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M Potts

Publications and source records attributed to M Potts.

At least 37 records · Page 2Linked to original sources
PubMed2000

The use of the 2-aminobenzoic acid tag for oligosaccharide gel electrophoresis.

Gel electrophoresis of fluorophore labeled saccharides provides a rapid and reliable method to screen enzymatic and/or chemical treatments of polysaccharides and glycoconjugates, as well as a sensitive and efficient microscale method to separate and purify oligosaccharides for further analysis. A simple and inexpensive method of derivatization and analysis using 2-aminobenzoic acid (anthranilic acid, AA) is described and applied to the extracellular polysaccharide released by the desiccation tolerant cyanobacterium Nostoc commune DRH-1. The results of these analyses suggest a possible protective functionality of two pendent groups, as well as a potential relationship between these groups and the desiccation tolerance of the organism.

Carbohydrate Sequence↗
PubMed2000

N-(cyclohexanecarboxyl)-O-phospho-l-serine, a minimal substrate for the dual-specificity protein phosphatase IphP.

Three dual-specific phosphatases [DSPs], IphP, VHR, and Cdc14, and three protein-tyrosine phosphatases [PTPs], PTP-1B, PTP-H1, and Tc-PTPa, were challenged with a set of low molecular weight phosphoesters to probe the factors underlying the distinct substrate specificities displayed by these two mechanistically homologous families of protein phosphatases. It was observed that beta-naphthyl phosphate represented an excellent general substrate for both PTPs and DSPs. While DSPs tended to hydrolyze alpha-naphthyl phosphate at rates comparable to that of the beta-isomer, the PTPs PTP-1B and Tc-PTPa did not. PTP-H1, however, displayed high alpha-naphthyl phosphatase activity. Intriguingly, PTP-H1 also displayed much higher protein-serine phosphatase activity in vitro, 0.2-0.3% that toward equivalent tyrosine phosphorylated proteins, than did PTP-1B or Tc-PTPa. The latter two PTPs discriminated between the serine- and tyrosine-phosphorylated forms of two test proteins by factors of >/=10(4)-10(6). While free phosphoserine represented an extremely poor substrate for all of the DSPs examined, the addition of a hydrophobic "handle" to form N-(cyclohexanecarboxyl)-O-phospho-l-serine produced a compound that was hydrolyzed by IphP with high efficiency, i.e., at a rate comparable to that of free phosphotyrosine or p-nitrophenyl phosphate. VHR also hydrolyzed N-(cyclohexanecarboxyl)-O-phospho-l-serine (1 mM) at a rate approximately one-tenth that of beta-naphthyl phosphate. None of the PTPs tested exhibited significant activity against this compound. However, N-(cyclohexanecarboxyl)-O-phospho-l-serine did not prove to be a universal substrate for DSPs as Cdc14 displayed little propensity to hydrolyze it.

Binding Sites↗
PubMed2000

Solution 1H NMR study of the heme cavity and folding topology of the abbreviated chain 118-residue globin from the cyanobacterium Nostoc commune.

The globin from the cyanobacterium Nostoc commune, abbreviated GlbN, which appears to serve as a part of a terminal oxidase rather than as a respiratory pigment, displays relatively normal O2 binding properties, despite the highly abbreviated polypeptide chain, (118 residues) relative to more conventional globins [Thorsteinsson, M. V. , Bevan, D. R., Potts, M., Dou, Y., Eich, R. F., Hargrove, M. S., Gibson, Q. H., and Olson, J. S. (1999) Biochemistry 38, 2117-2126]. The nature of the heme cavity and the general folding topology of this cyanoglobin were investigated by solution 1H NMR to establish the extent to which, and the manner in which, this compact globin adheres to the standard globin fold. This represents by far the smallest globin subjected to structural analysis. The paramagnetic cyanomet derivative was selected because its characteristically large magnetic anisotropy imparts significant dipolar shifts which both improve resolution to greatly facilitate assignments and serve as indicators of the folding topology of the globin. Identification of the axial His 70 and highly conserved Phe 35 (CD1) determined the absolute orientation of the heme and proximal His. Sequential assignments of four helical and one loop segments, which exhibit dipolar contacts to the heme and among each other, confirm the presence of well-conserved F, G, and H helices and the FG corner. The majority of the abbreviation of the chain relative to the more conventional length globins is accommodated in the A-D helices, of which the last is completely missing. The distal residue which provides a H-bond to bound ligand is identified as Gln 43, but the expected helical position E7 could not be confirmed. His 46, placed at position E10, is found to adopt alternate orientations into, and out of, the heme cavity depending on protonation state, suggesting the presence of a Bohr effect at low pH. It is shown that the dipolar shifts exhibited by backbone protons for the assigned residues conform well to those observed for other cyanomet globins and further support a conserved Mb fold. Perturbed medium-range dipolar contacts and the pH-independent backbone proton lability of the F helix are interpreted in terms of a holoprotein which is less stable than a conventional length globin.

