Glucose and cAMP regulate the L-type pyruvate kinase gene by phosphorylation/dephosphorylation of the carbohydrate response element binding protein.

Recently we purified and identified a previously uncharacterized transcription factor from rat liver binding to the carbohydrate responsive element of the L-type pyruvate kinase (L-PK) gene. This factor was named carbohydrate responsive element binding protein (ChREBP). ChREBP, essential for L-PK gene transcription, is activated by high glucose and inhibited by cAMP. Here, we demonstrated that (i) nuclear localization signal and basic helix-loop-helix/leucine-zipper domains of ChREBP were essential for the transcription, and (ii) these domains were the targets of regulation by cAMP and glucose. Among three cAMP-dependent protein kinase phosphorylation sites, Ser(196) and Thr(666) were the target sites. Phosphorylation of the former resulted in inactivation of nuclear import, and that of the latter resulted in loss of the DNA-binding activity and L-PK transcription. On the other hand, glucose activated the nuclear import by dephosphorylation of Ser(196) in the cytoplasm and also stimulated the DNA-binding activity by dephosphorylation of Thr(666) in the nucleus. These results thus reveal mechanisms for regulation of ChREBP and the L-PK transcription by excess carbohydrate and cAMP.

Enhancement of the thermal stability of pyroglutamyl peptidase I by introduction of an intersubunit disulfide bond.

From the comparison of the three-dimensional structure of mesophilic pyroglutamyl peptidase from Bacillus amyloliquefaciens and the thermophilic enzyme from Thermococcus litoralis, the intersubunit disulfide bond was estimated to be one of the factors for thermal stability. Since Ser185 was corresponded to Cys190 of the thermophilic enzyme by sequence alignment, the Ser185 residue was replaced with cysteine by site-directed mutagenesis. The S185C mutant enzyme appeared to form a disulfide bond, which was confirmed by SDS-PAGE with and without 2-mercaptoethanol. The mutant enzyme showed a catalytic efficiency equivalent to that of the wild-type enzyme for hydrolysis of a synthetic peptide substrate. However, the thermal stability of the S185C mutant was found to be 30 degrees C higher than that of wild-type. Thus the introduction of a disulfide bond enhanced thermal stability without changing the catalytic efficiency of the enzyme.

Substrate recognition mechanism of prolyl aminopeptidase from Serratia marcescens.

Molecular cloning of the gene and the crystal structure of the prolyl aminopeptidase [EC 3.4.11.5] from Serratia marcescens have been studied by us [J. Biochem. 122, 601-605 (1997); ibid. 126, 559-565 (1999)]. Through these studies, Phe139, Tyr149, Glu204, and Arg136 were estimated to be concerned with substrate recognition. To elucidate the details of the mechanism for the substrate specificity, the site-directed mutagenesis method was applied. The F139A mutant showed an 80-fold decrease in catalytic efficiency (k(cat)/K(m)), but the Y149A mutant did not show a significant change in catalytic efficiency. The catalytic efficiency of the E204Q mutant was about 4% of that of the wild type. The peptidase activity of the mutant (R136A) was markedly decreased, however, arylamidase activity with Pyr-bNA was retained as in the wild-enzyme. From these results, it was clarified that the pyrrolidine ring and the amino group of proline at the S1 site were recognized by Phe139 and Glu204, respectively. P1' of a substrate was recognized by Arg136. On the other hand, the enzyme had two cysteine residues. Mutants C74A and C271A were inhibited by PCMB, but the double mutated enzyme (C74/271A) was resistant to it.

Glutamate 83 is important for stabilization of domain-domain conformation of Thermus aquaticus glycerol kinase.

