred resistance to colicin A. The substitutions C for R-168 (R168C) and E284K caused the loss of the E21 epitope, while the transition G285D altered the E18, E19, and E20 antigenic sites. The substitution G119D drastically affected the stability of the trimeric conformation.

Membrane vesicles containing overproduced SecY and SecE exhibit high translocation ATPase activity and countermovement of protons in a SecA- and presecretory protein-dependent manner

Everted membrane vesicles were prepared from Escherichia coli cells containing either overproduced amounts (OP-membrane vesicles) or normal amounts (normal membrane vesicles) of SecY and SecE, both of which are essential components of the protein translocation apparatus. The rates of translocation of pro-OmpA were similar in the two types of membrane vesicles, whereas translocation ATPase activity, which requires SecA, a precursor protein (pro-OmpA), and membrane vesicles, was appreciably higher with OP-membrane vesicles than with normal membrane vesicles. Since ATP hydrolysis has been shown to take place at an earlier part of the translocation reaction, these results suggest that the overproduction of SecY and SecE enhanced the activity of the earlier process, but not the entire process, of the translocation reaction. The addition of pro-OmpA in the presence of SecA caused the partial collapse of delta pH (inside acidic) generated on OP-membrane vesicles, suggesting that protons come out from the inside of the membrane vesicles in a pro-OmpA-dependent manner. The collapse of delta pH caused by pro-OmpA required SecA, ATP, and SecY and was not detected when normal membrane vesicles were used. These results indicate that the early event of protein translocation, which requires the functioning of SecA, SecY, and SecE, causes the countermovement of protons.

Interleukin-2 enhances the viability of primary cultured rat neocortical neurons

We determined the neurotrophic activity of interleukin-2 (IL-2) on primary cultured neocortical neurons from embryonic rat brain. IL-2 clearly enhanced the viability of cultured neurons in a dose-dependent manner. The neurotrophic effect of IL-2 was completely neutralized by IL-2 antibody. Furthermore, expression of IL-2 receptor mRNA was more pronounced in neurons than in other cultured cells such as astroglia and microglia. These results strongly suggest that IL-2 plays certain roles in the central nervous system as a neurotrophic factor.

Translocation of conjugated presecretory proteins possessing an internal non-peptide domain into everted membrane vesicles in Escherichia coli

Polypeptides comprising 20 amino acid residues (Y2) were covalently bound to the carboxyl terminus of a truncated proOmpA (proOmpA-D72C) through N,N'-bis(3-maleimidopropionyl)-2-hydroxy-1,3-propanediamine (X). The length of the inverted linker domain was 2.8 nm. proOmpA-D72C-X-Y2 thus synthesized was subjected to in vitro translocation into everted membrane vesicles of Escherichia coli. The conjugated protein was translocation-competent in terms of both proteinase K resistance and signal peptide cleavage, when a proton motive force (delta microH+) was imposed. The translocation was ATP-dependent. The proteinase K-treatment resulted in the digestion of SecA, SecE, and SecY in the membrane, suggesting that the proteinase K resistance of the Y2 domain was not due to its interaction with these Sec proteins in the secretory machinery. In the absence of delta microH+, the translocation ceased at the linker domain. Upon the imposition of delta microH+, the linker-Y2 domain underwent translocation, which did not require ATP hydrolysis as in the case of the translocation of the latter portion of usual secretory proteins. The translocation was prevented by anti-Y2 IgG even when delta microH+ was imposed. Another conjugated protein, which possesses a polypeptide comprising 61 amino acid residues after the linker (proOmpA-D72C-X-Lpp'), was synthesized. This compound was also translocated into everted membrane vesicles with cleavage of the signal peptide. These results suggest that substances to be translocated through the secretory machinery need not necessarily be solely held together by polypeptide bonds.

