111. THE ROLE OF L-PROLINE IN PREIMPLANTATION MOUSE EMBRYO DEVELOPMENT IN VITRO

Amino acids are known to play important roles in preimplantation embryo development, including regulation of cell volume and metabolism. Inclusion of l-glutamine, glycine and betaine in embryo culture medium has been shown to improve development in vitro by acting as organic osmolytes, thereby regulating cell volume. The purpose of the present study was to examine the effect of l-proline on preimplantation mouse embryo development in vitro. One-cell stage embryos were cultured in modified HTF, at low density (1 embryo/100 μL) and high density (1 embryo/μL) in the presence and absence of amino acids. Development of the embryos was scored every 24 h until the blastocyst stage. At low density, l-proline significantly increased the proportion of embryos developing to the blastocyst stage. This effect was abolished by culture at high density, suggesting that l-proline was activating a pathway similar to that involved in autocrine signalling by trophic factors in the preimplantation embryo. The improvement in development observed in the presence of l-proline was not due to its action as an organic osmolyte since the osmolality of the medium was 270 mOsm. Furthermore, glycine and betaine, which are known to act as osmolytes in embryos, had no effect on blastocyst development. In embryonic stem cells L-proline is taken up by an amino acid transporter and is involved in the regulation of growth and differentiation (1). The present data suggest that l-proline may have a similar, important role in preimplantation development. (1) JM Washington, J Rathjen, F Felquer, A Lonic, MD Bettess, N Hamra, L Semendric, BSN Tan, J-A Lake, RA Keough, MB Morris and PD Rathjen (2010) Am J Physiol Cell Physiol 298: C982–C992.

182. NOVEL SIGNALLING IN MOUSE EMBRYONIC STEM CELLS GENERATES PRIMITIVE ECTODERM-LIKE CELLS

The phenotypic status of embryonic stem (ES) cells is controlled in part by signalling pathways which translate inputs mediated by extracellular molecules. An important extracellular protagonist in mouse ES cells is LIF (leukaemia inhibitory factor) which interacts with the gp130–LIFR receptor complex to activate a number of downstream signalling pathways, including the STAT3, MEK/ERK and PI3K/Akt. These pathways, together with others, interact in complex and sometimes competing ways to generate the well-known characteristics of mouse ES cells of self-renewal, high rates of proliferation, and pluripotence. The addition of a second molecule, L-proline, to the extracellular environment alters the pluripotent status of mouse ES cells, converting them to a second pluripotent population equivalent to the primitive ectoderm of the pre-gastrulating embryo. This conversion, from ES cells to primitive ectoderm-like cells, primes the latter for directed differentiation to specific cell types (1). Here we show, using inhibitor studies and kinome array analysis, that this small molecule appears to work by (i) changing the balance in activity of signalling pathways already stimulated by LIF and (ii) activating additional signalling pathways. Specifically, L-proline rapidly further activates the LIF-stimulated MEK/ERK pathway, tipping the balance in favour of primitive-ectoderm formation and away from ES-cell self-renewal sustained by LIF-mediated activation of the STAT3 pathway. In addition, L-proline rapidly stimulates other pathways including p38, mTOR and PI3K/Akt each of which contributes, to a greater or lesser extent, to the conversion to primitive ectoderm-like cells. These results indicate that (i) L-proline acts in novel ways to stimulate embryo-like developmental progression in ES cells and (ii) through the addition of small, nontoxic activators and inhibitors of signalling pathways, the differentiation of pluripotent ES cells might be controlled sufficiently well for the homogeneous production of specific cell types suitable for use in animal models of human disease.

Selective modulation of P-glycoprotein-mediated drug resistance

Multidrug resistance associated with the overexpression of the multidrug transporter P-glycoprotein is a serious impediment to successful cancer treatment. We found that verapamil reversed resistance of CEM/VLB(100) cells to vinblastine and fluorescein-colchicine, but not to colchicine. Chlorpromazine reversed resistance to vinblastine but not to fluorescein-colchicine, and it increased resistance to colchicine. Initial influx rates of fluorescein-colchicine were similar in resistant and parental cells, whereas vinblastine uptake was about 10-fold lower in the resistant cells. These results provide indirect evidence that fluorescein-colchicine is transported from the inner leaflet of the membrane and vinblastine from the outer membrane leaflet. Verapamil inhibited fluorescein-colchicine transport in inside-out vesicles made from resistant cells, whilst chlorpromazine was found to activate the transport of fluorescein-colchicine. The chlorpromazine-induced activation of fluorescein-colchicine transport was temperature-dependent and may reflect its interaction with phospholipids localised in the same bilayer leaflet. Conversely, chlorpromazine localisation in this leaflet may be responsible for its allosteric inhibition of vinblastine transport from the opposing membrane leaflet. The proposed relationship between the selectivity of modulation of P-glycoprotein and the membrane localisation of the cytotoxic drug substrates and modulators may have important implications in the rational design of regimes for the circumvention of multidrug resistance clinically.

