Control of cell type in yeast by the mating type locus: The α1-α2 hypothesis

We have extended the genetic analysis of four mutants carrying defective MATα alleles in order to determine how the mating type locus controls yeast cell types: a, a, and $\text{a}\text{α}$. First, we have mapped the defect in the mutant VC73 to the mating type locus by diploid and tetraploid segregation analysis. Second, we have determined that the mutations in these strains define two complementation groups, MATα1 and MATα2. The MATα1 gene is proposed to be a positive regulator of α mating functions. The MATα2 gene product is proposed to have two roles, as a negative regulator of a-specific mating functions and as a regulator of $\text{a}\text{α}$ cell functions (required for sporulation, for inhibition of mating and other processes). This view of MATα leads to the prediction that matα1^?matα2^? mutants should have the mating ability of an a cell and that matα1^?matα2^?/MATα strains should mate as α and be unable to sporulate. Such double mutants have been constructed and behave as predicted. We therefore propose that a-specific mating functions in MATa cells are constitutively expressed due to the absence of the MATα2 gene product and that α-specific mating functions are not expressed due to the absence of the MATα1 gene product.     

Nonsex Genes in the Mating Type Locus of Candida albicans Play Roles in a/α Biofilm Formation,Including Impermeability and Fluconazole Resistance

The mating type locus (MTL) of Candida albicans contains the mating type genes and has, therefore, been assumed to play an exclusive role in the mating process. In mating-incompetent a/α cells, two of the mating type genes, MTLa1 and MTLα2, encode components of the a1-α2 corepressor that suppresses mating and switching. But the MTL locus of C. albicans also contains three apparently unrelated “nonsex” genes (NSGs), PIK, PAP and OBP, the first two essential for growth. Since it had been previously demonstrated that deleting either the a/α copy of the entire MTL locus, or either MTLa1 or MTLα2, affected virulence, we hypothesized that the NSGs in the MTL locus may also play a role in pathogenesis. Here by mutational analysis, it is demonstrated that both the mating type and nonsex genes in the MTL locus play roles in a/α biofilm formation, and that OBP is essential for impermeability and fluconazole resistance.     

Substitution of glycine-661 by serine in the α1(I) and α2(1) chains of type I collagen results in different clinical and biochemical phenotypes

We have characterised a point mutation causing the substitution of serine for glycine at position 661 of the 1(I) chain of type I collagen in a child with a severe form of osteogenesis imperfecta. An identical glycine substitution in the 2(I) chain was previously detected in a woman with post-menopausal osteoporosis. Two of her sons were heterozygous for the mutation and the third son was homozygous as a result of uniparental isodisomy. Biochemical profiles of the type I collagen heterotrimers were studied in each of the patients and compared with a control. Medium and cell-layer collagens were overmodified in all patients. Overmodification was obvious in the patient with the 1(I) mutation but mild in the patients with the 2(I) mutation, being slightly less evident in the heterozygote than in the homozygote. Investigation of the melting curves of the mutant collagen trimers in all three patients showed the same slight decrease in thermal stability and, hence, a lack of correlation with phenotypic severity. In contrast, the degree of overmodification of the collagen alpha chains was correlated with the phenotypic severity. The clinical observations in these patients illustrate the possibly predominant role of mutations in the collagen 1(I) chains over the same mutations in the 2(I) chains in determining the clinical outcome.     

Peroxisome proliferator-activated receptorα (PPARα) agonists down-regulate α2-macroglobulin expression by a PPARα-dependent mechanism

Fibrates are peroxisome proliferator-activated receptor alpha (PPARα) ligands used to normalize lipid and glucose parameters and exert anti-inflammatory effects. The acute-phase response (APR) is an important inflammatory process. One of the most important acute-phase proteins in rats is α2-macroglobulin (A2Mg). Whereas normal adult rats present low serum levels, pregnant rats display high amounts. Therefore, we used pregnant rats to detect the effect of fenofibrate on hepatic A2Mg expression by RT-PCR and Northern blot. Virgin rats were used as controls. The expression of other APR genes, a known fibrate-responder gene, gamma-chain fibrinogen (γ-Fib), and one gene from the same family as A2Mg, complement component 3 (C3), were also measured in liver. In order to determine whether the fibrate-effects were mediated by PPARα, wild-type mice and PPARα-null mice were also used and treated with WY-14,643 (WY) or di-2-ethylhexyl phthalate (DEHP). Fenofibrate depressed A2Mg expression in virgin rats, but expression was decreased more sharply in pregnant rats. Expression of C3 and γ-Fib was diminished after treatment only in pregnant rats. On the other hand, WY, but not DEHP, reduced A2Mg and γ-Fib expression in the livers of wild-type mice, without any effect in PPARα-null mice. WY or DEHP did not affect C3 expression. Therefore, A2Mg expression is modified by PPARα agonists not only in pregnant rats under augmented APR protein synthesis, but also in virgin rats and mice under basal conditions. Interestingly, our results also identify A2Mg as a novel PPARα agonist-regulated gene.     

