Differential abundance of sarcoplasmic proteome explains animal effect on beef Longissimus lumborum color stability.

The sarcoplasmic proteome of beef Longissimus lumborum demonstrating animal-to-animal variation in color stability was examined to correlate proteome profile with color. Longissimus lumborum (36 h post-mortem) muscles were obtained from 73 beef carcasses, aged for 13 days, and fabricated to 2.5-cm steaks. One steak was allotted to retail display, and another was immediately vacuum packaged and frozen at -80°C. Aerobically packaged steaks were stored under display, and color was evaluated on days 0 and 11. The steaks were ranked based on redness and color stability on day 11, and ten color-stable and ten color-labile carcasses were identified. Sarcoplasmic proteome of frozen steaks from the selected carcasses was analyzed. Nine proteins were differentially abundant in color-stable and color-labile steaks. Three glycolytic enzymes (phosphoglucomutase-1, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase M2) were over-abundant in color-stable steaks and positively correlated (P<0.05) to redness and color stability. These results indicated that animal variations in proteome contribute to differences in beef color.

A highly active phosphoglucomutase from Clostridium thermocellum: cloning, purification, characterization and enhanced thermostability.

AIMS: Discovery and utilization of highly active and thermostable phosphoglucomutase (PGM) would be vital for biocatalysis mediated by multiple enzymes, for example, high-yield production of enzymatic hydrogen. METHODS AND RESULTS: The thermophilic cellulolytic bacterium Clostridium thermocellum was hypothesized to have a very active PGM because of its key role in microbial cellulose utilization. The Cl. thermocellum ORF Cthe1265 encoding a putative PGM was cloned and expressed in Escherichia coli. The purified enzyme appeared to be a monomer with an estimated molecular weight of 64.9 kDa. This enzyme was found to be a dual-specificity enzyme - PGM/phosphomannomutase (PMM). Mg(2+) and Mn(2+) were activators. Ser144 was identified as an essential catalytic residue through site-directed mutagenesis. The k(cat) and K(m) of PGM were 190 s(-1) and 0.41 mmol l(-1) on glucose-1-phosphate and 59 s(-1) and 0.44 mmol l(-1) on mannose-1-phosphate, respectively, at 60 degrees C. Thermostability of PGM at a low concentration (2 nmol l(-1), 100 U l(-1)) was enhanced by 12-fold (i.e. t(1/2) = 72 h) at 60 degrees C with addition of bovine serum albumin, Triton X-100, Mg(2+)and Mn(2+). CONCLUSIONS: The ORF Cthe1265 was confirmed to encode a PGM with PMM activity. This enzyme was the most active PGM reported. SIGNIFICANCE AND IMPACT OF THE STUDY: This highly active PGM with enhanced thermostability would be an important building block for in vitro synthetic biology projects (complicated biotransformation mediated by multiple enzymes in one pot).

Random mutagenesis of the PM promoter as a powerful strategy for improvement of recombinant-gene expression.

The inducible Pm-xylS promoter system has proven useful for production of recombinant proteins in several gram-negative species and in high-cell-density cultivations of Escherichia coli. In this study we subjected a 24-bp region of Pm (including the -10 element) to random mutagenesis, leading to large mutant libraries in E. coli. Low-frequency-occurring Pm mutants displaying strongly increased promoter activity (up-mutants) could be efficiently identified by using beta-lactamase as a reporter. The up-mutants typically carried multiple point mutations positioned throughout the mutagenized region, combined with deletions around the transcription start site. Mutants displaying up to about a 14-fold increase in beta-lactamase expression (relative to wild-type Pm) were identified without loss of the inducible phenotype. The mutants also strongly stimulated the expression of two other reporter genes, luc (encoding firefly luciferase) and celB (encoding phosphoglucomutase), and were found to significantly improve (twofold) a previously optimized process for high-level recombinant production of the medically important granulocyte-macrophage colony-stimulating factor in E. coli under high-cell-density conditions. These results demonstrate the potential of using random mutagenesis of promoters to improve protein expression at industrial levels and indicate that targeted modifications of individual functional elements are not sufficient to obtain optimized promoter sequences.

Genetic responses to metal contamination in two clams: Ruditapes decussatus and Ruditapes philippinarum.