Molecular cloning, sequencing, and mapping of the gene encoding protease I and characterization of proteinase and proteinase-defective Escherichia coli mutants

Clones carrying the gene encoding a proteinase were isolated from Clarke and Carbon's collection, using a chromogenic substrate, N-benzyloxycarbonyl-L-phenylalanine beta-naphthyl ester. The three clones isolated, pLC6-33, pLC13-1, and pLC36-46, shared the same chromosomal DNA region. A 0.9-kb Sau3AI fragment within this region was found to be responsible for the overproduction of the proteinase, and the nucleotide sequence of the region was then determined. The proteinase was purified to homogeneity from the soluble fraction of an overproducing strain possessing the cloned gene. N-terminal amino acid sequencing of the purified protein revealed that the cloned gene is the structural gene for the protein, with the protein being synthesized in precursor form with a signal peptide. On the basis of its molecular mass (20 kDa), periplasmic localization, and substrate specificity, we conclude this protein to be protease I. By using the gene cloned on a plasmid, a deletion mutant was constructed in which the gene was replaced by the kanamycin resistance gene (Kmr) on the chromosome. The Kmr gene was mapped at 11.8 min, the gene order being dnaZ-adk-ush-Kmr-purE, which is consistent with the map position of apeA, the gene encoding protease I in Salmonella typhimurium. Therefore, the gene was named apeA. Deletion of the apeA gene, either with or without deletion of other proteinases (protease IV and aminopeptidase N), did not have any effect on cell growth in the various media tested.

SecD is involved in the release of translocated secretory proteins from the cytoplasmic membrane of Escherichia coli

The SecD protein is one of the components that has been suggested from genetic studies to be involved in the protein secretion across the cytoplasmic membrane of Escherichia coli. We examined the effect of anti-SecD IgG on protein secretion using spheroplasts. Inhibition of the secretion of OmpA and maltose-binding protein (MBP) by this IgG was observed with concomitant accumulation of their precursor and mature forms in spheroplasts. This effect was specific to anti-SecD IgG. Anti-SecE and anti-SecY IgGs, of which the epitopes are located at the periplasmic domains of SecE and SecY, respectively, did not interfere with the secretion. Time-course experiments investigating the processing of proMBP and the release of MBP from spheroplasts revealed that anti-SecD IgG interfered with the release of the translocated mature MBP. The mature form of MBP thus accumulated was sensitive to trypsin, which was externally added to spheroplasts, whereas MBP released into the medium was resistant to trypsin as the native MBP is. The precursor form of MBP accumulated in spheroplasts was also trypsin resistant. We conclude that SecD is directly involved in protein secretion and important for the release of proteins that have been translocated across the cytoplasmic membrane.

Overproduction, purification and characterization of SecD and SecF, integral membrane components of the protein translocation machinery of Escherichia coli

SecD and SecF proteins were overproduced by means of recombinant DNA technology. Immunoblot and amino-acid sequencing analysis revealed that the overproduced proteins are SecD and SecF. The SecD- or SecF-overproduced membrane fraction was subjected to differential solubilization. The SecD protein was then purified through ion-exchange and size-exclusion chromatographies. The SecF protein was purified through size exclusion chromatography. Proteoliposomes reconstituted from the purified SecD and SecF together with SecE and SecY were used to analyze the translocation activity. SecD and SecF did not exhibit significant effects on the translocation activity of proteoliposomes. The amounts of SecD and SecF in overproducers were determined densitometrically on a stained SDS gel and their overproduction (fold) was determined by means of immunoblot analysis. Then the number of these molecules in one normal cell were estimated. From these numbers, together with those of other Sec proteins, the number of the translocation machinery existing in one Escherichia coli cell was inferred to be around 500.