Modeling of the structural features of integral-membrane proteins reverse-environment prediction of integral membrane protein structure (REPIMPS)

The Profiles-3D application, an inverse-folding methodology appropriate for water-soluble proteins, has been modified to allow the determination of structural properties of integral-membrane proteins (IMPs) and for testing the validity of solved and model structures of IMPs. The modification, known as reverse-environment prediction of integral membrane protein structure (REPIMPS), takes into account the fact that exposed areas of side chains for many residues in IMPs are in contact with lipid and not the aqueous phase. This (1) allows lipid-exposed residues to be classified into the correct physicochemical environment class, (2) significantly improves compatibility scores for IMPs whose structures have been solved, and (3) reduces the possibility of rejecting a three-dimensional structure for an IMP because the presence of lipid was not included. Validation tests of REPIMPS showed that it (1) can locate the transmembrane domain of IMPs with single transmembrane helices more frequently than a range of other methodologies, (2) can rotationally orient transmembrane helices with respect to the lipid environment and surrounding helices in IMPs with multiple transmembrane helices, and (3) has the potential to accurately locate transmembrane domains in IMPs with multiple transmembrane helices. We conclude that correcting for the presence of the lipid environment surrounding the transmembrane segments of IMPs is an essential step for reasonable modeling and verification of the three-dimensional structures of these proteins.

IgM expressed by leukemic CD5(+) B cells binds mouse immunoglobulin light chain

Mouse immunoglobulin (Ig) molecules have previously been shown to bind to the surface of CD5(+) B cells from patients with B-cell chronic lymphocytic leukemia (B-CLL). The results indicated that surface IgM was involved in the interaction and suggested the phenomenon was an example of the polyreactive binding capacity of the surface Ig (sIg) expressed by these malignant cells. This article describes the further characterization of the interaction between human IgM and mouse Ig molecules and subunits. Mouse Ig molecules of both kappa and lambda light chain classes bound to the B-CLL cell surface. The dissociation constant for the interaction of mouse IgG1 (K121) with the B-CLL cell surface was 3.6 x 10(-7) M. To confirm the involvement of the human IgM expressed by the B-CLL cells in the interaction, the malignant cells were stimulated in vitro to induce secretion of human IgM. Enzyme immunoassay was used to show that secreted human IgM bound to intact mouse Ig, as occurred with the cell surface analysis. The mouse Ig epitope recognized by the purified secreted human IgM was shown by Western blot analysis to be located on the light chain of the mouse Ig molecule and to be conformationally dependent. K121 light chain was cloned and expressed in E. coli and the recombinant light chain bound to the surface of CLL B cells. The results confirm that human IgM is the reactive ligand in the interaction with mouse Ig and indicate that the interaction of polyreactive IgM with mouse IgG occurs via the light chain component of IgG.

Thermodynamic and Hydrodynamic Properties of Human Tropoelastin

Tropoelastin is the soluble precursor of elastin that bestows tissue elasticity in vertebrates. Tropoelastin is soluble at 20 degrees C in phosphate-buffered saline, pH 7.4, but at 37 degrees C equilibrium is established between soluble protein and insoluble coacervate. Sedimentation equilibrium studies performed before (20 degrees C) and after (37 degrees C) coacervation showed that the soluble component was strictly monomeric. Sedimentation velocity experiments revealed that at both temperatures soluble tropoelastin exists as two independently sedimenting monomeric species present in approximately equal concentrations. Species 1 had a frictional ratio at both temperatures of approximately 2.2, suggesting a very highly expanded or asymmetric protein. Species 2 displayed a frictional ratio at 20 degrees C of 1.4 that increased to 1.7 at 37 degrees C, indicating a compact and symmetrical conformation that expanded or became asymmetric at the higher temperature. The slow interconversion of the two monomeric species contrasts with the rapid and reversible process of coacervation suggesting both efficiently incorporate into the coacervate. A hydrated protein of equivalent molecular weight modeled as a sphere and a flexible chain was predicted to have a frictional ratio of 1.2 and 1.6, respectively. Tropoelastin appeared as a single species when studied by pulsed field-gradient spin-echo NMR, but computer modeling showed that the method was insensitive to the presence of two species of equal concentration having similar diffusion coefficients. Scintillation proximity assays using radiolabeled tropoelastin and sedimentation analysis showed that the coacervation at 37 degrees C was a highly cooperative monomer-n-mer self-association. A critical concentration of 3.4 g/liter was obtained when the coacervate was modeled as a helical polymer formed from the monomers via oligomeric intermediates.

Extracellular ATP-dependent suppression of proliferation and induction of differentiation of human HL-60 leukemia cells by distinct mechanisms

Extracellular ATP suppressed the growth of HL-60 leukemia cells and induced their differentiation as revealed by N-formyl-methionyl-leucyl-phenylalanine-induced beta-glucuronidase release. ATP degraded to ADP, AMP, and adenosine, and the effect of ATP on cell growth was mimicked by these metabolites added to the cultures. The stable analog alpha,beta-methylene ATP, however, had only a weak inhibitory effect on cell growth. Adenine nucleotide-induced growth suppression was reversed by uridine, suggesting the involvement of intracellular pyrimidine starvation secondary to adenosine accumulation. Consistent with this, ATP induced intracellular starvation of pyrimidine nucleotides, and this effect was also prevented by pretreatment of cells with uridine. The order of effectiveness of ATP-induced differentiation of HL-60 cells, unlike that for growth suppression, was ATP > ADP > AMP, and adenosine had no effect. Furthermore, uridine had no effect and the stable analog, alpha,beta-methylene ATP also induced HL-60 cell differentiation, suggesting that differentiation was due to ATP per se. We tested the hypothesis that ATP-induced differentiation arises from activation of adenylyl cyclase by the novel P2Y(11) receptor using the cell-permeable inhibitor of protein kinase A, Rp-CPT-cAMPS (8-(4-chlorophenylthio)adenosine-3',5'-cyclic monophosphorothioate, Rp isomer). Rp-CPT-cAMPS (1-100 microM) prevented ATP-induced differentiation of HL-60 cells as assessed by fMLP-induced beta-glucuronidase release. However, Rp-CPT-cAMPS did not prevent ATP-induced growth suppression. Taken together, the data indicate that extracellular ATP suppresses HL-60 growth and induces their differentiation by distinct mechanisms. Growth suppression arises from adenosine generation and consequent pyrimidine starvation. Differentiation arises, at least in part, from a distinct mechanism involving the activation of cell surface P2 receptors coupled to cAMP generation and activation of protein kinase A.