Coastal ecosystems are subjected to a wide variety of disturbances, including those due to xenobiotics of agricultural and industrial origin. These pollutants as heavy metals can modify the genetic diversity of populations by favouring or counter-selecting certain alleles or genotypes by differential mortality. In the present study, two genetic markers (phosphoglucomutase and glucosephosphate isomerase) and a protein marker (metallothionein) were monitored in order to determine the impact of heavy metals in different clam populations. Analysis of the genetic structure of the clam populations examined reveals that those inhabiting environments contaminated by heavy metals exhibit a higher allelic diversity and possess alleles at PGM loci that could be selected by the presence of heavy metals. The evaluation of metallothionein levels using a specific polyclonal antibody developed in the Pacific oyster (Crassostrea gigas) demonstrated the existence of a relationship between metallothionein concentrations and the level of metal pollution for clam populations sampled from different sites. An inter-specific difference was also detected between Ruditapes decussatus and Ruditapes philippinarum living in sympatry at the same site, suggesting a differential response of these two species upon exposure to an identical heavy metal concentration.

A parafusin-related Toxoplasma protein in Ca2+-regulated secretory organelles.

We cloned a gene, PRPI, of Toxoplasma gondii encoding a 637-amino-acids protein having a calculated mass of 70 kDa. The sequence showed high homology to parafusin, a protein that in Paramecium tetraurelia participates in Ca2+-regulated exocytosis and is a paralog of phosphoglucomutase. We show that Toxoplasma gondii homogenate and an expressed recombinant PRP1 fusion protein cross-react with a specific peptide-derived antibody to parafusin in Western blots. Antibodies to the recombinant PRP1 showed cross-reaction with parafusin and recognized PRP1, as bands at M, 63 x 10(3) and 68 x 10(3), respectively. PRP1 is labeled when Toxoplasma gondii cells are incubated with inorganic 32P and appears as the major band on autoradiograms of SDS-PAGE gels. The localization of PRP1 was examined in secretory organelles of Toxoplasma gondii by deconvolution light microscopy followed by three dimensional reconstruction using pairwise combinations of specific antibodies. PRP1 localized to the apical third of the cell. It co-localized with micronemes, the only secretory organelle the secretion of which is Ca2+ dependent. Quantification of the co-localized stain suggests that only mature micronemes ready for exocytosis have PRP1. These findings suggest that PRP1, parafusin and other members of the phosphoglucomutase superfamily have a conserved role in Ca2+-regulated exocytic processes.

Maltose metabolism of Lactobacillus sanfranciscensis: cloning and heterologous expression of the key enzymes, maltose phosphorylase and phosphoglucomutase.

The maltose degradation operon containing genes encoding maltose phosphorylase mapA and phosphoglucomutase pgmA from Lactobacillus sanfranciscensis DSM20451T were cloned and expressed in Escherichia coli. These genes represent the first genetic data available for this species beyond taxonomic classification. MapA encodes a 754-amino acid polypeptide representing maltose phosphorylase, MapA, with a calculated molecular mass of 85.7 kDa. Comparative sequence analysis showed that mapA is of a new type distinct from other alpha-glucosidase genes sequenced so far. Putatively, pyridoxal 5'-phosphate is required as cofactor. The deduced amino acid sequence of pgmA shows an overall similarity of 39% to the phosphoglucomutase of Lactococcus lactis. pgmA is separated by a single nucleotide from the preceding mapA gene indicating effective translation by translational coupling. Upon subcloning mapA was heterologously expressed in E. coli. Additionally, upstream of the maltose-degrading operon ORF1 and ORF2 are located in the opposite direction. These genes show homology to fabZ and accB from E. coli and Bacillus subtilis, respectively, both involved in fatty acids biosynthesis.

An experimental study on carbon flow in Escherichia coli as a function of kinetic properties and expression levels of the enzyme phosphoglucomutase.

Mutants of Escherichia coli deficient in phosphoglucomutase accumulate amylose when the cells are grown on maltose or galactose as carbon source. In the presence of physiological levels of phosphoglucomutase, most of the sugar is catabolized, leading to strongly reduced levels of amylose accumulation. By varying the expression level of heterologous phosphoglucomutase, we show that the minimum level needed to block amylose accumulation corresponds to a phosphoglucomutase activity of 150-600 nmole substrate transformed per min per mg of total soluble protein. Mutant phosphoglucomutases with strongly reduced Vmax values and increased Km values for the substrate glucose-1-phosphate or the co-substrate glucose-1,6-diphosphate, could also reduce amylose accumulation, but much higher enzyme expression levels were required.