In vivo and in vitro characterization of the secA gene product of Bacillus subtilis

The putative amino acid sequence from the wild-type Bacillus subtilis div+ gene, which complements the temperature-sensitive div-341 mutation, shares a 50% identity with the sequence from Escherichia coli secA (Y. Sadaie, H. Takamatsu, K. Nakamura, and K. Yamane, Gene 98:101-105, 1991). The B. subtilis div-341 mutant accumulated the precursor proteins of alpha-amylase and beta-lactamase at 45 degrees C as in the case of sec mutants of E. coli. The div-341 mutation is a transition mutation causing an amino acid replacement from Pro to Leu at residue 431 of the putative amino acid sequence. The B. subtilis div+ gene was overexpressed in E. coli under the control of the tac promoter, and its product was purified to homogeneity. The Div protein consists of a homodimer of 94-kDa subunits which possesses ATPase activity, and the first 7 amino acids of the putative Div protein were found to be subjected to limited proteolysis in the purified protein. The antiserum against B. subtilis Div weakly cross-reacted with E. coli SecA. On the other hand, B. subtilis Div could not replace E. coli SecA in an E. coli in vitro protein translocation system. The temperature-sensitive growth of the E. coli secA mutant could not be restored by the introduction of B. subtilis div+, which is expressed under the control of the spac-1 promoter, and vice versa. The B. subtilis div+ gene is the B. subtilis counterpart of E. coli secA, and we propose that the div+ gene be referred to as B. subtilis secA, although Div did not function in the protein translocation system of E. coli.

The requirement of a positive charge at the amino terminus can be compensated for by a longer central hydrophobic stretch in the functioning of signal peptides

A variety of model presecretory proteins, proOmpF-Lpps, possessing different numbers of lysine residues (0, 2, and 4) as positively charged amino acid residues and different numbers of leucine residues (7, 8, and 9) as hydrophobic amino acid residues in their signal peptides were constructed. The effect of positive charges on the in vitro translocation efficiency markedly differed with the number of leucine residues. Positive charges were strongly required for translocation when the hydrophobic region comprised 7 or 8 leucine residues, whereas the translocation of proOmpF-Lpps possessing 9 leucine residues took place efficiently even in the absence of positive charges and the introduction of positive charges did not significantly enhance the translocation efficiency. The translocation of all the proOmpF-Lpps, including one possessing no positive charge, was ATP-, protonmotive force-, and SecA-dependent and accompanied by signal peptide cleavage, indicating that they are translocated via the usual secretory pathway. It is likely that the requirement of positive charges can be compensated for by a longer hydrophobic stretch in the functioning of the signal peptide.

Dynamics of the exposure of epitopes on OmpF, an outer membrane protein of Escherichia coli

The OmpF protein is the major outer membrane trimeric porin of Escherichia coli B. The exposure of several cell-surface-exposed epitopes, that are recognized by various monoclonal antibodies directed against the protein, is investigated. Kinetic analyses show that two epitopes (E18 and E19) appear early during the in-vivo assembly on the folded monomer, just after the removal of the signal peptide, and are conserved in the native trimer. The trimerization that immediately follows or occurs in conjunction with the folding of monomers exposes another antigenic site (E21) at the surface of metastable forms. The binding of nascent lipopolysaccharide promotes the conversion of the heat-modifiable intermediate to a stable trimer and ensures the exposure of E20, E1, E3, E4 and E7. Late epitopes, E1, E3, E4 and E7 are only detected in the outer membrane fraction. These results suggest that different steps induce the sequential exposure of native antigenic sites. The detection of these epitopes depends on conformational changes occurring during the OmpF insertion into the outer membrane.

The carboxyl-terminal region of SecE interacts with SecY and is functional in the reconstitution of protein translocation activity in Escherichia coli

