A novel membrane protein that is transported to protein storage vacuoles via precursor-accumulating vesicles.

A novel protein, MP73, was specifically found on the membrane of protein storage vacuoles of pumpkin seed. MP73 appeared during seed maturation and disappeared rapidly after seed germination, in association with the morphological changes of the protein storage vacuoles. The MP73 precursor deduced from the isolated cDNA was composed of a signal peptide, a 24-kD domain (P24), and the MP73 domain with a putative long alpha-helix of 13 repeats that are rich in glutamic acid and arginine residues. Immunocytochemistry and immunoblot analysis showed that the precursor-accumulating (PAC) vesicles (endoplasmic reticulum-derived vesicles responsible for the transport of storage proteins) accumulated proMP73, but not MP73, on the membranes. Subcellular fractionation of the pulse-labeled maturing seed demonstrated that the proMP73 form with N-linked oligosaccharides was synthesized on the endoplasmic reticulum and then transported to the protein storage vacuoles via PAC vesicles. Tunicamycin treatment of the seed resulted in the efficient deposition of proMP73 lacking the oligosaccharides (proMP73 Delta Psi) into the PAC vesicles but no accumulation of MP73 in vacuoles. Tunicamycin might impede the transport of proMP73 Delta Psi from the PAC vesicles to the vacuoles or might make the unglycosylated protein unstable in the vacuoles. After arrival at protein storage vacuoles, proMP73 was cleaved by the action of a vacuolar enzyme to form a 100-kD complex on the vacuolar membranes. These results suggest that PAC vesicles might mediate the delivery of not only storage proteins but also membrane proteins of the vacuoles.

Chloroplasts have a novel Cpn10 in addition to Cpn20 as co-chaperonins in Arabidopsis thaliana.

Previously, we characterized a mitochondrial co-chaperonin (Cpn10) and a chloroplast co-chaperonin (Cpn20) from Arabidopsis thaliana (Koumoto, Y., Tsugeki, R., Shimada, T., Mori, H., Kondo, M., Hara-Nishimura, I., and Nishimura, M. (1996) Plant J. 10, 1119-1125; Koumoto, Y., Shimada, T., Kondo, M., Takao, T., Shimonishi, Y., Hara-Nishimura, I., and Nishimura, M. (1999) Plant J. 17, 467-477). Here, we report a third co-chaperonin. The cDNA was 603 base pairs long, encoding a protein of 139 amino acids. From a sequence analysis, the protein was predicted to have one Cpn10 domain with an amino-terminal extension that might work as a chloroplast transit peptide. This novel Cpn10 was confirmed to be localized in chloroplasts, and we refer to it as chloroplast Cpn10 (chl-Cpn10). The phylogenic tree that was generated with amino acid sequences of other co-chaperonins indicates that chl-Cpn10 is highly divergent from the others. In the GroEL-assisted protein folding assay, about 30% of the substrates were refolded with chl-Cpn10, indicating that chl-Cpn10 works as a co-chaperonin. A Northern blot analysis revealed that mRNA for chl-Cpn10 is accumulated in the leaves and stems, but not in the roots. In germinating cotyledons, the accumulation of chl-Cpn10 was similar to that of chloroplastic proteins and accelerated by light. It was proposed that two kinds of co-chaperonins, Cpn20 and chl-Cpn10, work independently in the chloroplast.

The transition state in the folding-unfolding reaction of four species of three-disulfide variant of hen lysozyme: the role of each disulfide bridge.