The femR315 gene from Staphylococcus aureus, the interruption of which results in reduced methicillin resistance, encodes a phosphoglucosamine mutase.

The femR315 gene was recently identified by Tn551 insertional mutagenesis as one of the new auxiliary genes, the alteration of which resulted in a drastically reduced methicillin resistance of the Staphylococcus aureus strain COL. femR315 (also known as femD) theoretically encoded a protein of 451 amino acids showing significant amino acid sequence homology with phosphoglucomutases and similar enzymes catalyzing the isomerization of hexoses and hexosamine phosphates (S. Wu, H. de Lencastre, A. Sali, and A. Tomasz, Microb. Drug Resist. 2:277-286, 1996). We describe here the overproduction and purification of the FemR315 protein as well as its identification as the phosphoglucosamine mutase which catalyzes the formation of glucosamine-1-phosphate from glucosamine-6-phosphate, the first step in the reaction sequence leading to the essential peptidoglycan precursor UDP-N-acetylglucosamine. On the basis of these findings, we propose to change the names femR315 and femD to the functionally more appropriate name glmM.

Construction and use of a versatile set of broad-host-range cloning and expression vectors based on the RK2 replicon.

The plasmid vectors described in this report are derived from the broad-host-range RK2 replicon and can be maintained in many gram-negative bacterial species. The complete nucleotide sequences of all of the cloning and expression vectors are known. Important characteristics of the cloning vectors are as follows: a size range of 4.8 to 7.1 kb, unique cloning sites, different antibiotic resistance markers for selection of plasmid-containing cells, oriT-mediated conjugative plasmid transfer, plasmid stabilization functions, and a means for a simple method for modification of plasmid copy number. Expression vectors were constructed by insertion of the inducible Pu or Pm promoter together with its regulatory gene xylR or xylS, respectively, from the TOL plasmid of Pseudomonas putida. One of these vectors was used in an analysis of the correlation between phosphoglucomutase activity and amylose accumulation in Escherichia coli. The experiments showed that amylose synthesis was only marginally affected by the level of basal expression from the Pm promoter of the Acetobacter xylinum phosphoglucomutase gene (celB). In contrast, amylose accumulation was strongly reduced when transcription from Pm was induced. CelB was also expressed with a very high induction ratio in Xanthomonas campestris. These experiments showed that the A. xylinum celB gene could not complement the role of the bifunctional X. campestris phosphoglucomutase-phosphomannomutase gene in xanthan biosynthesis. We believe that the vectors described here are useful for cloning experiments, gene expression, and physiological studies with a wide range of bacteria and presumably also for analysis of gene transfer in the environment.

Improved broad-host-range RK2 vectors useful for high and low regulated gene expression levels in gram-negative bacteria.

This report describes the construction and use of improved broad-host-range expression vectors based on the previously constructed pJB137 and pJB653 plasmids (Blatny et al., 1997). These vectors contain the minimal replicon of RK2 and the inducible Pu or Pm promoters together with their regulatory xylR or xylS genes, respectively, from the Pseudomonas putida TOL plasmid pWWO. A set of ATG vectors were derived from pJB653, and these vectors are characterized by the relatively small size, the presence of multiple cloning sites downstream of Pm, the establishment of their nucleotide sequence, the presence of RK2 oriT, and different antibiotic selection markers. The copy numbers of all the vectors can easily be modified by using copy-up mutations of the trfA gene, required for initiation of replication of RK2 replicons. The vectors were used to study the expression levels of the Acetobacter xylinum phosphoglucomutase gene celB and the two commonly used reporter genes luc and cat in Escherichia coli, Pseudomonas aeruginosa, and Xanthomonas campestris. Good induction properties and tight regulation of Pm were achieved in all three species tested, and higher gene expression levels were obtained by using the ATG vectors compared to pJB653. By introducing different trfA copy-up mutations into the vectors, a wide range of gene expression levels from Pu and Pm were obtained in E. coli. Induced expression levels of luc, cat, and celB from Pm were found to be comparable to or higher than those from the Ptrc and PT7 promoters located on high copy number plasmids. The induced levels of Luc activity were higher in P. aeruginosa than in E. coli, indicating that these vectors may be useful for maximization of gene expression in strains other than E. coli. We believe that the well-characterized vectors described here are useful for gene expression studies and routine cloning experiments in many Gram-negative bacteria.

