Inhibition of clathrin-coated vesicle acidification by duramycin

Cryo-EM structures of intact V-ATPase from bovine brain

The vacuolar-type H⁺-ATPases (V-ATPase) hydrolyze ATP to pump protons across the plasma or intracellular membrane, secreting acids to the lumen or acidifying intracellular compartments. It has been implicated in tumor metastasis, renal tubular acidosis, and osteoporosis. Here, we report two cryo-EM structures of the intact V-ATPase from bovine brain with all the subunits including the subunit H, which is essential for ATPase activity. Two type-I transmembrane proteins, Ac45 and (pro)renin receptor, along with subunit c", constitute the core of the c-ring. Three different conformations of A/B heterodimers suggest a mechanism for ATP hydrolysis that triggers a rotation of subunits DF, inducing spinning of subunit d with respect to the entire c-ring. Moreover, many lipid molecules have been observed in the Vo domain to mediate the interactions between subunit c, c", (pro)renin receptor, and Ac45. These two structures reveal unique features of mammalian V-ATPase and suggest a mechanism of V1-Vo torque transmission.

Duramycin-induced calcium release in cancer cells

Duramycin, through binding with phosphatidylethanolamine (PE), has shown potential to be an effective antitumour agent. However, its mode of action in relation to tumour cells is not fully understood. PE expression on the surface of a panel of cancer cell lines was analysed using duramycin and subsequent antibody labelling, and then analysed by flow cytometry. Cell viability was also assessed by flow cytometry using annexin V and propidium iodide. Calcium ion (Ca) release by tumour cells in response to duramycin was determined by spectrofluorometry following incubation with Fluo-3, AM. Confocal microscopy was performed on the cancer cell line AsPC-1 to assess real-time cell response to duramycin treatment. Duramycin could detect cell surface PE expression on all 15 cancer cell lines screened, which was shown to be duramycin concentration dependent. However, higher concentrations induced necrotic cell death. Duramycin induced calcium ion (Ca) release from the cancer cell lines also in a concentration-dependent and time-dependent manner. Confocal microscopy showed an influx of propidium iodide into the cells over time and induced morphological changes. Duramycin induces Ca release from cancer cell lines in a time-dependent and concentration-dependent manner.

Crystal structure of the human sterol transporter ABCG5/ABCG8

ATP binding cassette (ABC) transporters play critical roles in maintaining sterol balance in higher eukaryotes. The ABCG5/ABCG8 heterodimer (G5G8) mediates excretion of neutral sterols in liver and intestines. Mutations disrupting G5G8 cause sitosterolaemia, a disorder characterized by sterol accumulation and premature atherosclerosis. Here we use crystallization in lipid bilayers to determine the X-ray structure of human G5G8 in a nucleotide-free state at 3.9 Å resolution, generating the first atomic model of an ABC sterol transporter. The structure reveals a new transmembrane fold that is present in a large and functionally diverse superfamily of ABC transporters. The transmembrane domains are coupled to the nucleotide-binding sites by networks of interactions that differ between the active and inactive ATPases, reflecting the catalytic asymmetry of the transporter. The G5G8 structure provides a mechanistic framework for understanding sterol transport and the disruptive effects of mutations causing sitosterolaemia.

Structural properties of the proton translocating complex of the clathrin-coated vesicle

The clathrin-coated vesicle proton pump is a representative member of the new class of endomembrane proton ATPases that share an inhibitor profile which distinguishes them from classic F1F0 and E1E2-type proton pumps. The coated vesicle proton pump is a large (530 kDa) heteroligomer composed of eight polypeptides with molecular masses of 116, 70, 58, 40, 38, 34, 33 and 17 kDa. The 200-fold purified enzyme catalyses ATP-generated proton pumping when reconstituted in liposomes composed of pure lipids. Subunit function has been determined by partial reaction analysis of subunit and subcomplex activities. The isolated 17 kDa subunit, when co-reconstituted with bacteriorhodopsin, forms a dicyclohexylcarbodiimide-inhibitable proton channel. Selective removal of the 116 kDa subunit transforms the proton ATPase from a Mg2+-activatable to a Ca2+-activatable ATPase. Subsequent dissociation and reconstitution of subunits reveals that the 70, 58, 40 and 33 kDa components are required, in composite, to form a functional ATP-hydrolytic core, and that no single subunit or subcomplex deficient in these subunits can catalyse ATP hydrolysis.