The effects of lacking a specific disulfide bridge on the transition state in folding were examined in order to explore the folding-unfolding mechanism of lysozyme. Four species of three-disulfide variant of hen lysozyme (3SS-lysozyme) were prepared by replacing two Cys residues with Ala or Ser: C6S/C127A, C30A/C115A, C64A/C80A and C76A/C94A. The recombinant hen lysozyme was studied as the standard reference containing four authentic disulfide bridges and the extra N-terminal Met: the recombinant hen lysozyme containing the extra N-terminal. Folding rates were measured by monitoring the change in fluorescence intensity associated with tri-N-acetyl-d-glucosamine binding to the active site of refolded lysozyme. It was confirmed that the folding rate of the recombinant hen lysozyme containing the extra N-terminal was the same as that of wild-type lysozyme, and that the folding rate was little affected by the presence of tri-N-acetyl-d-glucosamine (triNAG). The folding rate of C64A/C80A was found to be the fastest and almost the same as that of the recombinant hen lysozyme containing the extra N-terminal, and that of C30A/C115A the second, and that of C6S/C127A the third. The folding rate of C76A/C94A was particularly slow. On the other hand, the unfolding rates which were measured in the presence of triNAG showed the dependence on the concentration of triNAG. The intrinsic unfolding rate in the absence of triNAG was determined by extrapolation. Also in the unfolding rate, C76A/C94A was markedly slower than the others. It was found from the analysis of binding constants of triNAG to C64A/C80A during the unfolding process that the active site of C64A/C80A partly unfolds already prior to the unfolding transition. On the basis of these kinetic data, we suggest that C64A/C80A folding transition can occur with leaving the loop region around SS3 (C64-C80) flexible, while cross-linking by SS4 (C76-C94) is important for the promotion of folding, because it is an indispensable constraint on the way towards the folding transition state.

Chloroplast Cpn20 forms a tetrameric structure in Arabidopsis thaliana.

Chloroplast chaperonin 20 (Cpn20) in higher plants is a functional homologue of the Escherichia coli GroES, which is a critical regulator of chaperonin-mediated protein folding. The cDNA for a Cpn20 homologue of Arabidopsis thaliana was isolated. It was 958 bp long, encoding a protein of 253 amino acids. The protein was composed of an N-terminal chloroplast transit peptide, and the predicted mature region comprised two distinct GroES domains that showed 42% amino acid identity to each other. The isolated cDNA was constitutively expressed in transgenic tobacco. Immunogold labelling showed that Cpn20 is accumulated in chloroplasts of transgenic tobacco. A Northern blot analysis revealed that mRNA for the chloroplast Cpn20 is abundant in leaves and is increased by heat treatment. To examine the oligomeric structure of Cpn20, a histidine-tagged construct lacking the transit peptide was expressed in E. coli and purified by affinity chromatography. Gel-filtration and cross-linking analyses showed that the expressed products formed a tetramer. The expressed products could substitute for GroES to assist the refolding of citrate synthase under non-permissive conditions. The analysis on the subunit stoichiometry of the GroEL-Cpn20 complex also revealed that the functional complex is composed of a GroEL tetradecamer and a Cpn20 tetramer.

Isolation and characterization of a cDNA encoding mitochondrial chaperonin 10 from Arabidopsis thaliana by functional complementation of an Escherichia coli groES mutant.

Chaperonin (Cpn) is one of the molecular chaperones. Cpn10 is a co-factor of Cpn60, which regulates Cpn60-mediated protein folding. It is known that Cpn10 is located in mitochondria and chloroplasts in plant cells. The Escherichia coli homologue of Cpn10 is called GroES. A cDNA for the Cpn10 homologue was isolated from Arabidopsis thaliana by functional complementation of the E. coli groES mutant. The cDNA was 647 bp long and encoded a polypeptide of 98 amino acids. The deduced amino acid sequence showed approximately 50% identity to mammalian mitochondrial Cpn10s and 30% identity to GroES. A Northern blot analysis revealed that the mRNA for the Cpn10 homologue was expressed uniformly in various organs and was markedly induced by heat-shock treatment. The Cpn10 homologue was constitutively expressed in transgenic tobaccos. Immunogold and immunoblot analyses following the subcellular fractionation of leaves from transgenic tobaccos revealed that the Cpn 10 homologue was localized in mitochondria and accumulated at a high level in transgenic tobaccos.

Relationship between the optimal temperature for oxidative refolding and the thermal stability of refolded state of hen lysozyme three-disulfide derivatives.