Amino Acid Sequence↗
PubMed2000

Engineering desiccation tolerance in Escherichia coli.

Recombinant sucrose-6-phosphate synthase (SpsA) was synthesized in Escherichia coli BL21DE3 by using the spsA gene of the cyanobacterium Synechocystis sp. strain PCC 6803. Transformants exhibited a 10,000-fold increase in survival compared to wild-type cells following either freeze-drying, air drying, or desiccation over phosphorus pentoxide. The phase transition temperatures and vibration frequencies (P==O stretch) in phospholipids suggested that sucrose maintained membrane fluidity during cell dehydration.

Cyanobacteria↗
PubMed2000

Active Fe-containing superoxide dismutase and abundant sodF mRNA in Nostoc commune (Cyanobacteria) after years of desiccation.

Active Fe-superoxide dismutase (SodF) was the third most abundant soluble protein in cells of Nostoc commune CHEN/1986 after prolonged (13 years) storage in the desiccated state. Upon rehydration, Fe-containing superoxide disumutase (Fe-SOD) was released and the activity was distributed between rehydrating cells and the extracellular fluid. The 21-kDa Fe-SOD polypeptide was purified, the N terminus was sequenced, and the data were used to isolate sodF from the clonal isolate N. commune DRH1. sodF encodes an open reading frame of 200 codons and is expressed as a monocistronic transcript (of approximately 750 bases) from a region of the genome which includes genes involved in nucleic acid synthesis and repair, including dipyrimidine photolyase (phr) and cytidylate monophosphate kinase (panC). sodF mRNA was abundant and stable in cells after long-term desiccation. Upon rehydration of desiccated cells, there was a turnover of sodF mRNA within 15 min and then a rise in the mRNA pool to control levels (quantity of sodF mRNA in cells in late logarithmic phase of growth) over approximately 24 h. The extensive extracellular polysaccharide (glycan) of N. commune DRH1 generated superoxide radicals upon exposure to UV-A or -B irradiation, and these were scavenged by SOD. Despite demonstrated roles for the glycan in the desiccation tolerance of N. commune, it may in fact be a significant source of damaging free radicals in vivo. It is proposed that the high levels of SodF in N. commune, and release of the enzyme from dried cells upon rehydration, counter the effects of oxidative stress imposed by multiple cycles of desiccation and rehydration during UV-A or -B irradiation in situ.

Amino Acid Sequence↗
PubMed2000

Structural characterization of the released polysaccharide of desiccation-tolerant Nostoc commune DRH-1.

The structure of the viscous extracellular polysaccharide (glycan) of desiccation-tolerant Nostoc commune DRH-1 was determined through chromatographic and spectroscopic methods. The polysaccharide is novel in that it possesses a 1-4-linked xylogalactoglucan backbone with D-ribofuranose and 3-O-[(R)-1-carboxyethyl]-D-glucuronic acid (nosturonic acid) pendant groups. The presence of D-ribose and nosturonic acid as peripheral groups is unusual, and their potential roles in modulating the rheological properties of the glycan are discussed. Nosturonic acid was present in the glycans of N. commune from diverse geographic locations, suggesting that this uronic acid is an integral component of this cosmopolitan anhydrophile.

Carbohydrate Conformation↗
PubMed2000

Thinking about vaginal microbicide testing.

A vaginal microbicide could slow the spread of HIV. To date, volunteers in placebo-controlled trials of candidate microbicides have been counseled to use condoms. This does not reduce the number of volunteers exposed to possible risk, but it shifts the allotment of risk from those conducting the trial to those women who may be least able to make autonomous decisions. Alternative ways of meeting the obligation to offer volunteers active benefits are explored. Counseling the use of condoms prolongs clinical trials and could cause tens of thousands of otherwise avoidable deaths.

Administration, Intravaginal↗
PubMed1999

Life among the primitives: protein O-phosphatases in prokaryotes.

Prokaryotes contain at least five distinct families of protein O-phosphatases, including AceK, the chimeric isocitrate dehydrogenase kinase/phosphatase, and four protein phosphatase families first identified and characterized in Eukaryotes. The latter consist of the PPP and PPM families of protein-serine/threonine phosphatases, and the low molecular weight and conventional families of protein-tyrosine phosphatases. Prokaryotic protein O-phosphatases participate in the regulation of metabolic processes and the transduction of environmental signals. Certain pathogenic bacteria employ protein-tyrosine phosphatases as virulence factors, injecting them into host cells where they enzymatically perturb the phosphorylation state of proteins therein. While our understanding of protein O-phosphorylation events in Prokaryotes only now is emerging from its infancy, their phylogenetic diversity and malleability to genetic manipulation render these "simple'" organisms powerful vehicles for answering fundamental questions concerning the origins and evolution of this key biological regulatory mechanism.