Salicylihalamide A inhibits the V0 sector of the V-ATPase through a mechanism distinct from bafilomycin A1

The newly identified specific V-ATPase inhibitor, salicylihalamide A, is distinct from any previously identified V-ATPase inhibitors in that it inhibits only mammalian V-ATPases, but not those from yeast or other fungi (Boyd, M. R., Farina, C., Belfiore, P., Gagliardi, S., Kim, J. W., Hayakawa, Y., Beutler, J. A., McKee, T. C., Bowman, B. J., and Bowman, E. J. (2001) J. Pharmacol. Exp. Ther. 297, 114-120). In addition, salicylihalamide A does not compete with concanamycin or bafilomycin for binding to V-ATPase, indicating that it has a different binding site from those classic V-ATPase inhibitors (Huss, M., Ingenhorst, G., Konig, S., Gassel, M., Drose, S., Zeeck, A., Altendorf, K., and Wieczorek, H. (2002) J. Biol. Chem. 277, 40544-40548). By using purified bovine brain V-pump and its dissociated V(1) and V(0) sectors, we identified the recognition and binding site for salicylihalamide to be within the V(0) domain. Salicylihalamide does not inhibit the ATP hydrolysis activity of the dissociated V(1)-ATPase but inhibits the ATPase activity of the holoenzyme by inhibiting the V(0) domain. Salicylihalamide causes a dramatic redistribution of cytosolic V(1) from soluble to membrane-associated form, a change not observed in cells treated with either bafilomycin or NH(4)Cl. By synthesizing and characterizing a series of salicylihalamide derivatives, we investigated the structural determinants of salicylihalamide inhibition in terms of potency and reversibility, and used this information to suggest a possible binding mechanism.

Characterization of the functional coupling of bovine brain vacuolar-type H(+)-translocating ATPase. Effect of divalent cations, phospholipids, and subunit H (SFD)

Vacuolar-type H+-translocating ATPases (V-ATPases or V-pumps) are complex proteins containing multiple subunits and are organized into two functional domains: a peripheral catalytic sector V1 and a membranous proton channel V0. The functional coupling of ATP hydrolysis activity to proton transport in V-pumps requires a regulatory component known as subunit H (SFD) as has been shown both in vivo and in vitro (Ho, M. N., Hirata, R., Umemoto, N., Ohya, Y., Takatsuki, A., Stevens, T. H., and Anraku, Y. (1993) J. Biol. Chem. 268, 18286-18292; Xie, X. S., Crider, B. P., Ma, Y. M., and Stone, D. K. (1994) J. Biol. Chem. 269, 25809-25815). Ca2+ is thought to uncouple V-pumps because it is found to support ATP hydrolysis but not proton transport, while Mg2+ supports both activities. The direct effect of phospholipids on the coupling of V-ATPases has not been reported, likely due to the fact that phospholipids are constituents of biological membranes. We now report that Ca2+-induced uncoupling of the bovine brain V-ATPase can be reversed by imposition of a favorable membrane potential. Furthermore we report a simple "membrane-free" assay system using the V0 proton channel-specific inhibitor bafilomycin as a probe to detect the coupling of V-ATPase under certain conditions. With this system, we have characterized the functional effect of subunit H, divalent cations, and phospholipids on bovine brain V-ATPase and have found that each of these three factors plays a critical role in the functional coupling of the V-pump.