Effect of trehalose during stress in a heat-shock resistant mutant of Saccharomyces cerevisiae.

Cells of a heat-shock resistant mutant were approximately 1000-times more resistant to lethal heat shock than those of the parental strain. We observed that exponentially growing cells of the mutant synthesized trehalose and showed increased osmotolerance, dehydration tolerance an ethanol tolerance, a fact not observed in wild type strains. The mutant synthesizes constitutively six proteins, among them two proteins of 56 and 63 kDa. Interestingly these molecular weights could correspond to the subunit of trehalose-6-phosphate synthase and to phosphoglucomutase II, respectively. Our results showed that glucose-growing cells of the hsr 1 mutant possessed high levels of activity of these enzymes when compared to the control strain.

Lipooligosaccharide biosynthesis in pathogenic Neisseria. Cloning, identification, and characterization of the phosphoglucomutase gene.

The lipooligosaccharide (LOS) of pathogenic Neisseria is an important factor in disease pathogenesis. Little is known about the genes involved in neisserial LOS biosynthesis. To elucidate specific LOS biosynthetic genes, we screened a Tn916 library that was constructed in Neisseria meningitidis strain NMB. This strain expresses a single LOS that has an molecular mass of 4.5 kDa and binds monoclonal antibody (mAb) 3F11. This library was screened using a mAb panel that recognizes structural differences in neisserial LOS oligosaccharides. A stable LOS mutant of strain NMB was identified which we designated NMB-R6. This mutant expressed an LOS with an molecular mass of approximately 3.1-3.2 kDa and did not bind mAb 3F11. Genomic DNA from this mutant transformed N. meningitidis strain NMB to the tetracycline resistant NMB-R6 phenotype greater than 10(-4)/recipient/micrograms of DNA. In addition, we transformed Neisseria gonorrhoeae strain 1291 (LOS phenotype molecular mass 4.5 kDa, mAb 3F11+) to the NMB-R6 LOS phenotype with N. meningitidis NMB-R6 genomic DNA. Analysis of N. gonorrhoeae strain 1291-R6 LOS by mass spectroscopy showed that the LOS oligosaccharide structure is GlcNAc-->Hep2phosphoethanolamine-->2-keto-3-deoxymannooctuloson ic acid (where Hep is heptose). Sequence analysis showed that the transposon is inserted into the 3' end of a gene that has homology to the human phosphoglucomutase (PGM) gene. Sequence comparison indicated that the putative PGM gene in N. gonorrhoeae 1291 and N. meningitidis NMB had 92% identity at the DNA level. PGM and glucokinase activity was present in cell free extracts of N. meningitidis NMB and N. gonorrhoeae strain 1291. N. meningitidis NMB-R6 and N. gonorrhoeae strain 1291-R6 had no detectable PGM activity, whereas glucokinase activity was similar to the wild type strains. PGM activity can be reconstituted in N. meningitidis strain NMB-R6 by transformation with the cloned PGM gene. SDS-polyacrylamide gel electrophoresis demonstrated that NMB-R6 transformed with the PGM gene expressed the 3F11+, 4.5-kDa LOS of the parent NMB strain. The inability of N. meningitidis NMB-R6 and N. gonorrhoeae strain 1291-R6 to convert glucose 6-phosphate to glucose 1-phosphate results in the truncated LOS phenotype expressed by these mutants.

Isolation and expression of a rat liver cDNA encoding phosphoglucomutase.