Regioselectivity of substrate hydroxylation versus halogenation by a nonheme iron(IV)–oxo complex: possibility of rearrangement pathways

Several nonheme iron enzymes and biomimetic model complexes catalyze a substrate halogenation reaction. Recent computational studies (Borowski et al. J Am Chem Soc 132:12887-12898, 2010) on α-ketoglutarate dependent halogenase proposed an initial isomerization reaction that is important to give halogenated products. We present here a series of density functional theory calculations on a biomimetic model complex-[Fe(IV)(O)(TPA)Cl](+), where TPA is tris(2-pyridylmethyl)amine-and investigate the mechanisms of substrate halogenation versus hydroxylation using the reactant and its isomer where the oxo and chloro groups have changed positions. We show here that the reactions occur on a dominant quintet spin state surface, although the reactants are in a triplet state. Despite the fact that the reactants can exist in two stable isomers with the oxo group either trans or cis to the axial ligand, they react differently with substrates, where one gives dominant hydroxylation and the other gives dominant chlorination of substrates. The ligand in the cis position of the oxo group is found to be active in the reaction mechanism and donated to the substrate during the reaction. A detailed thermochemical analysis of possible reaction mechanisms reveals that the strengths of the Fe-OH and Fe-Cl bonds in the radical intermediates are the key reasons for this regioselectivity switch of hydroxylation over halogenation. This study highlights the differences between enzymatic and biomimetic halogenases, where the former only react after an essential isomerization step, which is not necessary in model complexes.     

Hydrolysis of glycopyranosyl phosphates of the β-d (or α-l) configuration by a plant phosphatase

An acid phosphatase hydrolyzing β-d-galactose 1-phosphate has been purified 12-fold from Phaseolus aureus seedlings. It is not affected by Mg⁺⁺ but is inhibited by fluoride, molybdate, inorganic phosphate, and some heavy-metal ions.A number of other glycopyranosyl phosphates of the β-d (or α-l) configuration were also effective substrates, while the α-d (or β-l) anomers were hydrolyzed at one-twentieth to one-thirtieth the rate. Non-glycosyl phosphates were hydrolyzed at a rate intermediate between that of the α and that of the β anomer, probably as a result of contamination by nonspecific phosphomonoesterase.     

Molecular recognition of Candida albicans (1->2)-β-mannan oligosaccharides by a protective monoclonal antibody reveals the immunodominance of internal saccharide residues

A self-consistent model of β-mannan oligosaccharides bound to a monoclonal antibody, C3.1, that protects mice against Candida albicans has been developed through chemical mapping, NMR spectroscopic, and computational studies. This antibody optimally binds di- and trisaccharide epitopes, whereas larger oligomers bind with affinities that markedly decrease with increasing chain length. The (1→2)-β-linked di-, tri-, and tetramannosides bind in helical conformations similar to the solution global minimum. Antibody recognition of the di- and trisaccharide is primarily dependent on the mannose unit at the reducing end, with the hydrophobic face of this sugar being tightly bound. Recognition of a tetrasaccharide involves a frameshift in the ligand interaction, shown by strong binding of the sugar adjacent to the reducing end. We show that frameshifting may also be deliberately induced by chemical modifications. Molecular recognition patterns similar to that of mAb C3.1, determined by saturation transfer difference-NMR, were also observed in polyclonal sera from rabbits immunized with a trisaccharide glycoconjugate. The latter observation points to the importance of internal residues as immunodominant epitopes in (1→2)-β-mannans and to the viability of a glycoconjugate vaccine composed of a minimal length oligosaccharide hapten.     

Induced parturition in dairy cattle: A comparison of a corticoid (flumethasone) and a prostaglandin (PGF2α) in different age groups