The interaction of tributyllead with lysosomes from rat liver

The interactions of tributyllead with lysosomes from rat liver have been studied. It results that the organometal compound induces a fast alkalinization in energized lysosomes. The interpretation is that the compound is a potent proton carrier. This function could explain the toxicity, in particular at neurological level of the compound.

The interactions of trialkyltin compounds with lysosomes from rat liver

Interactions of two trialkyltin compounds with the lysosomes from a rat liver have been studied. It is shown that these compounds induce a fast alkalinisation in the matrix of energised lysosomes. The fast alkalinisation rate is similar to the one obtained with uncouplers of the oxidative phosphorylation. An identical effect has been obtained with lysosomes energised in a chloride-free medium. This supports the hypothesis that trialkyltin compounds behave not only as Cl-/OH- exchangers, but also as proton carriers in biological membranes. This result could explain the toxicity and in particular the neurotoxicity of trialkyltin compounds.

Recombinant SFD isoforms activate vacuolar proton pumps

The vacuolar proton pump of clathrin-coated vesicles is composed of two general sectors, a cytosolic, ATP hydrolytic domain (V1) and an intramembranous proton channel, V0. V1 is comprised of 8-9 subunits including polypeptides of 50 and 57 kDa, termed SFD (Sub Fifty-eight-kDa Doublet). Although SFD is essential to the activation of ATPase and proton pumping activities catalyzed by holoenzyme, its constituent polypeptides have not been separated to determine their respective roles in ATPase functions. Recent molecular characterization of these subunits revealed that they are isoforms that arise through an alternative splicing mechanism (Zhou, Z., Peng, S.-B., Crider, B.P., Slaughter, C., Xie, X.S., and Stone, D.K. (1998) J. Biol. Chem. 273, 5878-5884). To determine the functional characteristics of the 57-kDa (SFDalpha)1 and 50-kDa (SFDbeta) isoforms, we expressed these proteins in Escherichia coli. We determined that purified recombinant proteins, rSFDalpha and rSFDbeta, when reassembled with SFD-depleted holoenzyme, are functionally interchangeable in restoration of ATPase and proton pumping activities. In addition, we determined that the V-pump of chromaffin granules has only the SFDalpha isoform in its native state and that rSFDalpha and rSFDbeta are equally effective in restoring ATPase and proton pumping activities to SFD-depleted enzyme. Finally, we found that SFDalpha and SFDbeta structurally interact not only with V1, but also withV0, indicating that these activator subunits may play both structural and functional roles in coupling ATP hydrolysis to proton flow.

Synapsins I and II are ATP-binding proteins with differential Ca2+ regulation

Synapsins I and II are abundant phosphoproteins that are localized to synaptic vesicles and have essential functions in regulating synaptic vesicle exocytosis. Synapsins contain a single evolutionarily conserved, large central domain, the C-domain, that accounts for the majority of their sequences. Unexpectedly, the crystal structure of the C-domain from synapsin I revealed that it is structurally closely related to several ATPases despite the absence of sequence similarities (Esser, L., Wang, C.-R., Hosaka, M., Smagula, C. S., Südhof, T. C., and Deisenhofer, J. (1998) EMBO J., in press). We now show that the C-domains of both synapsin I and synapsin II constitute high affinity ATP-binding modules. The two C-domains exhibit similar ATP affinities but are differentially regulated; ATP binding to synapsin I is Ca(2+)-dependent whereas ATP binding to synapsin II is Ca(2+)-independent. In synapsin I, the Ca2+ requirement for ATP binding is mediated by a single, evolutionarily conserved glutamate residue (Glu373) at a position where synapsin II contains a lysine residue. Exchange of Glu373 for lysine converts synapsin I from a Ca(2+)-dependent protein into a Ca(2+)-independent ATP-binding protein. Our studies suggest that synapsins I and II function on synaptic vesicles as ATP-binding proteins that are differentially regulated by Ca2+.