The gene glpK, encoding glycerol kinase (GlpK) of Thermus aquaticus, has recently been identified. The protein encoded by glpK was found to have an unusually high identity of 81% with the sequence of GlpK from Bacillus subtilis. Three residues (Arg-82, Glu-83, and Asp-244) of T. aquaticus GlpK are conserved in all the known GlpK sequences, including those from various bacteria, yeast and human. The roles that these three residues play in the catalytic mechanism were investigated by using site-directed mutagenesis to produce three mutants: Arg-82-Ala, Glu-83-Ala, and Asp-244-Ala. Replacement of Asp-244 by Ala resulted in a complete loss of activity, thus suggesting that Asp-244 is important for catalysis. Taking k(cat)/K(m) as a simple measure of catalytic efficiency, the mutants Arg-82-Ala and Glu-83-Ala were judged to cause 190- and 37,000-fold decrease, respectively, when compared to the wild-type GlpK. Thus, these three residues play a critical role in the catalytic mechanism. However, only mutant Glu-83-Ala was cleaved by alpha-chymotrypsin, and proteolysis studies showed that the mutant Glu-83-Ala involves a change in the exposure of Tyr-331 at the alpha-chymotrypsin site. This indicates a large domain conformational change, since the residues corresponding to Glu-83 and Tyr-331 in the Escherichia coli GlpK sequence are located in domain IB and domain IIB, respectively. The apparent conformational change caused by replacement of Glu-83 leads us to propose that Glu-83 is an important residue for stabilization of domain conformation.

[Psychological characteristics of unsuccessful pilot trainees].

Some pilot trainees can not pass flight examinations and are obliged to give up their flight training because of their insufficient technical skills. We investigated their results of group Rorschach test (a multiple-choice test with ink blots which are similar to those for face-to-face Rorschach test). Subjects were 20 male pilot trainees (F (fail) group: mean age 22.6 +/- 1.5 years) who were obliged to give up their flight trainings between 1985 and 1996 because of their insufficient technical skills. The control group was made up of 125 male pilot trainees (P (pass) group: mean age 22.4 +/- 1.7 years) who were the successful classmates of the unsuccessful trainees. We investigated the differences of the results of group Rorschach test given for employment screening between the two groups. All results of the scores in group Rorschach test were within normal limits both in P group and F group. There, however, were following significant differences between the two groups: (1) F group showed more Key- responses than P group (F group: 4.9 +/- 2.1 P group: 3.4 +/- 2.0, p<0.01). (2) F group showed more k responses than P group (F group: 0.2 +/- 0.4 P group: 0.02 +/- 0.1, p<0.01). (3) P group showed more FC' responses than F group (F group: 1.4 +/- 1.0 P group: 2.2 +/- 1.2, p<0.01). (4) F group showed more cF responses than P group (F group: 1.6 +/- 1.2 P group: 1.0 +/- 0.9, p<0.05). (5) P group showed higher form level than F group (F group: 120.6 +/- 15.8 P group: 128.2 +/- 12.6, p<0.05). The pilot trainees in F group were suggested to have vulnerability to be nervous and anxious in an inexperienced situation, to decline their ability to cope objectively and effectively with a new situation, and to increase desire for dependence upon others.

Crystal structure of prolyl aminopeptidase from Serratia marcescens.

Prolyl aminopeptidase from Serratia marcescens specifically catalyzes the removal of N-terminal proline residues from peptides. We have solved its three-dimensional structure at 2.3 A resolution by the multiple isomorphous replacement method. The enzyme consists of two contiguous domains. The larger domain shows the general topology of the alpha/beta hydrolase fold, with a central eight-stranded beta-sheet and six helices. The smaller domain consists of six helices. The catalytic triad (Ser113, His296, and Asp268) is located near the large cavity at the interface between the two domains. Cys271, which is sensitive to SH reagents, is located near the catalytic residues, in spite of the fact that the enzyme is a serine peptidase. The specific residues which make up the hydrophobic pocket line the smaller domain, and the specificity of the exo-type enzyme originates from this smaller domain, which blocks the N-terminal of P1 proline.

The crystal structure of pyroglutamyl peptidase I from Bacillus amyloliquefaciens reveals a new structure for a cysteine protease.