Parturitions were induced in 66 dairy cows and heifers of the German Black Pied breed, 11 to 13 days before term, using either a highly potent corticosteroid (flumethasone: 2 × 5 mg, 10 to 14 hr apart), or prostaglandin F_2α (20 mg i.v.) and initiating treatments either in the morning (A.M.) or late afternoon (P.M.). At those dose levels parturition was induced in $\text{50}\text{50}$ animals treated with flumethasone, and in $\text{9}\text{9}$ heifers, but only in $\text{5}\text{7}$ cows treated with PGF_2α; placentas were retained in all cases in which parturition was induced. Intervals between initiation of treatments and parturition were shorter in flumethasone-treated animals (flumethasone: 42.5 hr; PGF_2α 57.2 hr); with both drugs, they were approximately 10 to 15 hr shorter in younger animals. The first flumethasone treatment at P.M. prolonged the intervals to parturition in cows (first treatment A.M.: 37.8 hr; P.M.: 52.9 hr), but not in normal age heifers (A.M.: 27.6 hr; P.M.: 25.9 hr); in early bred heifers, this trend was reversed (A.M. 41.6 hr; P.M.: 31.8 hr). No circadian differences in response to PGF were noted. Mean intervals to postpartum conceptions were 93 and 94 days for PGF_2α-treated cows and heifers, and 123.5 and 125 days for flumethasone-treated cows and heifers, respectively.     

Site specific inhibition by α-benzyl-α-bromomalodinitrile (BBMD) of electron transport in spinach chloroplasts

The addition of α-benzyl-α-bromomalodinitrile to different controlled states (non-phosphorylating [2]. phosphorylating [3], ATP-inhibited [4] and uncoupled) of photosynthetic electron transport to ferricyanide or benzoquinone demonstrate a significant inhibition in isolated spinach chloroplasts. α-Benzyl-α-bromomalodinitrile pretreatement of isolated chloroplasts or addition of α-benzyl-α-bromomalodinitrile at the onset of illumination completely abolished the O₂ evolving reaction. The level of the steady state fluorescence in intact chloroplasts showed a α-benzyl-α-bromomalodinitrile concentration-dependent increase. The gradual decrease in the reoxidation capacity of the reduced quencher, Q with increasing α-benzyl-α-bromomalodinitrile concentrations provides evidence for an additional inhibitory site for α-benzyl-α-bromomalodinitrile between the two photosystems.     

Comparative labelling of α1-acid glycoprotein by (3H)-borohydride or (125I)-iodide for use in a radioimmunoassay

The labelling of α₁-acid glycoprotein (AGP) with (³H)-sodium borohydride was compared to the labelling with (¹²⁵I)-sodium iodide by the chloramine T method in view to its use in a radioimmunoassay. The tritium labelling allowed to reach a high specific radioactivity similar to that obtained with iodide ((³H)-AGP: 29.8 mCi/mg; (¹²⁵I)-AGP: 30.5 mCi/mg). Each mole of sialic acid residue of AGP contains one atom of tritium. The stability of (³H)-AGP was better than that of (¹²⁵I)-AGP as indicated by its immunoreactivity as a function of time. Immunoreactivities and standard curves were similar for the two tracers but affinity of antiserum was higher for (¹²⁵I)-AGP than for (³H)-AGP. Tritium labelling by (³H)-borohydride will be very useful for glycoprotein antigens which cannot be labelled with (¹²⁵I)-iodide.     

Length polymorphism in the pro α2(I) collagen gene: an alternative explanation in a case of Marfan syndrome

Summary A 38 base pair (bp) insertion in the pro 2(I) collagen gene (COL1A2) of a patient with Marfan syndrome has been proposed to be the possible cause of the disease (Henke et al. 1985). However, analysis of this insertion in DNA from the patient in question and from random normal individuals reveals it to be a common polymorphism. We suggest that the 38 bp insertion is not related to the primary defect in this case of Marfan syndrome.     

Microlocating lithium in the mouse embryo by use of a (n, α) nuclear reaction

Summary The quantitative imaging of lithium distribution, in histological sections of 15-days old mouse embryos (whose mother had been submitted to Li-treatment), was performed using⁶Li isotope as tracer,⁶Li(n,)³H nuclear reaction for detection, and dielectric track detectors. Despite the particular difficulties of cryosectioning the embryos without disturbing the lithium distribution, the Li regionalization appeared to be very clear-cut. The ectomesodermic tissues were significantly more loaded with lithium than the endodermic ones. This is probably related to the ectomesodermic tissues being also those most sensitive to the teratogenic effect of lithium. The Li-distribution in the embryo brain was almost homogeneous, instead of being heterogeneous as in adult brain. The mean Li-concentration in the embryo brain was not much below the Li concentration in the grey matter of the mother brain, but it was significantly larger than that in the white matter of the mother brain. Our results are discussed in the context of teratogenic effects observed in situ during mammalian development.     