Acid denaturation of recombinant porcine growth hormone: formation and self-association of folding intermediates

We have investigated the conformational changes incurred during the acid-induced unfolding and self-association of recombinant porcine growth hormone (pGH). Acidification (pH 8 to pH 2) of pGH resulted in intrinsic fluorescence, UV absorbance, and near-UV CD transitions centered at pH 4.10. At pH 2.0, a red shift in the fluorescence emission maximum of approximately 3 nm and a 15% loss of the far-UV CD signal at 222 nm imply that the protein did not become extensively unfolded. Acidification in the presence of 4 M urea resulted in similar pH-dependent transitions. However, these occurred at a higher pH (approximately 5.2). At pH 2.0 + 4 M urea, an 8 nm red shift in the fluorescence emission maximum suggests that unfolding was greater than in the absence of urea. The presence of a prominent peak centered at 298 nm in the near-UV CD spectrum, which is absent without urea, signifies further differences in the intermediates generated at pH 2. Sedimentation equilibrium experiments in the analytical ultracentrifuge showed that native pGH and the partially unfolded intermediates reversibly self-associate. Self-association was strongly promoted at pH 2 while urea reduced self-association at both pH 8 and pH 2. These results demonstrate that acidification of pGH in the absence or presence of 4 M urea induced the formation of molten globule-like states with measurable differences in conformation. Similarities and differences in these structural conformations with respect to other growth hormones are discussed.

Extracellular ATP couples to cAMP generation and granulocytic differentiation in human NB4 promyelocytic leukaemia cells

Priming of NB4 promyelocytic cells with all-trans retinoic acid, followed by extracellular ATP in the presence of a phosphodiesterase inhibitor, elevated cAMP and activated protein kinase A. The order of potency for cAMP production was ATP (EC50 = 95 +/- 13 micromol/L) > ADP > AMP = adenosine. The order of potency of ATP analogues was 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (EC50 = 54 +/- 15 micromol/L) = adenosine 5'-O-(3-thio) triphosphate (EC50 = 66 +/- 4 micromol/L) > ATP > beta,gamma-methylene ATP (EC50 = 200 +/- 55 micromol/L). Adenosine 5'-O-thiomonophosphate and adenosine 5'-O-(2-thio) diphosphate inhibited ATP-induced cAMP production. Differentiation also occurred as measured by increased expression of CD11b and N-formyl peptide receptor and changes in cell morphology. UTP did not elevate cAMP or induce differentiation, indicating that P2Y2, P2Y4, and P2Y6 receptors were not involved. The P2Y11 receptor, a cAMP-linked receptor on promyelocytic HL-60 cells, was detected in NB4 cells by reverse transcription-polymerase chain reaction and northern blotting. This receptor has the same order of potency with respect to cAMP production as that observed in HL-60 cells.

Pharmacological characterisation of the P2Y11 receptor in stably transfected haematological cell lines

The recently cloned P2Y11 receptor is unique amongst P2Y receptors with its coupling to the adenylyl cyclase pathway. P2Y11 has previously been shown to be expressed in human acute promyelocytic leukemia (APL) HL-60 and NB4 cell lines, and both cell types elevate cyclic AMP (cAMP) levels upon stimulation with extracellular ATP. Acute erythroleukemic K562 cells and acute monocytic leukemia U937 cells did not elevate cAMP levels upon exposure to 1 mM extracellular ATP. However, K562 and U937 cells stably transfected with P2Y11 (K11 and U11 cells, respectively) were responsive to extracellular ATP, with an EC50 of 31 and 21 microM, respectively. The most potent agonists in both K11 and U11 cells were ATPgammaS (adenosine 5'-O-[3-thiotriphosphate]), ATPalphaS (adenosine 5'-O-[1-thiotriphosphate]), dATP and ADPbetaS (adenosine 5'-O-[2-thiobisphosphate]), which were of similar or greater potency compared to ATP itself. ADP and alpha,beta-methylene ATP were less potent compared to ATP. The order of potency for ATP breakdown products was ATP > ADP > AMP > or = Ado. UTP, a known activator of P2Y2 and P2Y4, was largely ineffective. In the transfected cells, ATP-induced cAMP elevation was inhibited by suramin (0.5 mM), but not XAC (20 microM) nor PPADS (100 microM). AMPS inhibited ATP-induced cAMP elevation in both K11 and U11 cells (EC50 approximately 3 mM) and may be a P2Y11-selective inhibitor. These results are similar to those observed for HL-60 cells and NB4 cells implicating P2Y11 as the receptor responsible for the ATP-induced cAMP elevations in these cells.