BACKGROUND: The N-terminal pyroglutamyl (pGlu) residue of peptide hormones, such as thyrotropin-releasing hormone (TRH) and luteinizing hormone releasing hormone (LH-RH), confers resistance to proteolysis by conventional aminopeptidases. Specialized pyroglutamyl peptidases (PGPs) are able to cleave an N-terminal pyroglutamyl residue and thus control hormonal signals. Until now, no direct or homology-based three-dimensional structure was available for any PGP. RESULTS: The crystal structure of pyroglutamyl peptidase I (PGP-I) from Bacillus amyloliquefaciens has been determined to 1.6 A resolution. The crystallographic asymmetric unit of PGP-I is a tetramer of four identical monomers related by noncrystallographic 222 symmetry. The protein folds into an alpha/beta globular domain with a hydrophobic core consisting of a twisted beta sheet surrounded by five alpha helices. The structure allows the function of most of the conserved residues in the PGP-I family to be identified. The catalytic triad comprises Cys144, His168 and Glu81. CONCLUSIONS: The catalytic site does not have a conventional oxyanion hole, although Cys144, the sidechain of Arg91 and the dipole of an alpha helix could all stabilize a negative charge. The catalytic site has an S1 pocket lined with conserved hydrophobic residues to accommodate the pyroglutamyl residue. Aside from the S1 pocket, there is no clearly defined mainchain substrate-binding region, consistent with the lack of substrate specificity. Although the overall structure of PGP-I resembles some other alpha/beta twisted open-sheet structures, such as purine nucleoside phosphorylase and cutinase, there are important differences in the location and organization of the active-site residues. Thus, PGP-I belongs to a new family of cysteine proteases.

Cloning of a novel prolidase gene from Aureobacterium esteraromaticum.

The prolidase gene from Aureobacterium esteraromaticum was cloned and expressed in Escherichia coli. The cloned enzyme had the same enzymatic properties as the wild-type enzyme. Kinetic analysis of the enzyme indicated that the best substrate was Pro-Hyp, which was not hydrolyzed by other prolidases. Interestingly, there was no homology between the deduced amino acid sequence of A. esteraromaticum prolidase and those of the other sources such as human E. coli and Lactobacillus. However, homology was seen with the yeast hypothetical protein YJL213w, the function of which is unknown. These findings indicate that the A. esteraromaticum prolidase is a novel enzyme different from other prolidases reported to date.

Roles of the Ser146, Tyr159, and Lys163 residues in the catalytic action of 7alpha-hydroxysteroid dehydrogenase from Escherichia coli.

The Escherichia coli 7alpha-hydroxysteroid dehydrogenase (7alpha-HSDH; EC 1.1.1.159) has been the subject of our studies, including the cloning of its gene, and determination of the crystal structures of its binary and ternary complexes [J. Bacteriol. 173, 2173-2179 (1991); Biochemistry 35, 7715-7730 (1996)]. Through these studies, the Ser146, Tyr159, and Lys163 residues were found to be involved in its catalytic action. In order to clarify the roles of these residues, we constructed six single mutants of 7alpha-HSDH, Tyr159-Phe (Y159F), Tyr159-His (Y159H), Lys163-Arg (K163R), Lys163-Ile (K163I), Ser146-Ala (S146A), and Ser146-His (S146H), by site-directed mutagenesis. These mutants were overexpressed in E. coli WSD, which is a 7alpha-HSDH null strain, and the expressed enzymes were purified to homogeneity. The kinetic constants of the mutant enzymes were determined, and the structures of the Y159F, Y159H, and K163R mutants were analyzed by X-ray crystallography. The Y159F mutant showed no activity, while the Y159H mutant exhibited 13.3% of the wild-type enzyme activity. No remarkable conformational change between the Y159F (or Y159H) and wild-type proteins was detected on X-ray crystallography. On the other hand, the K163I mutant showed just 5.3% of the native enzyme activity, with a 8. 5-fold higher Kd. However, the K163R mutant retained 64% activity, and no remarkable conformational change was detected on X-ray crystallography. In the cases of the S146A and S146H mutants, the activities fairly decreased, with 20.3 and 35.6% of kcat of the wild-type, respectively. The data presented in this paper confirm that Tyr159 acts as a basic catalyst, that Lys163 binds to NAD(H) and lowers the pKa value of Tyr159, and that Ser146 stabilizes the substrate, reaction intermediate and product in catalysis.