Genes encoding the C- and N-terminal regions of SecE were constructed and placed under the control of the tac promoter on plasmids. The C-terminal region of SecE (SecE-C) was sufficient for suppression of the secEcs phenotype, confirming the results of Schatz et al. (Schatz, P. J., Bieker, K. L., Ottemann, K. M., Silhavy, T. J., and Beckwith, J. (1991) EMBO J. 10, 1749-1757). SecE-C allowed the overproduction of SecY, and its overproduction was achieved when the tac-secY gene, on a plasmid, was induced, indicating that the C-terminal region is the site of interaction of SecE with SecY and that the interaction makes the two Sec proteins stable. SecE-C was purified and used with SecY for the reconstitution of protein translocation activity. SecE-C was active in the functional reconstitution. The SecE-C/SecY-dependent protein translocation absolutely required SecA and ATP as the native translocation reaction did. Quantitative analysis revealed that SecE-C was 50% as active as intact SecE. The N-terminal region of SecE (SecE-N) also suppressed in vivo the defect caused by the secEcs mutation. SecE-N was, however, inactive in the overproduction of SecY. A possible oligomeric structure of SecE is discussed.

Nutritional improvement, cardiovascular diseases and longevity in Japan

1. Nutritional conditions have improved remarkably for the past 40 years in Japan; major improvements are increases in protein intake (69.7 in 1955 to 79.2g/day per capita in '88), and fat intake (20.3 in '55 to 58.3 g/day per capita in '88), both of which are significantly related statistically to the gradual reduction of stroke mortality (r = -0.74, not significant; r = -0.78, p < 0.05) and to a remarkable extension of average life span (r = 0.91, p < 0.01; r = 0.98, p < 0.001) in the Japanese. 2. Average heights of 12-year old male and female children, correlating significantly with these nutritional improvements, are significantly positively correlated with average life spans (men and women respectively; r = 0.97, p < 0.001). 3. Thus, general nutritional improvements among the Japanese are regarded as the major contributory factor to the recent achievement of top-ranked position for longevity in the world.

International cooperative study on the relationship between dietary factors and blood pressure: a preliminary report from the Cardiovascular Diseases and Alimentary Comparison (CARDIAC) Study. The CARDIAC Cooperative Study Research Group

1. To investigate the epidemiological relationship of dietary factors to blood pressure (BP) and major cardiovascular diseases, we carried out the international cooperative Cardiovascular Diseases and Alimentary Comparison (CARDIAC) Study, which so far involves 48 centers in 20 countries as of August 1991. From each population, 100 men and 100 women aged 50-54 years were randomly selected for BP measurement, 24-h urine collection, blood tests, and medical interview. Various biological markers of diets from urine and blood were analyzed centrally in the Izumo CARDIAC center. 2. Cross center analysis using simple linear regression revealed strong significant correlations of body mass index (BMI) to systolic BP (SBP; p < 0.01) and diastolic BP (DBP; p < 0.001) in men. 24-h urinary sodium (Na) excretion in men also showed significant correlations with SBP (p < 0.05) and DBP p < 0.05) even after controlling for the effect of BMI (SBP; p < 0.05, DBP; p < 0.05). 3. Within center analysis using multiple linear regression implied that BMI and Na strongly adversely affect BP, whereas magnesium may have beneficial influence on BP. 4. Multicolinearities among 24h urinary sodium, calcium, and urea nitrogen were noted in men.

Effects of total hydrophobicity and length of the hydrophobic domain of a signal peptide on in vitro translocation efficiency

The hydrophobic domain of the signal peptide of OmpF-Lpp, a model secretory protein, was systematically engineered so as to be composed of different lengths of polyleucine residues or polymers with alternate leucine and alanine residues, and the effects of the length and nature of the hydrophobic stretch on the rate of in vitro translocation were studied using everted membrane vesicles of Escherichia coli. The translocation reaction exhibited high substrate specificity as to the number of hydrophobic residues. The results suggest that the hydrophobic domain is recognized specifically by a component(s) of the secretory machinery rather than nonspecifically by the hydrophobic region of the membrane. The in vitro translocation thus demonstrated required SecA and ATP and was markedly enhanced upon imposition of the proton motive force, as in the case of secretory proteins possessing a natural signal peptide. The highest translocation rate was obtained with the octamer in the case of polyleucine-containing signal peptides, whereas it was the decamer in the case of ones containing both leucine and alanine. These results suggest that the total hydrophobicity of the hydrophobic region of the signal peptides is an important determinant of the substrate specificity.