Phosphoprotein Phosphatases↗
PubMed1999

A cyanobacterial hemoglobin with unusual ligand binding kinetics and stability properties.

The glbN gene of the cyanobacterium Nostoc commune UTEX 584 encodes a hemoprotein, named cyanoglobin, that has high oxygen affinity. The basis for the high oxygen affinity of cyanoglobin was investigated through kinetic studies that utilized stopped-flow spectrophotometry and flash photolysis. Association and dissociation rate constants were measured at 20 degrees C for oxygen, carbon monoxide, nitric oxide, and methyl and ethyl isocyanides. The association rate constants for the binding of these five ligands to cyanoglobin are the highest reported for any naturally occurring hemoglobin, suggesting an unhindered and apolar ligand binding pocket. Cyanoglobin also shows high rates of autoxidation and hemin loss, indicating that the prosthetic group is readily accessible to solvent. The ligand binding behavior of cyanoglobin was more similar to that of leghemoglobin a than to that of sperm whale myoglobin. Collectively, the data support the model of cyanoglobin function described by Hill et al. [(1996) J. Bacteriol. 178, 6587-6598], in which cyanoglobin sequesters oxygen, and presents it to, or is a part of, a terminal cytochrome oxidase complex in Nostoc commune UTEX 584 under microaerobic conditions, when nitrogen fixation, and thus ATP demand, is maximal.

Bacterial Proteins↗
PubMed1999

Making Cairo work.

The 1994 International Conference on Population and Development set broad new goals for family planning and reproductive health. The resources available to fund these much needed programmes, however, are much smaller than was originally calculated. To divide the limited budgets for the maximum health impact, likely resource flows need to be set against the cost of various family planning and reproductive health interventions. Preliminary analysis suggests that selection of cost-effective delivery of family planning services would still meet much of the need for family planning, and that some progress could be made towards improved control of sexually transmitted diseases.

Congresses as Topic↗
PubMed1999

International aspects of ethical problems in obstetrics and gynaecology.

Until the middle of the twentieth century, family planning was commonly condemned as an immoral enterprise. This chapter argues that ethical disapproval made access to fertility regulation difficult, and that while the rich and educated were often able to access the services they needed, typically the poor could not. Thus, ethical interpretations caused much of the differential fertility observed between social classes, ethnic groups and ultimately much of the explosion in population that has characterized the last 50 years. Since the 1960s human rights have been interpreted to encompass the right to decide the number and spacing of children and as a result access to contraception has improved. Where several methods of contraception (backed up by safe abortion) are available, fertility always falls. But, unfortunately, consensus has not been reached on how to specify particular sets of rights (e.g. decision-making for adolescents), and no consensus exists on how to balance the opposing rights of the mother and fetus in the case of abortion. The ethics of the one-child family in China is also noted.

Abortion, Legal↗
PubMed1998

The serine, threonine, and/or tyrosine-specific protein kinases and protein phosphatases of prokaryotic organisms: a family portrait.

Inspection of the genomes for the bacteria Bacillus subtilis 168, Borrelia burgdorferi B31, Escherichia coli K-12, Haemophilus influenzae KW20, Helicobacter pylori 26695, Mycoplasma genitalium G-37, and Synechocystis sp PCC 6803 and for the archaeons Archaeoglobus fulgidus VC-16 DSM4304, Methanobacterium thermoautotrophicum delta H, and Methanococcus jannaschii DSM2661 revealed that each contains at least one ORF whose predicted product displays sequence features characteristic of eukaryote-like protein-serine/threonine/tyrosine kinases and protein-serine/threonine/tyrosine phosphatases. Orthologs for all four major protein phosphatase families (PPP, PPM, conventional PTP, and low molecular weight PTP) were present in the bacteria surveyed, but not all strains contained all types. The three archaeons surveyed lacked recognizable homologs of the PPM family of eukaryotic protein-serine/threonine phosphatases; and only two prokaryotes were found to contain ORFs for potential phosphatases from all four major families. Intriguingly, our searches revealed a potential ancestral link between the catalytic subunits of microbial arsenate reductases and the protein-tyrosine phosphatases; they share similar ligands (arsenate versus phosphate) and features of their catalytic mechanism (formation of arseno-versus phospho-cysteinyl intermediates). It appears that all prokaryotic organisms, at one time, contained the genetic information necessary to construct protein phosphorylation-dephosphorylation networks that target serine, threonine, and/or tyrosine residues on proteins. However, the potential for functional redundancy among the four protein phosphatase families has led many prokaryotic organisms to discard one, two, or three of the four.

Amino Acid Sequence↗