Roles for the two N-terminal (β/α) modules in the folding of a (β/α)₈-barrel protein as studied by fragmentation analysis

The (β/α)₈‐barrel is one of the most abundant folds found in enzymes. To identify the independent folding units and the segment(s) that correspond to a minimum core structure within a (β/α)₈‐barrel protein, fragmentation experiments were performed with Escherichia coli phosphoribosylanthranilate isomerase, which has a single (β/α)₈‐barrel domain. Our previous studies indicated that the central four β/α segments comprise an independent folding unit; whereas, the role(s) of the first two β/α segments in folding had not been clarified prior to this report. Herein, we report the design and synthesis of a series of N‐terminally deleted fragments starting with (β/α)_1–5β₆ as the parent construct. Analytical gel filtration and urea‐induced equilibrium unfolding experiments indicated that deletions within the N‐terminal region, that is, within the first two β/α modules, resulted in reduced stability or aggregation of the remaining segments. The (β/α)_3–5β₆ segment appeared to fold into a stable structure and deletion of β₆ from (β/α)_3–5β₆ yielded (β/α)_3–5, which did not form native‐like secondary structures. However, urea‐induced unfolding of (β/α)_3–5, monitored by reduction of tryptophan fluorescence, indicated that the fragment contained a loosely packed hydrophobic core. Taken together, the results of our previous and present fragmentation experiments suggest the importance of the central (β/α)_3–4β₅ module in folding, which is a finding that is compatible with our simulated unfolding study performed previously. Proteins 2010. © 2010 Wiley‐Liss, Inc.     

Rotational diffusion of the α(2a) adrenergic receptor revealed by FlAsH labeling in living cells

The fluorescein arsenical hairpin binder (FlAsH) shows much promise to determine the relative orientations of protein regions and structures even in living cells and in the plasma membrane. In this study, we characterized FlAsH's photophysical properties by steady-state anisotropy and time-resolved single photon counting for further applications with G-protein coupled receptors. We find that FlAsH has a relatively high initial anisotropy of 0.31 ± 0.01 and a three-component fluorescence lifetime with an average of 4.1 ± 0.1 ns. We characterized the FlAsH fluorophore orientation in the α(2A) adrenergic receptor revealing rigid orientations of FlAsH in the membrane plane for rotational correlation times of ～50 ns in living cells. To elucidate the fluorophore-membrane orientation and rotational correlation time, an anisotropy treatment similar to that of another researcher (Axelrod, D. 1979. Biophys. J. 26:557-573) was developed. The rotational correlation times were observed to increase by up to 16 ns after agonist addition. The rotational correlation time also allowed for a comparison to the theoretical relationship between translational and rotational diffusion (originally proposed by Saffman, P. G., and M. Delbrück. 1975. Proc. Natl. Acad. Sci. USA. 72:3111-3113) and revealed a discrepancy of a factor between 10 and 100.     

The Expression of Tumor Necrosis Factor-α (TNF-α) by the Intrathecal Injection of Lipopolysaccharide in the Rat Spinal Cord

The proinflammatory and lipopolysaccharide (LPS)-inducible cytokine tumor necrosis factor α (TNF-α) has been shown to enhance primary sensory nociceptive signaling. However, the precise cellular site of TNF-α synthesis is still a matter of controversy. Therefore, we focused our study on TNF-α protein synthesis and expression patterns in spinal dorsal horn of naives and rats under intrathecal challenge with LPS. The enzyme-linked immunosorbent (ELISA) assay showed that the protein level of TNF-α reached peak at 8 h. Double immunofluorescence revealed that LPS-induced expression of TNF-α exclusively located in a subpopulation of microglia, which increased at 8 h in the rat spinal dorsal horn (the injected side). Positive staining of TNF receptor 1 (TNFR1) were also found in microglia. These observations have demonstrated the production of this proinflammatory cytokine by central nerve glia especially microglia. Synthesized TNF-α might directly act on microglia via TNFR1, but the inherent mechanisms remain unknown. Further studies are needed to confirm the pathogenic role of tumor necrosis factor in the early stage of inflammation. Aiguo Shen and Dan Zhou contributed equally to this work.     

Crystal structure of α-1,3-galactosyltransferase (α3GT) in a complex with p-nitrophenyl-β-galactoside (pNPβGal)

The specificities of glycosyltransferases make them useful for the synthesis of biologically active oligosaccharides, but also restrict their range of products. In substrate engineering, substrate promiscuity is enhanced by attaching removable interactive groups to weak substrates. Thus, the attachment of β p-nitrophenyl converts galactose from a poor into a good substrate of α-1,3-galactosyltransferase. The crystallographic structure of a complex of α3GT containing p-nitrophenyl-β-galactoside shows that the p-nitrophenyl binds similarly to the N-acetylglucosamine of the substrate, N-acetyllactosamine, interacting with the indole of Trp249. p-Nitrophenyl, unlike N-acetylglucosamine, makes no H-bonds but has more non-polar interactions, making it an effective monosaccharide mimetic.