SecY, SecE, and band 1 form the membrane-embedded domain of Escherichia coli preprotein translocase

The preprotein translocase of Escherichia coli is a multisubunit enzyme with two domains, the peripheral membrane protein SecA and the membrane-embedded SecY/E protein. SecY/E has been isolated as a complex of three polypeptides, SecY, SecE, and band 1. We now present four lines of evidence that the active species of SecY/E is composed of a tightly associated complex of these three subunits: 1) antibodies to SecY efficiently precipitate SecY/E activity as well as all three polypeptides; 2) the proportions of SecY, SecE, and band 1 in the immunoprecipitates are the same as in the starting fraction; 3) the immunoprecipitable complex is not disrupted by treatment with either high salt or urea but is disrupted by brief incubation at 20 degrees C, and the kinetics of dissociation of both band 1 and SecE from SecY at 20 degrees C parallel the loss of translocation ATPase activity; 4) upon immunoprecipitation of similar units of activity of translocase from detergent solutions from either wild-type membranes or a SecY and SecE overproducer strain, the SecE and band 1 subunits are recovered in the same proportions. These data establish that the subunits of SecY/E are firmly associated and that it is the associated complex which is active for translocation.

Neutrophil chemotactic factors produced by a cell line from thyroid carcinoma

A neutrophil chemotactic factor (human interleukin 8, human granulocyte-macrophage colony-stimulating factor)-producing cell line, named KHM-5M, was established from a patient with an undifferentiated thyroid carcinoma, neutrophilia, and malignant pleurisy with many neutrophils and a few malignant cells. The cell line was transplanted into nude rats, and the infiltration of neutrophils was observed in and around the transplanted tumor tissue. Neutrophil chemotactic activity was predicted from the clinical features and pathological findings in this case. The extreme chemotactic activity of the neutrophils was demonstrated in conditioned medium from KHM-5M cells using the modified Boyden chamber technique. With sodium dodecyl sulfate-polyacrylamide gel electrophoresis, at least two neutrophil chemotactic activities in conditioned medium from the cell line were observed. The levels of these activities derived from KHM-5M cells were screened by measuring conditioned medium from the COS cells, which expressed a complementary DNA library from the KHM-5M cells. Chemotactic activities (human interleukin 8, human granulocyte-macrophage colony-stimulating factor) were identified by DNA cloning. These results show that the KHM-5M cells derived from an undifferentiated thyroid carcinoma produce multicytokines and suggest that those cytokines modified some pathological features in this case.

In vitro translocation of secretory proteins possessing no charges at the mature domain takes place efficiently in a protonmotive force-dependent manner

The effect of charges existing on the mature domain of secretory proteins on the efficiency and protonmotive force dependence of translocation into everted membrane vesicles of Escherichia coli was studied. Model secretory proteins devoid of charges on the mature domain were constructed at the DNA level using proOmpF-Lpp as the starting protein. The chargeless presecretory proteins thus constructed were translocated and processed for the signal peptide much faster than proOmpF-Lpp and the rate of translocation was appreciably enhanced by imposition of the protonmotive force. Not only the membrane potential but also delta pH were effective in stimulating the rate of translocation of the chargeless proteins. The results indicate that the mature domain does not have to be charged for the secretory translocation and that the major requirement of the protonmotive force for the secretory translocation is not for the movement, including an electrophoretic one, of charged regions of the mature domain. All of the proOmpF-Lpp derivatives thus constructed were translocated efficiently into everted membrane vesicles in a SecA-dependent manner, irrespective of their size. The mature domain of the smallest one was 45 amino acid residues in length. Contrary to the views previously presented by other workers, these results suggest that there is no sharp boundary at the reported regions for the translocation of presecretory proteins across the cytoplasmic membrane or for the requirement of SecA.