The temperature dependence of the efficiency of oxidative refolding was examined for hen lysozyme three-disulfide derivatives produced in Escherichia coli. Each derivative was designed to lack one of the four disulfide bridges in authentic lysozyme: delta 1 (Cys6-->Ser, Cys127-->Ser), delta 2 (Cys30-->Ser, Cys115-->Ser), delta 3 (Cys64-->Ser, Cys80-->Ser), delta 4 (Cys76-->Ser, Cys94-->Ser), delta 2Ala (Cys30-->Ala, Cys115-->Ala), and delta 4Ala (Cys76-->Ala, Cys94-->Ala). The optimal refolding temperature was lowest for delta 1 (19 degrees C) and highest for delta 4Ala (30 degrees C). The chromatographically purified, completely refolded three-disulfide species were not stable above the optimal refolding temperature in the presence of glutathione. The stability of each of them was determined from the far-UV CD thermal denaturation measurement at pH 3.9 in the absence of glutathione, where the denaturation was reversible. The transition temperature was lowest for delta 1 and highest for delta 4Ala. Precise values of difference in the transition temperature among the three-disulfide derivatives were found to correlate with those in the optimal refolding temperature. Next, the effect of glycerol, which has been shown to increase the refolding efficiency [Sawano et al. (1992) FEBS Lett. 303, 11-14], was examined for delta 1 in detail. The optimal temperature for refolding increased by 3-4 degrees C with the increase in glycerol concentration by 10%. The amount of increase in the optimal refolding temperature was nearly equal to the amount of the increase in thermal stability in the presence of glycerol of refolded and purified delta 1.(ABSTRACT TRUNCATED AT 250 WORDS)

[A case report of tetralogy of Fallot associated with total occlusion of the right coronary artery and complicated with infective endocarditis].

A 31-year-old male with tetralogy of Fallot (TF) and total occlusion of the right coronary orifice complicated with infective endocarditis successfully underwent total repair of TF and coronary artery bypass graft (CABG). The patient had severely suffered from symptoms including breathlessness, palpitation (SVT) and chest pain. The coronary arteriography revealed occlusion of the right coronary orifice. The preoperative course was further complicated by endocarditis with vegetation of the aortic valve that did not respond to antibiotics. Concomitant surgical procedures consisting of TF repair, CABG to the right coronary artery with saphenous vein graft and vegetectomy of the aortic valve were carried out. The postoperative course was uneventful though he underwent cholecystectomy for symptomatic gall stones after TF repair. The patient is now in NYHA class II.

Efficient in vitro folding of the three-disulfide derivatives of hen lysozyme in the presence of glycerol.

Four derivatives of hen lysozyme, each lacking one native disulfide bond of the four in authentic lysozyme, were produced in Escherichia coli by expressing synthetic mutant genes. In the reoxidation reaction of the reduced derivatives purified from inclusion bodies, the addition of glycerol significantly enhanced the efficiency of folding and 'correct' disulfide bond formation. This enabled simple chromatographical purification of refolded materials. Purified 3SS-derivatives all showed lytic activities and secondary structures comparable to authentic lysozyme, which directly showed that none of the four native disulfide bonds is a prerequisite for 'correct' in vitro folding.

Further study on polyamine compositions in Vibrionaceae.

It has previously been reported that norspermidine, one of the unusual polyamines, is present in Vibrio species. To expand this observation, the cellular polyamine compositions of additional species and strains in the family Vibrionaceae (Vibrio, Photobacterium, Listonella, and Shewanella) as well as Aeromonas species and Plesiomonas shigelloides, which have been proposed to be excluded from Vibrionacea, were determined by using gas-liquid chromatography. Some Vibrio species previously reported were reexamined under the same conditions, and their results are included in this report. Norspermidine was detected as a major triamine in 23 of 24 Vibrio species, all of 4 Listonella species, and 3 of 5 Photobacterium species. Vibrio costicola, Photobacterium fischeri, and Photobacterium phosphoreum contained no norspermidine. Listonella species were indistinguishable from Vibrio species in their polyamine profiles. However, Schewanella putrefaciens ATCC 8071, formerly allocated in the genus Alteromonas, contained no norspermidine, and its polyamine profile was similar to those of four Aeromonas species, in which putrescine was exclusively found. Plesiomonas shigelloides was very similar to Escherichia coli in that putrescine and spermidine were predominant polyamines. Our data indicate that the occurrence of norspermidine may be very helpful as a generic marker in identification and classification of Vibrio and Listonella species. A gas-liquid chromatographic method with a nitrogen-selective detector was presented for rapid and sensitive detection of cellular norspermidine.

Effects of various triamines on cell-free polypeptide synthesis of Escherichia coli and on growth of its polyamine auxotrophs.