Subunit G of the vacuolar proton pump. Molecular characterization and functional expression

The vacuolar type proton pump of clathrin-coated vesicles has a multisubunit ATP hydrolytic center that is peripheral to the membrane. Polypeptides present in this domain include the well characterized subunits A, B, C, D, E, and F; SFD, a dimer composed of 50- and 57-kDa polypeptides; and polypeptides termed G and H. Of these, subunits A, B, C, and E have been shown to be necessary but not sufficient for significant ATPase activity; in addition, either polypeptide G or H is also required for ATP hydrolysis (Xie, X.-S. (1996) J. Biol. Chem. 271, 30980-30985). In this study, the polypeptides G and H were purified and directly sequenced. Subsequent molecular analysis has revealed that these proteins are isoforms, which we designate G1 and G2. The cDNAs encoding the rat and bovine brain and chicken osteoclast forms of G1 have been cloned. The open reading frames of the rat and bovine clones encode hydrophilic proteins of 118 amino acids that differ at only five residues; bovine G1 has 36% identity with VMA10, a component of the proton channel of yeast. Northern blot analysis revealed a 1. 0-kilobase pair transcript encoding G1 in bovine brain, kidney, heart, and spleen. The cDNA encoding bovine polypeptide H was cloned and sequenced, revealing this protein to be 64% identical to G1, constituting isoform G2. In Northern blot analysis, a single 1. 7-kilobase pair transcript hybridized with a probe to G2 in brain, but not in heart, kidney, or spleen. An antibody against a bovine G1-specific domain reacts with V pump from bovine brain, kidney, and chromaffin granule, whereas an anti-G2 antibody reacts only with proton pump from brain. The bovine forms of G1 and G2 were subsequently expressed in Escherichia coli and Sf9 cells, respectively, and purified to homogeneity. Reconstitution of ATP hydrolysis was achieved by combination of recombinant subunits A, B, C, and E with either recombinant G1 or G2, demonstrating the role of these isoforms in pump function.

Biochemical characterization of a V-ATPase of tracheal smooth muscle plasma membrane fraction

A biochemical characterization of a Mg(2+)-ATPase activity associated with a plasma membrane fraction isolated from airway (tracheal) smooth muscle was performed. This enzyme is an integral part of the membrane remaining tightly bound after 0.6 M KCl extraction. This enzyme activity showed a cold inactivation in the presence of ATP and Mg2+. Also, this Mg(2+)-ATPase was stimulated by monovalent anions being Cl-, the best anion for such stimulation, even though Br- and I- were good substitutes and F- was ineffective. This Cl--stimulated activity showed a powerful nucleosidetriphosphatase activity having the following divalent cation specificity: Mg2+ > Mn2+ > Ca2+, where Zn2+ and Fe2+ were ineffective. This ATPase activity was not inhibited by ouabain oligomycin C and vanadate indicating that neither P- or F-ATPases were associated with this enzyme activity. However, the existence of a V-ATPase was shown by the significant inhibition causes by bafilomycin A1. Additionally, this V-ATPase seems to be coupled to Cl- conductor because duramycin inhibited this ATPase activity. The presence of a H+ pump associated to this V-ATPase was shown indirectly, through the stimulatory effect produced by uncouplers such as FCCP and 1799, which were able to produce significant stimulation of this V-ATPase indicating the existence of a H(+)-ATPase. Finally, the immunodetection of a 72 kDa polypeptide using a specific antibody against the A subunit (72 kDa) of V-ATPase from chromaffin granule demonstrated the presence of a V-ATPase in this plasma membrane fraction.