Prolyl endopeptidase from Sphingomonas capsulata: isolation and characterization of the enzyme and nucleotide sequence of the gene.

Prolyl endopeptidase (prolyl oligopeptidase, EC 3.4.21.26) was purified from Sphingomonas capsulata IFO 12533, and its gene was cloned and expressed in Escherichia coli. The recombinant enzyme was markedly inhibited by diisopropyl phosphofluoridate and hardly affected by SH reagents or metal chelators, similar to the native enzyme purified from S. capsulata. Nucleotide sequencing analysis revealed an open reading frame of 2169 bp, coding for a protein of 723 amino acids with a predicted molecular weight of 78,433. The amino acid sequence was 39.6, 45.3, 38.9, and 38.3% homologous to Flavobacterium meningosepticum, Aeromonas hydrophila, porcine brain, and human T cell prolyl endopeptidase, respectively. A region near the C-terminus and the region containing the putative catalytic triad residues were highly conserved. The enzyme was crystallized by the hanging drop vapor diffusion method, using ammonium sulfate as a precipitant.

Thermostable glycerol kinase from Thermus flavus: cloning, sequencing, and expression of the enzyme gene.

The thermostable glycerol kinase (EC 2.7.1.30) gene from Thermus flavus was cloned and expressed in Escherichia coli DH5 alpha. An open reading frame of 1488 bp for the glycerol kinase gene (glpK) starting with an ATG methionine codon was found, which encodes a protein of 496 amino acid residues whose calculated molecular weight is 54,835. The amino acid sequence of T. flavus glycerol kinase is 80.6% and 64.1% identical with those of Bacillus subtilis and E. coli. Transformants of E. coli DH5 alpha harboring plasmid pGYK12 with a 1505 bp chromosomal DNA fragment containing the T. flavus glycerol kinase gene showed about 23.8-fold higher glycerol kinase activity than T. flavus.

Cloning, sequencing, high expression, and crystallization of the thermophile Thermus aquaticus glycerol kinase.

Glycerol kinase (EC 2.7.1.30) is a key enzyme of glycerol uptake and metabolism in bacteria. Using PCR, we amplified and cloned a glycerol kinase gene, glpK, from Thermus aquaticus. The complete gene has 1488 base pairs, coding for a protein of 496 amino acids with a predicted molecular weight of 54,814. The amino acid sequence deduced from T. aquaticus glpK was found to have identities of 97 and 81%, respectively, with those of Thermus flavus and Bacillus subtilis glpK genes. After overproduction in Escherichia coli, the expressed enzyme was easily purified to homogeneity by DEAE-Toyopearl chromatography. The purified enzyme has been crystallized by the hanging drop vapor diffusion method at 22 degrees C. Comparison of the amino acid sequence with that of the B. subtilis enzyme showed that Ser and Lys are replaced by Ala and Arg, as was seen in mesophile and thermophile enzymes.

Prolyl aminopeptidase from Serratia marcescens: cloning of the enzyme gene and crystallization of the expressed enzyme.

We cloned and sequenced the Serratia marcescens prolyl aminopeptidase (SPAP) gene. Nucleotide sequence analysis revealed an open reading frame of 951 bp, encoding a protein of 317 amino acids with a predicted molecular weight of 36,083. The expressed enzyme was purified about 90-fold on columns of Toyopearl HW65C and DEAE-Toyopearl, with an activity recovery of 30%. The apparent molecular weight of the purified enzyme was 36,000 and 38,000 as estimated by SDS-PAGE and gel filtration, respectively. The enzyme was not inhibited by diisopropyl phosphofluoridate (DFP) or phenylmethylsulfonyl fluoride (PMSF), but was markedly inhibited by 3,4-dichloroisocoumarin (DCIC). Crystals of the enzyme were grown by the hanging drop vapor diffusion method using PEG6000 as a precipitant at pH 6.5. The crystals are tetragonal with cell dimensions a= b =65.6 A, and c=169.8 A, a space group P4(1)2(1)2 or P4(3)2(1)2, and probably contain one monomer in the asymmetric unit. They diffract to at least 2.22 A resolution.