Signal transduction and white cell maturation via extracellular ATP and the P2Y11 receptor

Extracellular ATP promotes a wide range of physiological effects in many tissues. Of particular interest is the effect of ATP on leukaemia-derived HL-60 and NB4 cell lines, which are induced to mature to neutrophil-like cells. The differentiation process appears to be mediated by ATP binding to a cell-surface purinergic P2Y receptor, resulting in the stimulation of adenylyl cyclase, elevation of cAMP levels and activation of protein kinase A. In 1997, a novel ATP-selective P2Y receptor, P2Y11, was cloned and shown to be linked to both cAMP and Ca2+ signalling pathways. The pharmacological profile of ATP analogues used by P2Y11 for cAMP production in transfected cells is reviewed in the present paper and shown to be closely similar to the profiles for cAMP production and differentiation of myeloblastic HL-60 cells and promyelocytic NB4 cells, both of which express P2Y11. Additional data are provided showing that HL-60 mature to neutrophil-like cells in response to extracellular ATP, as measured by upregulation of the N-formyl peptide receptor, N-formyl peptide-mediated actin polymerization and superoxide production. It is proposed that P2Y11 is responsible for the ATP-mediated differentiation of these cells lines and that this receptor may play a role in the maturation of granulocytic progenitors in the bone marrow.

Initiation of spectrin dimerization involves complementary electrostatic interactions between paired triple-helical bundles

The spectrin heterodimer is formed by the antiparallel lateral association of an alpha and a beta subunit, each of which comprises largely a series of homologous triple-helical motifs. Initiation of dimer assembly involves strong binding between complementary motifs near the actin-binding end of the dimer. In this study, the mechanism of lateral spectrin association at this dimer nucleation site was investigated using the analytical ultracentrifuge to analyze heterodimers formed from recombinant peptides containing two or four homologous motifs from each subunit (alpha20-21/beta1-2; alpha18-21/beta1-4). Both the two-motif and four-motif dimer associations were weakened substantially with increasing salt concentration, indicating that electrostatic interactions are important for the dimer initiation process. Modeling of the electrostatic potential on the surface of the alpha20 and beta2 motifs showed that the side of the motifs comprising the A and B helices is the most favorable for association, with an area of positive electrostatic potential on the AB face of the beta2 motif opposite negative potential on the AB face of the alpha20 motif and vise versa. Protease protection analysis of the alpha20-21/beta1-2 dimer showed that multiple trypsin and proteinase K sites in the A helices of the beta2 and alpha21 motifs become buried upon dimer formation. Together, these data support a model where complementary long range electrostatic interactions on the AB faces of the triple-helical motifs in the dimer nucleation site initiate the correct pairing of motifs, i.e. alpha21-beta1 and alpha20-beta2. After initial docking of these complementary triple-helical motifs, this association is probably stabilized by subsequent formation of stronger hydrophobic interactions in a complex involving the A helices of both subunits and possibly most of the AB faces. The beta subunit A helix in particular appears to be buried in the dimer interface.

A continuous fluorescence assay for the study of P-glycoprotein-mediated drug efflux using inside-out membrane vesicles

A fluorimetric procedure for assaying the transport activity of P-glycoprotein (P-gp) using a membrane vesicle model has been developed. In this assay methylene blue is incorporated into inside-out vesicles prepared from human acute lymphoblastic leukemic cells resistant to 100 ng. ml-1 vinblastine (VBL100) and their sensitive controls. The fluorescence of a fluorescent derivative of colchicine (fluorescein-colchicine) is quenched as the probe is transported across the vesicle membrane. The fluorescein-colchicine transport was found to be dependent on the presence of P-glycoprotein, required ATP, and was inhibited by vanadate and the reversal agent, verapamil, in a dose-dependent manner. Furthermore, the transport was competed against by the P-gp substrates, vinblastine and methotrexate. The transport of fluorescein-colchicine by P-gp was found to be cooperative (n = 1. 23). The assay is rapid, requires small amounts of sample, and removes the need for the radioactive procedures used in the past. The assay should find use in characterizing the transport kinetics of P-gp, for examining and optimizing combinations of chemotherapeutics, and for examining the effects of reversal agents and substrates which potentially compete for transport with the fluorescent substrate probe. Other possible applications include examining P-gp-mediated transport properties of purified P-gp in reconstituted systems.

Pharmacological profile of a novel cyclic AMP-linked P2 receptor on undifferentiated HL-60 leukemia cells