Biosynthesis and biological activities of lantibiotics with unique post-translational modifications

Lantibiotics are biologically active peptides which contain the thioether amino acid lanthionine as well as several other modified amino acids. They can be broadly divided into two groups on the basis of their structures: type-A lantibiotics are elongated, amphiphilic peptides, while type-B lantibiotics are compact and globular. In the last decade there has been a marked increase in research interest in these peptides due both to the novel biosynthetic mechanisms by which they are produced, as well as to their potential applications. Lantibiotics are synthesised on the ribosome as a prepeptide which undergoes several post-translational modification events, including dehydration of specific hydroxyl amino acids to form dehydroamino acids, addition of neighbouring sulfhydryl groups to form thioethers and, in specific cases, other modifications such as introduction of D-alanine residues from L-serine, formation of lysinoalanine bridges, formation of novel N-terminal blocking groups and oxidative decarboxylation of a C-terminal cysteine. The genetic elements responsible for these specific modification reactions encode unique enzymes with hitherto unknown reaction mechanisms. Production of these peptides also requires accessory proteins including processing proteases, translocators of the ATP-binding cassette transporter family, regulatory proteins and dedicated producer self-protection mechanisms. While the principle biological activity of most type-B lantibiotics appears to be directed at the inhibition of enzyme functions, the type-A lantibiotics kill bacterial cells by forming pores in the cytoplasmic membrane.

Iron binding, a new function for the reticulocyte endosome H(+)-ATPase

The significance of the H(+)-ATPase in iron absorption by rabbit reticulocytes is explored using isolated endosomes, effects of inhibitors, and the purified proton pump. We have recently reported H(+)-ATPase-mediated iron transfer across a liposomal membrane (Li et al., 1994). In this report, the effect of H(+)-ATPase inhibitors on iron mobilization is investigated at pH 6.0 in the presence of 15 microM FCCP in order to dissociate 59Fe(III) from transferrin and eliminate the kinetic effects of acidification by the ATPase. Iron transport by isolated endosomes is decreased 50% by the cation pore inhibitor dicyclohexylcarbodiimide (DCCD) for ascorbate-mediated iron mobilization and increased by 40-50% when NADH and ferrocyanide are used as electron donors. In contrast, the ATPase hydrolysis inhibitors N-methylmaleimide (NEM) and 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD) increase iron mobilization when NADH and ferrocyanide are used as reductants but have negligible effects for ascorbate. The differential inhibition or enhancement by DCCD, NEM, and NBD with respect to the reductants used for mobilization indicates that the H(+)-ATPase may be involved in the multiple pathways or iron transport found in isolated rabbit reticulocyte endosomes. Effects of inhibitors of ATP hydrolysis suggest significant structural interactions between the proton pump and sites for iron binding and/or reduction. The isolated H(+)-ATPase binds iron as revealed by using nondenaturing electrophoretic and chromatographic methods. One class of iron binding sites is suggested to be the 17.5 kDa proton pore subunits of the H(+)-ATPase which also covalently react with DCCD.(ABSTRACT TRUNCATED AT 250 WORDS)

Duramycin increases intracellular calcium in airway epithelium

Duramycin increases short-circuit current (Isc) and net Cl- secretion in tracheal epithelium. We measured the intracellular free calcium ([Ca2+]i) response to duramycin using Indo-1 and bovine and canine tracheal cell suspensions, and the effect of an intracellular calcium chelator, BAPTA, and the protein kinase C inhibitor, staurosporine, on the Isc and [Ca2+]i response to duramycin. [Ca2+]i increased in a dose-dependent manner from basal levels of 34 +/- 5 to 949 +/- 136 nM at 5 x 10(-6) M duramycin. Both BAPTA (50 microM) and staurosporine (5-50 nM) pretreatment blunted the increase in Isc and net Cl- secretion produced by duramycin. BAPTA also blunted the rise in [Ca2+]i produced by duramycin (5 x 10(-6) M) in the presence of extracellular calcium (499 +/- 122 nM). In the absence of extracellular calcium, the duramycin-induced (5 x 10(-6) M) rise in [Ca2+]i was blunted from 949 +/- 136 nM (stimulation in the presence of Ca2+) to 621 +/- 122 nM, and was further decreased in the presence of BAPTA to 197 +/- 42 nM. In contrast, staurosporine (50 nM) pretreatment had no effect on the rise in [Ca2+]i produced by duramycin (basal 90 +/- 27 to 861 +/- 110 nM at 5 x 10(-6) M). Duramycin had no effect on [Ca2+]i in human neutrophils. These data demonstrate that duramycin releases calcium from intracellular stores and stimulates the influx of calcium in airway epithelial cells. These data also demonstrate that, in the presence of protein kinase C pathway blockade, an increase in intracellular free calcium is not sufficient for chloride secretion; thus, duramycin-stimulated chloride secretion may depend upon protein kinase C.