A cDNA encoding phosphoglucomutase (PGM) has been isolated from a rat liver cDNA library following screening with a polymerase chain reaction product. The cDNA was found to contain a 53-base-pair (bp) 5' untranslated region (5' UTR), a single start codon and consensus initiation sequence, an open reading frame (ORF) of 1686 bp, and a 3' untranslated tail. A comparison to the rabbit and human muscle PGM cDNAs [Whitehouse et al., Proc. Natl. Acad. Sci. USA 89 (1992) 411-415] showed 90% identity of rat cDNA to both, while a comparison to the deduced amino acid sequences showed 97 and 96% identity, respectively. Northern blot analyses determined that PGM was encoded by a single mRNA in rat liver, of approximately 2.2 kb. Following transfection of COS-7 cells with a plasmid containing the entire PGM ORF, indirect immunofluorescence analyses using a PGM-specific monoclonal antibody determined that approximately 5% of the cells displayed 50-100 times greater fluorescence than that seen in the remainder of the cells or in mock transfects. The enhanced production of PGM was also demonstrated by Western blotting and by enzymatic activity assays.

Transcription of a yeast phosphoglucomutase isozyme gene is galactose inducible and glucose repressible.

The Saccharomyces cerevisiae GAL5 (PGM2) gene was isolated and shown to encode the major isozyme of phosphoglucomutase. Northern (RNA) blot hybridization revealed that the GAL5 transcript level increased three- to fourfold in response to galactose and was severely repressed in response to glucose. Total cellular phosphoglucomutase activity was likewise responsive to galactose and to glucose, and this responsiveness was found to be due primarily to variation in the activity of the major isozyme of phosphoglucomutase. These results imply that the major and minor isozymes of phosphoglucomutase have distinct roles in yeast cells. The galactose inducibility of GAL5 was found to be under the control of the GAL4, GAL80, and GAL3 genes. In striking contrast to other galactose-inducible genes, the GAL5 gene exhibited an unusually high GAL4-independent basal level of expression. These results have implications for metabolic trafficking.

Adaptive significance of differences in the tissue-specific expression of a phosphoglucomutase gene in rainbow trout.

We have investigated the phenotypic effects of a mutant allele that results in the expression of a phosphoglucomutase locus (Pgm1) in the liver of rainbow trout. Embryos with liver Pgm1 expression hatch earlier than embryos without liver Pgm1 expression. These differences apparently result from increased flux through glycolysis in embryos with liver PGM1 activity while they are dependent on the yolk for energy. Fish with liver PGM1 activity are also more developmentally buffered, as indicated by less fluctuating asymmetry of five bilateral meristic traits. The more rapidly developing individuals begin exogenous feeding earlier and achieve a size advantage that is maintained until sexual maturity. This size advantage produces a significant tendency for earlier age of sexual maturity. These results show that different genotypes at this regulatory gene result in important phenotypic differences that are likely to be of important adaptive significance.

Chinese hamster X mouse hybrid cells segregating mouse chromosomes and isozymes.

Hybrid cells are readily formed by fusing clonal Chinese hamster cells to fresh, noncultured, adult mouse spleen cells followed by isolation in selective medium. The vast majority of such hybrids retain Chinese hamster chromosomes and isozymes while segregating mouse chromosomes and isozymes. The growth, plating efficiency, ease of karyology, and rapid segregation of mouse markers allows linkage tests in primary clones. Analysis of 13 isozymes showed 12 to be asyntenic and on epair (PGD-PGM2) to be syntenic This system will allow extensive somatic cell hybrid gene mapping in the mouse and permit a comparison of human and mouse linkage relationships.

Sexual differentiation in Aspergillus nidulans: the requirement for manganese and the correlation between phosphoglucomutase and the synthesis of reserve material.

Aspergillus nidulans was completely devoid of fruit bodies when grown on manganese deficient cultures. This result was shown earlier to be due to a lack of alpha-1,3 glucan in the cell wall. Several enzymes of carbon and nitrogen metabolism were investigated in an attempt to explain the absence of this reserve material. Synthesis of glucose-6-phosphate dehydrogenase, phosphoglucoisomerase and aldolase, were not strongly affected by manganese deficiency. However, phosphoglucomutase showed only 60% of the activity of the control cultures and it was argued that this was connected with the low amounts of alpha-1,3 glucan synthesized. Malate dehydrogenase was the enzyme the least affected by manganese deficiency and the two to threefold higher activity measured after glucose depletion might indicate the induction of the glyoxylate cycle. An impaired glutamine synthetase could explain the increase in activity observed for NAD-glutamine dehydrogenase.