1. Extracellular ATP (EC50=146+/-57 microM) and various ATP analogues activated cyclic AMP production in undifferentiated HL-60 cells. 2. The order of agonist potency was: ATPgammaS (adenosine 5'-O-[3-thiotriphosphate]) > or = BzATP (2'&3'O-(4-benzoylbenzoyl)-adenosine-5'-triphosphate) > or = dATP > ATP. The following agonists (in order of effectiveness at 1 mM) were all less effective than ATP at concentrations up to 1 mM: beta,gamma methylene ATP > or = 2-methylthioATP > ADP > or = Ap4A (P1, P4-di(adenosine-5') tetraphosphate) > or = Adenosine > UTP. The poor response to UTP indicates that P2Y2 receptors are not responsible for ATP-dependent activation of adenylyl cyclase. 3. Several thiophosphorylated analogs of ATP were more potent activators of cyclic AMP production than ATP. Of these, ATPgammaS (EC50=30.4+/-6.9 microM) was a full agonist. However, adenosine 5'-O-[1-thiotriphosphate] (ATPalphaS; EC50=45+/-15 microM) and adenosine 5'-O-[2-thiodiphosphate] (ADPbetaS; EC50=33.3+/-5.0 microM) were partial agonists. 4. ADPbetaS (IC50=146+/-32 microM) and adenosine 5'-O-thiomonophosphate (AMPS; IC50=343+/-142 microM) inhibited cyclic AMP production by a submaximal concentration of ATP (100 microM). Consistent with its partial agonist activity, ADPbetaS was estimated to maximally suppress ATP-induced cyclic AMP production by about 65%. AMPS has not been previously reported to inhibit P2 receptors. 5. The broad spectrum P2 receptor antagonist, suramin (500 microM), abolished ATP-stimulated cyclic AMP production by HL-60 cells but the adenosine receptor antagonists xanthine amine congener (XAC; 20 microM) and 8-sulpho-phenyltheophylline (8-SPT; 100 microM) were without effect. 6. Extracellular ATP also activated protein kinase A (PK-A) consistent with previous findings that PK-A activation is involved in ATP-induced differentiation of HL-60 cells (Jiang et al., 1997). 7. Taken together, the data indicate the presence of a novel cyclic AMP-linked P2 receptor on undifferentiated HL-60 cells.

Biophysical properties of human erythrocyte spectrin at alkaline pH: implications for spectrin structure, function, and association

The effects of pH 6-13 on the conformation and assembly of spectrin were studied by means of analytical ultracentrifugation, circular dichroism (CD), 1H NMR, and UV spectrophotometry. Sedimentation velocity analysis showed that spectrin oligomers dissociate cooperatively into component alpha- and beta-subunits above pH 9.5, and that spectrin tetramers, heterodimers, and monomers adopt more extended and/or expanded shapes above this pH. The dissociation to monomers is mostly completed by pH 10.5 and is used as the basis for purifying the subunits [see Fujita et al. (1998) Biochemistry 37, 272-280]. Along with the dissociation, biphasic unfolding of spectrin was observed above pH 9.5 as detected by CD. The first phase of the transition occurred between pH 9.5 and 11, and the second phase between pH 11 and 13. A similar biphasic dependence was observed for the upfield shift of lysine epsilon-CH2 resonances detected by spin-echo 1H NMR and the spectrophotometric titration of the absorbance at 294 nm. These data indicate that deprotonation of tyrosine and lysine residues is closely correlated with (i) the dissociation of spectrin oligomers into heterodimers, (ii) the dissociation of heterodimers into monomers, and (iii) the unfolding of spectrin. Taken together, our data suggest that hydrophobic and electrostatic interactions involving tyrosine and lysine residues play a critical role in the formation of the alpha-helix of spectrin and assembly of physiologically relevant spectrin oligomers from the two component subunits.

Purification of erythrocyte spectrin alpha- and beta-subunits at alkaline pH and structural and hydrodynamic properties of the isolated subunits

A new method for the isolation of the alpha- and beta-subunits of human erythrocyte spectrin was developed, and structural properties and association behavior of the isolated subunits were studied by means of CD, nondenaturing gel electrophoresis, and analytical ultracentrifugation. The alpha- and beta-subunits were isolated using ion-exchange FPLC (pH 11) followed by size-exclusion FPLC (pH 7.5), having shown that alkaline pH dissociates spectrin polymers to their monomers [see Fujita et al. (1998) Biochemistry 37, 264-271]. The isolated subunits had alpha-helical content and thermal stability almost equivalent to those of native spectrin and reassembled to form heterodimers and tetramers which were indistinguishable from native spectrin with respect to secondary structure content, thermal stability, migration pattern on nondenaturing gels, and sedimentation coefficients. Thus, our data show that the increase in the structural stability of a heterodimer by association of the two monomers is very small. Sedimentation coefficients for the isolated alpha- and beta-subunits were 6.3 and 5.7 S, respectively. The similar frictional ratios (f/f0) of the isolated alpha-subunit (2.42) and the beta-subunit (2.45) indicate that the flexibility of both these wormlike chains and the range of shapes they can adopt in solution are very similar. The f/f0 value for spectrin dimer (2.41) indicates that its flexibility is somewhat, but not grossly, reduced compared to that of the individual subunits. Consequently, the folded repeat units of the subunits and the flexible connections between them are probably "in register" along the length of the dimer.