Structure and properties of the coated vesicle (H+)-ATPase

Clathrin-coated vesicles play an important role in both receptor-mediated endocytosis and intracellular membrane traffic in eukaryotic cells. The coated vesicle (H+)-ATPase functions to provide the acidic environment within endosomes and other intracellular compartments necessary for receptor recycling and intracellular membrane traffic. The coated vesicle (H+)-ATPase is composed of nine different subunits which are divided into two distinct domains. The peripheral V1 domain, which has the structure 73(3):58(3):40(1):34(1):33(1), possesses the nucleotide binding sites of the (H+)-ATPase. The integral V0 domain, which has the composition 100(1):38(1):19(1):17(6), contains the pathway for proton conduction across the membrane. Topographical analysis indicates a structure for the coated vesicle (H+)-ATPase very similar to that of the F-type ATPases. Reassembly studies have allowed us to probe the function of particular subunits in this complex and the activity properties of the separate domains. These studies have led to insights into possible mechanisms of regulating vacuolar acidification.

Ion channel formation by duramycin

The formation of ion channels by the nonadecapeptide antibiotic duramycin was examined using black lipid membranes and using the patch-clamp technique. In black lipid membranes made from glyceryl monooleate or a phosphatidylcholine/phosphatidylethanolamine mixture, duramycin induced complex fluctuations in membrane conductance, some step-like and some which were incapable of being resolved into discrete conductance states. Both conductance and largest step size increased with time. A similar time-dependent increase in conductance was seen in patch-clamp experiments with HCA-7 Colony 29 human colonic epithelial cell. The channels displayed weak anion selectivity and the smaller channels formed in patches from epithelial cells showed weak inward-rectification. Channel formation by duramycin was achieved at lower concentrations when the black lipid membrane was made with phospholipid rather than with glyceryl monooleate. Lower concentrations were effective in generating conductances in epithelial cells than in bilayers. It is concluded that duramycin forms ion channels in both artificial and biological membranes. Accumulation of duramycin and coalescence of initially small channels into larger ones is considered to be responsible for the recorded behaviour and to final disruption of membranes.

Increased number and microtubule-associated dispersal of acidic intracellular compartments accompany differentiation of cultured human keratinocytes

Intracellular acidic compartments serve several functions, including uptake of nutrients, processing and sorting of secreted and membrane-bound proteins, and even entry of viruses into cells. In this study, we examined the distribution of acidic compartments in normal human keratinocytes cultured in serum-free medium. Acridine orange was used to stain acidic organelles (red fluorescence), and adherent cells were evaluated by fluorescence microscopy and by interactive laser cytometry (ILC). Keratinocytes cultured in low [Ca++] (0.15 mM) exhibited morphologic characteristics associated with basal cells; red acidic vesicles in these cells were aggregated around the nucleus, sparing the peripheral cytoplasm. After 24 h of culture in high [Ca++] (1.5 mM) keratinocytes showed morphologic changes associated with differentiated cells, including increased number and dispersal of red vesicles to the periphery of the cytoplasm. Keratinocytes cultured in 0.15 mM [Ca++], but treated with phorbol 12-myristate 13-acetate (PMA, 5-100 ng/ml) to induce terminal differentiation, developed similar features. Incubation in media with either high [Ca++] or PMA also induced radial extension of the microtubule network, suggesting that the distribution of acidic organelles occurs along this network. Finally, crude keratinocyte membranes were evaluated by radioactive assay for the presence of three ion-translocating ATPase activities, plasma membrane Na/K ATPase, mitochondrial ATPase, and vacuolar H+ pump ATPase, the latter being the activity responsible for acidification of intracellular compartments. Both basaloid and differentiated keratinocytes exhibited similar vacuolar H+ pump ATPase activity, as measured by its sensitivity to bafilomycin.