Cloning and expression of the cDNA encoding prolyl oligopeptidase (prolyl endopeptidase) from bovine brain.

Prolyl oligopeptidase (EC 3.4.21.26, prolyl endopeptidase) cDNA from bovine brain was cloned by PCR, and the amplified fragment was used as a probe to screen the cDNA library from bovine brain. The obtained clone contained a 2.7 kb DNA fragment with an open reading frame of 2130 nucleotides, and encoded a protein of 710 amino acids with a deduced molecular weight of 80640 Da. The deduced amino acid sequence is 95, 94, 51 and 48% homologous to those of human T-cell, porcine brain, Aeromonas hydrophila, and Flavobacterium meningosepticum prolyl endopeptidases, respectively. The bovine brain prolyl endopeptidase-encoding cDNA was expressed using an expression vector bearing a tac promoter, with an approximate yield of 20 micrograms/ml of cell culture.

Prolyl aminopeptidase gene from Flavobacterium meningosepticum: cloning, purification of the expressed enzyme, and analysis of its sequence.

In spite of the numerous studies regarding prolyl aminopeptidase, little is known about its mechanism and the significance of its similarity to a number of hydrolases of diverse specificity that belong to the alpha/beta hydrolase-fold family (Pseudomonas 2-hydroxymuconic semialdehyde hydrolase, atropinesterase, and 2-hydroxy-6-oxophenylhexa-2,4-dienoic acid hydrolase; human and rat epoxide hydrolases). We report the cloning and sequencing of the novel prolyl aminopeptidase gene from Flavobacterium meningosepticum (FPAP) which allowed a more comprehensive sequence comparison. FPAP was found to be a 35-kDa monomeric enzyme, releasing N-terminal proline but not hydroxyproline residues from small peptides and naphthylamide esters. Using the unweighted pair group method with arithmetic mean method, an evolutionary tree that depicts the probable relationship between the prolyl aminopeptidases and the alpha/beta hydrolase-fold enzymes was constructed. Since the alpha/beta hydrolase-fold family might also include the members of the prolyl oligopeptidase family (prolyl oligopeptidase, dipeptidyl peptidase IV, and prolyl carboxypeptidase), this proposal links all the known Pro-Y bond-cleaving proline-specific peptidases (prolyl oligopeptidase family, prolyl aminopeptidases, and prolinase) as enzymes with similar scaffolds and hydrolytic mechanisms. On the other hand, the enzymes that cleave X-Pro bonds are metalloenzymes grouped within the "pita-bread" fold family (aminopeptidase P and prolidase). Although the latter two enzymes show significant sequence homology, prolyl aminopeptidase, prolinase, and the members of the prolyl oligopeptidase family do not, and might share the alpha/beta hydrolase-fold scaffold. This rationale would explain the failure in finding a common "proline-recognizing motif" in the primary structures of these proline-specific peptidases.

Dipeptidyl peptidase IV from Xanthomonas maltophilia: sequencing and expression of the enzyme gene and characterization of the expressed enzyme.