The subunit delta-subunit b domain of the Escherichia coli F1F0 ATPase. The B subunits interact with F1 as a dimer and through the delta subunit

The delta and b subunits are both involved in binding the F1 to the F0 part in the Escherichia coli ATP synthase (ECF1F0). The interaction of the purified delta subunit and the isolated hydrophilic domain of the b subunit (bsol) has been studied here. Purified delta binds to bsol weakly in solution, as indicated by NMR studies and protease protection experiments. On F1, i.e. in the presence of ECF1-delta, delta, and bsol interact strongly, and a complex of ECF1.bsol can be isolated by native gel electrophoresis. Both delta subunit and bsol are protected from trypsin cleavage in this complex. In contrast, the delta subunit is rapidly degraded by the protease when bound to ECF1 when bsol is absent. The interaction of bsol with ECF1 involves the C-terminal domain of delta as delta(1-134) cannot replace intact delta in the binding experiments. As purified, bsol is a stable dimer with 80% alpha helix. A monomeric form of bsol can be obtained by introducing the mutation A128D (Howitt, S. M., Rodgers, A. J.,W., Jeffrey, P. D., and Cox, G. B. (1996) J. Biol. Chem. 271, 7038-7042). Monomeric bsol has less alpha helix, i.e. only 58%, is much more sensitive to trypsin cleavage than dimer, and unfolds at much lower temperatures than the dimer in circular dichroism melting studies, indicating a less stable structure. The bsol dimer, but not monomer, binds to delta in ECF1. To examine whether subunit b is a monomor or dimer in intact ECF1F0, CuCl2 was used to induce cross-link formation in the mutants bS60C, bQ104C, bA128C, bG131C, and bS146C. With the exception of bS60C, CuCl2 treatment resulted in formation of b subunit dimers in all mutants. Cross-linking yield was independent of nucleotide conditions and did not affect ATPase activity. These results show the b subunit to be dimeric for a large portion of the C terminus, with residues 124-131 likely forming a pair of parallel alpha helices.

Comparison of the salt-dependent self-association of brain and erythroid spectrin

The self-association of ovine brain spectrin in 0.1-1.5 M NaCl (pH 7.5) was studied using sedimentation velocity and sedimentation equilibrium techniques. Brain spectrin is tetrameric at sedimentation equilibrium at a 0.13 M ionic strength at 18-37 degrees C and at ionic strengths of up to 0.33 M at 20 degrees C. At ionic strengths greater than 0.33 M at 20 degrees C, the brain spectrin tetramer is destabilized, resulting in both dissociation to dimers and indefinite association to higher oligomers, in a manner similar to that seen with erythroid spectrin. The equilibrium constants describing all steps in the association involving the addition of dimers are around 15-fold higher for brain spectrin than for erythroid spectrin, at ionic strengths of > or = 0.43 M. We propose that the stronger association of brain spectrin compared to that of erythroid spectrin is due to a relative inability of brain spectrin to form closed dimers. Sedimentation velocity analysis confirms that brain spectrin readily forms open dimers and that the association of open dimers is not kinetically trapped even at 2 degrees C. Our results suggest that the destabilization of spectrin tetramers in high-ionic strength conditions is due to increased independent movement of the alpha and beta subunits resulting from disruption of electrostatic interactions. The greater stability of brain spectrin oligomers relative to those of erythroid spectrin is due to stronger nonelectrostatic interactions which stabilize the rigidity of the individual subunits and thereby increase the conformational strain associated with dimer closure.

Measuring protein self-association using pulsed-field-gradient NMR spectroscopy: application to myosin light chain 2

At the millimolar concentrations required for structural studies, NMR spectra of the calcium-binding protein myosin light chain 2 (MLC2) showed resonance line widths indicative of extensive self-association. Pulsed-field-gradient (PFG) NMR spectroscopy was used to examine whether MLC2 aggregation could be prevented by the zwitterionic bile salt derivative 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS). PFG NMR measurements indicated that CHAPS was capable of preventing MLC2 self-association, but only at concentrations well above the critical micelle concentration of approximately 7.5 mM. CHAPS was most effective at a concentration of 22.5 mM, where the apparent molecular mass of MLC2 corresponded to a protein monomer plus seven molecules of bound detergent. The resolution and sensitivity of 2D 15N-1H HSQC spectra of MLC2 were markedly improved by the addition of 25 mM CHAPS, consistent with a reduction in aggregation following addition of the detergent. The average amide nitrogen T2 value for MLC2 increased from approximately 30 ms in the absence of CHAPS to approximately 56 ms in the presence of 25 mM CHAPS. The results of this study lead us to propose that PFG NMR spectroscopy can be used as a facile alternative to conventional techniques such as analytical ultracentrifugation for examining the self-association of biological macromolecules.

Characterization of the binary interaction between human erythrocyte protein 4.1 and actin

The binary interaction between human erythrocyte protein 4.1 and rabbit skeletal muscle F-actin was examined by rapid pelleting of the binary complexes. The binding curves show that the reaction was saturable at approximately one protein 4.1 molecule/actin monomer. The reaction was highly co-operative, displaying a Hill coefficient close to 2. Using a fixed concentration of radiolabelled protein 4.1, and varying the concentration of F-actin, the apparent molar association constant, Ka, was observed to range from 5 x 10(4) M-1 to > 10(6) M-1. The binary interaction between erythrocyte spectrin and actin was also observed to be co-operative under the same conditions. The rate of reaction between protein 4.1 and actin was temperature sensitive in a manner consistent with a high energy of activation. The pelleting assay also showed that the concentration of actin was reduced in the supernatant in the presence of protein 4.1 compared with actin alone, indicating that the critical concentration of actin was lowered in the presence of protein 4.1. Polyvalent anions disrupted the binary interaction between F-actin and protein 4.1, the disruption being consistent with the number of negative charges on these anions at pH 7.5. We postulate that the co-operativity of the binding of protein 4.1 to actin results from a protein 4.1 molecule binding to a single monomer within the filament structure which then promotes conformational changes allowing further protein 4.1 binding. The demonstration of a specific binary association between protein 4.1 and actin suggests that this interaction contributes significantly to the stabilization of the spectrin-actin-protein-4.1 ternary complex.