The effects of various synthetic triamines having a general structure, H2N(CH2)xNH(CH2)yNH2, where x = 2-5 and y = 2-8 (abbreviated, x-y; with 3-4 being spermidine itself), on poly(U)-directed polypeptide synthesis of Escherichia coli and on growth of its polyamine-requiring mutants were examined in comparison with those of spermidine. Except for 2-2 and 2-3, all of the triamines stimulated more or less polypeptide synthesis at suboptimal Mg2+ concentrations, but the Mg2+ concentration required for the maximal stimulatory effect was different for each triamine. The degree of maximal stimulation caused by 3-3 (norspermidine), 4-4 (homospermidine), or 4-5 was nearly comparable with that by spermidine. The acetylspermidines were inactive, however, they inhibited the spermidine-stimulated polyphenylalanine synthesis. Many of the triamines examined reduced the ratio of leucine to phenylalanine incorporation into polypeptides during poly(U)-directed translation, and the degree of this effect did not necessarily correspond with that of the stimulatory effect. Moreover, 2-4, 2-5, 3-3 and 4-4 could stimulate the growth of a polyamine auxotroph of E. coli, MA 261, as effectively as did spermidine. However, 3-3 was the only triamine which could fully replaced spermidine in promoting growth of a mutant strain, KK 101, which is more dependent on polyamines than MA 261. Thus, these results demonstrated that some synthetic triamines were as active as spermidine in eliciting these effects, and also that there were some differences among these effects in the structural requirement for triamine.

Effect of norspermidine and its related triamines on the cell-free polyphenylalanine synthesizing system from Vibrio parahaemolyticus.

The effect of norspermidine and its structurally related triamines on the cell-free polyphenylalanine synthesizing system from Vibrio parahaemolyticus was examined in connection with the requirement of the system for monovalent cation. In the absence of norspermidine, the maximal incorporation of [14C]phenylalanine into hot trichloroacetic acid insoluble material was observed under ionic conditions of 12 mM Mg2+ and 50 mM NH4+. K+ could partially substitute for NH4+, but Na+ could not. The addition of norspermidine to the polyphenylalanine synthetic reaction mixture not only lowered the optimal Mg2+ concentration, but it also stimulated the polyphenylalanine synthesis up to 2-fold with no significant increase in misincorporation of [14C]leucine. Other triamines having one or two methylene chains more than norspermidine were also effective in eliciting these effects. Furthermore, Na+ could not support the polyphenylalanine synthesis even in the presence of norspermidine and, on the contrary, inhibited the polyphenylalanine synthesis induced by NH4+ regardless of whether norspermidine was present or not. These findings are discussed in comparison with the properties of other bacterial cell-free systems.

Formation of hydroxynorspermidine from exogenously added 1,3-diaminopropan-2-ol in Vibrio species.

When Vibrio parahaemolyticus AQ 3627 was grown in the presence of 1,3-diaminopropan-2-ol (OH-Dap), a new compound accumulated in the cells. This was identified as hydroxynorspermidine (OH-Nspd), N-(3-aminopropyl)-1,3-diaminopropan-2-ol, by gas chromatography-mass spectrometry and thin-layer chromatography. It was also synthesized enzymatically from OH-Dap by a cell-free preparation from this strain. All other Vibrio strains examined also showed the ability to synthesize this compound, but none of the non-vibrio organisms did, indicating that OH-Dap is an in vivo substrate for the enzyme responsible for biosynthesis of norspermidine characteristically present in vibrios. These results suggest that the ability to synthesize OH-Nspd from OH-Dap present in the growth medium may be useful as an additional identifying factor for the genus Vibrio.

Identification of N1-acetylnorspermidine in Vibrio parahaemolyticus and an enzyme activity responsible for its formation.

N1-Acetylnorspermidine [CH3CONH(CH2)3 NH(CH2)3NH3] was identified in Vibrio parahaemolyticus, which contains norspermidine as a major polyamine. This is the first example for the natural occurrence of monoacetylated unusual polyamine. The N1-acetylnorspermidine content was the highest 4 h after inoculation. Incubation of norspermidine and acetyl CoA with a cell extract from V. parahaemolyticus produced N1-acetylnorspermidine. A remarkable increase in specific activity of the acetyltransferase was observed at the exponential phase of growth. Spermidine also served as a substrate for the enzyme, with the formation of two isomers of the acetylspermidines (N1-acetylspermidine was predominant), but the reaction rate was less than 50% of that with norspermidine. These results suggest that norspermidine in V. parahaemolyticus may be associated with the cell growth and its role may be controlled through acetylation, as reported for spermidine in Escherichia coli.