The dipeptidyl peptidase IV [EC 3.4.14.5] gene of Xanthomonas maltophilia, expressed in Escherichia coli, was cloned by the shotgun method. Nucleotide sequence analysis revealed an open reading frame of 2,223 bp, coding for a protein of 741 amino acids with a predicted molecular weight of 82,080. The expressed enzyme was extracted with SDS, and the solubilized enzyme was purified about 1,030-fold on columns of Toyopearl HW65C, DEAE-Toyopearl twice, and hydroxyapatite, with an activity recovery of 50%. The enzyme hydrolyzed a proline-containing peptide at the penultimate position, and was inhibited by diisopropyl phosphofluoridate. The enzyme was most active at pH 8.5, and was stable between at pH 7.0 and 9.0. The molecular weight of the purified enzyme was estimated to be 83,000 and 165,000 by SDS-PAGE and gel filtration, respectively.

Prolyl aminopeptidase is also present in Enterobacteriaceae: cloning and sequencing of the Hafnia alvei enzyme-gene and characterization of the expressed enzyme.

The Hafnia alvei prolyl aminopeptidase gene (hpap) was cloned and sequenced, the expressed enzyme (HPAP) was purified to homogeneity and thoroughly characterized. An open reading frame of 1,281 bp was found to code for the enzyme, resulting in a protein of 427 amino acids with a molecular weight of 48,577. HPAP resembles the Aeromonas sobria enzyme, having 45% identity and the same distinctive properties with respect to size and substrate specificities. Both enzyme show similar chromatographic behavior, and HPAP could be purified following the procedure previously described for the Aeromonas enzyme. HPAP was found to be resistant to diisopropylphosphofluoridate as are most of the prolyl aminopeptidases hitherto described. In spite of this similarity, no inhibition by 1 mM p-chloromercuribenzoate solution could be detected. Significant inhibition was, however, observed when the enzyme was incubated with 3,4-dichloroisocoumarin. This study confirms the presence of two types of prolyl aminopeptidases, of which the Hafnia and Aeromonas enzymes constitute one group and the Bacillus, Neisseria, and Lactobacillus enzymes the other, and describes the cloning of the first prolyl aminopeptidase gene from an Enterobacteriaceae.

Prolidase from Xanthomonas maltophilia: purification and characterization of the enzyme.

Prolidase (iminodipeptidase, EC 3.4.13.9) was purified from an extract of Xanthomonas maltophilia, by ammonium sulfate fractionation and sequential chromatographies on DEAE-Toyopearl, Toyopearl HW65C, FPLC-Hiload Superdex 200 pg, and FPLC-Hitrap Q columns, which an activity recovery of 2.3%. The enzyme was the most active at pH 7.5 with Leu-Pro as substrate. It was stable between pH 6.0 and 8.5 for 60 min at 37 degrees C and retained half of activity after 60 min at 37 degrees C. The isoelectric point of the enzyme was 3.7. Its molecular weight was estimated to be 100,000 by gel filtration on FPLC-Hiload Superdex 200 and 51,000 by SDS-PAGE, suggesting that it is a dimer. It hydrolyzed dipeptides only if proline is located at the carboxyl terminal position. The enzyme was inhibited by PCMB and o-phenanthroline, and was activated by Mn2+.

Cloning, sequencing, and expression of the dipeptidyl peptidase IV gene from Flavobacterium meningosepticum in Escherichia coli.

The dipeptidyl peptidase IV (DP IV, EC 3.4.14.5) gene from Flavobacterium meningosepticum was cloned by Southern and colony hybridizations using probes amplified by PCR, and expressed in Escherichia coli DH1. E. coli DH1 harboring pFDP-H1, which was a subclone derived from the positive clone pFDP-1, showed 3.5-fold higher activity than F. meningosepticum. Nucleotide sequencing analysis revealed an open reading frame of 2133 bp, coding for a protein of 711 amino acids with a predicted molecular weight of 80,626. The expressed enzyme in E. coli DH1/pFDP-H1 was purified about 345-fold with an activity recovery of 12.3%. The molecular weight of the purified enzyme was estimated to be 75,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and 160,000 by gel filtration, respectively, suggesting a dimeric form of the native enzyme. The deduced amino acid sequence of DP IV was homologous to those of the serine proteases of the "prolyl endopeptidase family." A sequence near the C-terminal region and the putative catalytic triad residues were well conserved among these enzymes.