Structural and biochemical studies of human galanin: NMR evidence for nascent helical structures in aqueous solution

The 30-residue human neuropeptide, galanin, was shown to bind to rat insulinoma RINm5F cells and to inhibit glyceraldehyde-stimulated insulin secretion from these cells in a manner quantitatively similar to that of porcine galanin. Neither human nor porcine galanin stimulated Ca2+ mobilization in cultured human small cell lung carcinoma cells. Sedimentation equilibrium analysis of human galanin showed that it was strictly monomeric in aqueous solution, indicating that the peptide interacts with its receptor(s) as a monomer. The monomeric nature of the peptide makes it especially suitable for structural studies using NMR. Nuclear Overhauser enhancement spectroscopy experiments performed on galanin dissolved in aqueous solution (150 mM KCl, pH 4) at both 33 and 3 degrees C indicate that certain regions of the peptide are capable of adopting detectable levels of short-range structure in rapid equilibrium with random coil. At 33 degrees C, the short-range structures include a nascent helix spanning residues 3-11 which incorporates a hydrophobic core from residues 6-11. Residues 14-18 and 22-30 display sequential NH-NH and C beta H-NH connectivities, indicating that these regions of the peptide adopt nonrandom conformations by significantly populating the alpha-region of conformational space. However, no medium-range dipolar connectivities indicative of nascent helix or turn conformations were observed. At 3 degrees C, almost all residues significantly populate the alpha-region of conformational space, and the nascent helix between residues 3 and 11, with its hydrophobic core, is retained.(ABSTRACT TRUNCATED AT 250 WORDS)

A proton nuclear magnetic resonance study of the mobile regions of human erythroid spectrin

The effect of added NaCl (0-150 mM) and temperature (6-65 degrees C) on the conformation of erythrocyte spectrin was investigated using 400 MHz 1H NMR. The relatively narrow resonances (20-40 Hz linewidth) in the spectra arising from protons in regions of the molecule undergoing rapid motions were selectively detected using either the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence without water presaturation or a simple pi/2 pulse sequence with water presaturation. The T2 relaxation of these protons was not influenced by changes in solution conditions (0-150 mM NaCl, 6-37 degrees C) indicating that their motions were independent of the overall shape of the molecule. Significant increases in the areas of the aliphatic peaks for spectrin samples at fixed salt concentrations occurred as the temperature was raised from 6 to 37 degrees C. The increases were independent of the state of polymerization of spectrin and were greater in the absence of added salt above 25 degrees C. The changes reflect increasing numbers of mobile residues, probably due to partial unfolding of spectrin's repeated structural unit. At temperatures above 37 degrees C, sharp increases in the areas of the spectral envelopes reflect cooperative unfolding of spectrin. Comparison with results previously obtained in this laboratory using CD and ORD indicate that at least part of the lost structure is alpha-helical.

Separation and characterization of two Mg(2+)-ATPase activities from the human erythrocyte membrane

Two distinct Mg(2+)-ATPase activities were isolated from Triton X-100-solubilized human erythrocyte membranes using a combination of calmodulin-agarose to remove Ca(2+)-ATPase and ion exchange chromatography to separate the Mg(2+)-ATPase activities. The activity designated Mg(2+)-ATPase A was inhibited by low concentrations of vanadate (IC50 approximately 2 microM) and by calcium (IC50 approximately 1.5 mM), La3+ (80% inhibition at 0.5 mM), and F- (IC50 approximately 1 mM). Inhibition by F- increased in the presence of 10 microM AlCl3. The activity appeared to be dependent on the concentration of MgATP. Two millimolar deoxyATP supported nearly full activity and 2 mM GTP supported 40% of the activity compared to that seen with 2 mM ATP. The activity was stimulated twofold by the addition of 1% (w/v) phosphatidylserine. These properties are consistent with a role of this enzyme in the control of red blood cell shape, possibly through association with the ATP-dependent translocation of phosphatidylserine and phosphatidylethanolamine from the outer to the inner leaflet of the bilayer. In contrast, Mg(2+)-ATPase B was slightly stimulated by vanadate and by calcium but was unaffected by LaCl3, and by F- +/- AlCl3. The activity was further stimulated by added magnesium in excess of fixed concentrations of ATP. In addition, at a fixed concentration of 10 mM MgCl2, the activity with increasing ATP was biphasic, with the maximum at 1 mM. GTP 2 mM failed to support activity while 2 mM deoxyATP supported only 30% of activity compared to that seen with 2 mM ATP. The activity was not stimulated by oxidized glutathione or the glutathione conjugate lithocholic acid, suggesting it is not involved in the ATP-dependent transport of such compounds out of the erythrocyte.

Characterization of the Mg(2+)-ATPase activity of the human erythrocyte membrane

The Mg(2+)-dependent ATPase activity of human erythrocyte ghosts undergoes biphasic activation in the presence of ATP (K0.5 approximately 20 microM and 400 microM). Inhibition by vanadate is also biphasic with the most sensitive component (IC50 approximately 100 microM) responsible for the remaining activity. La3+ inhibits approximately 70% of activity (IC50 approximately 25 microM) while Cd2+ can fully inhibit activity (IC50 approximately 60 microM). Partially purified activity was obtained by extracting ghosts with Triton X-100, followed by chromatography over Sepharose CL-2B. Triton distorts the curves for inhibition by vanadate and the activation by ATP. The partially purified activity is inhibited by Ca2+ (IC50 approximately 0.4 mM). These results, together with data from other studies, suggest that the total Mg(2+)-ATPase activity in the membrane represents at least two separate enzymes. Only the activity which is highly sensitive to vanadate appears to be involved in erythrocyte shape change.

Band-3 mediated uptake of beryllofluoride complexes by human erythrocytes

Beryllium forms several multivalent fluoride complexes in aqueous solution; the relative concentration of each is governed by the relative concentrations of the constituent ions and pH. In 9Be NMR spectra the 9Be (spin = 3/2) and 19F (spin = 1/2) spin coupling gave rise to an overlapping resonance triplet, quartet, and quintet of BeF2, BeF3-, and BeF4(2-), respectively. The low frequency shift of the quartet (0.31 ppm) and the quintet (0.62 ppm) from the triplet correlated with an increase in the number of 19F-ions in each complex. 19F NMR spectra of the complexes showed that the spin-coupled quartet of each complex was progressively shifted to higher frequency with an increase in the number of F- ions in the complex. Using 9Be and 19F NMR, the multiple equilibrium mixture of complexes was found to shift substantially to favor the BeF3- and BeF4(2-) with a relative increase of NaF concentration. The association constants for BeF2, BeF3-, and BeF4(2-) at 25 degrees C were determined directly from the peak intensities of the spectra, and by a numerical fitting procedure for multiple spectra, and were 0.51 +/- 0.17 mM-2, 0.26 +/- 0.03 mM-1, and 1.0 x 10(-2) +/- 0.1 x 10(-2) mM-1, respectively. 19F NMR spectra of human erythrocytes to which Be2+ and F- were added showed separate resonances from the intracellular populations of the complexes and these were shifted to higher frequency from their extracellular counterparts.(ABSTRACT TRUNCATED AT 250 WORDS)

The inhibition of ATP-dependent shape change of human erythrocyte ghosts correlates with an inhibition of Mg(2+)-ATPase activity by fluoride and aluminofluoride complexes

The vanadate-sensitive Mg(2+)-dependent ATPase activity of the human erythrocyte ghost is believed to be involved in the shape change events that convert echinocytic ghosts to smoothed forms (biconcave discs and stomatocytes). At physiological salt concentration, pH 7.4, 2 mM ATP, 5 mM Mg2+ and 1 mM EGTA, the Mg(2+)-ATPase activity of ghosts was inhibited strongly by millimolar concentrations of sodium fluoride: I50 = 1.31 +/- 0.23 mM (mean +/- S.D.; n = 12). The addition of aluminium chloride to 15 microM reduced the concentration of NaF required for 50% inhibition to 0.76 +/- 0.21 mM (n = 10). Aluminium alone had only a small inhibitory effect on the ATPase activity (13 +/- 9%; n = 10). Desferrioxamine, a strong chelator of tervalent aluminium ion, failed to reverse the inhibition by fluoride and reversed the inhibition in the presence of aluminium and fluoride back to those values obtained with fluoride alone. Of several metal salts tested only beryllium sulfate was able to replace aluminium as an effective inhibitor in the presence of fluoride. Inhibition of the Mg(2+)-ATPase activity by fluoride and the aluminofluoride complexes correlated with an inhibition of the rate of MgATP-dependent change in red cell ghost shape from echinocytes to smoothed forms. All gross morphological changes of the smoothing process were affected, including the production of discocytes, stomatocytes and endocyctic vesicles.

Ectopic pregnancy--a new surgical epidemic

Between March 1972 and September 1981, 154 patients with the diagnosis of ectopic pregnancy were treated at the University of Arizona. A retrospective review of these cases was performed to determine etiologic and demographic factors. Fertility follow-up was obtained in 58 women. Findings are discussed along with the presentation of various thoughts in an attempt to explain this proliferation of a surgical disease.

Caffeine and the fetus: is trouble brewing?

The developing fetus is often subjected to the influence of various drugs ingested by the mother during gestation. Currently, caffeine is one of the more common drugs used by the pregnant patient. It is important that the patient be made aware that caffeine is a drug and that it may cause potential harm to the fetus. Until more scientific data are available, it is our recommendation that moderate to excessive use of caffeine during pregnancy be curtailed and that mild use be decided on an individual basis.

Portable high-resolution laser monochromator-interferometer with multichannel electronic readout

A high-resolution 0.4-m monochromator is described for use in wavelength diagnosis of tunable pulsed and cw laser sources in the 3000-10000-A region. The f/20 design uses an echelle grating in an over-andunder Ebert configuration with a scanned photodiode array to provide a real-time multichannel display of spectral output. Absolute wavelength may be determined to 0.1 A with the monochromator, and a Fabry- Perot interferometer attachment extends linewidth measurement capability to 0.01 A or better. Spectra are displayed on a storage oscilloscope, and calculation of laser parameters is explained. The instrument measures 70 cm long x 15 cm wide x 20 cm high.