Duramycin effects on the structure and function of heart mitochondria. II. Energy conversion reactions

The polypeptide antibiotic duramycin has been reported to interact selectively with phosphatidylethanolamine (PE) and monogalactosyldiacylglycerol (Navarro et al., 1985, Biochemistry 24, 4645-4650). PE is a major component of mitochondrial membranes. Duramycin was used to probe the role of PE in mitochondrial energy conversion reactions with the following results: (i) Duramycin uncoupled mitochondrial respiration, decreasing the respiratory control ratio to 1 at 5 microM. At concentrations of duramycin in excess of 10 microM, ADP addition inhibited electron transport. (ii) Duramycin inhibited oxidative phosphorylation (C50 less than 2 microM). (iii) Duramycin stimulated mitochondrial ATP hydrolysis modestly. The antibiotic was 7- to 16-fold less effective in this regard than concentrations of carbonylcyanide p-trifluoromethoxyphenylhydrazone (F-CCP) which produced comparable uncoupling. (iv) Duramycin inhibited uncoupled ATPase activity (C50 = 8 microM). Inhibition of the ATPase activity of intact mitochondria was blocked by 1 mM MgCl2 and 5 mM CaCl2; inhibition persisted in sub-mitochondrial particles assayed in the presence of 3 mM MgCl2. The effects on mitochondrial function of free fatty acids (FFA) and duramycin are similar in many respects. It is suggested that duramycin, like FFA, uncouples via a nonclassical mechanism, possibly by disrupting intramembrane H+ transfer between redox and ATPase complexes. In addition, interaction of duramycin, either direct or indirect, with the F0 moiety of the mitochondrial ATPase and with one or more components of the respiratory electron transport chain is proposed.

Vacuolar acidification and bafilomycin-sensitive proton translocating ATPase in human epidermal Langerhans cells

Langerhans cells (LC) are the principal antigen-presenting cells (APC) of squamous epithelia. We have previously shown that freshly isolated LC (fLC) are able to deliver endocytosed membrane MHC class II molecules into acidic environments, and that this capacity is lost when LC are placed in culture (cLC). Inasmuch as processing of antigens requires their passage through acidic compartments, we undertook the present study to examine the ability of fLC and cLC to take up acridine orange, and to identify proton-translocating ATPases in these cells. Using flow cytometry and fluorescence microscopy, acridine orange was observed to accumulate in acidic compartments in both fLC and cLC. Using a radioactive ATPase assay, crude membrane preparations from both fLC and cLC were shown to possess three types of ion-translocating ATPase, based on sensitivity to the following inhibitors: ouabain (Na+, K+ ATPase), oligomycin (mitochondrial F1F0 ATPase), and bafilomycin (vacuolar-type proton pump ATPase); the last type is responsible for acidification in vacuolar compartments. cLC displayed markedly less (less than 50%) total ATPase activity compared to fLC; however, the relative proportions of specific ATPases were similar in fLC and cLC. Combined use of the three inhibitors resulted in abrogation of only 25-40% of the total ATPase activity. Finally, treatment of LC with bafilomycin inhibited both acridine orange uptake and acidification of internalized HLA-DR molecules. These results confirm the ability of both fLC and cLC to acidify vacuolar compartments, thereby suggesting that lack of acidification of endocytosed membrane class II molecules in cultured cells is due to alternative routing to non-acidic organelles.

Two types of clathrin-coated vesicles isolated from rat brain: analysis of biochemical properties and cellular origin

Two major fractions rich in clathrin-coated vesicles (CVs) (fraction I, rho = 1.140 g/cm3; fraction II, rho = 1.113 g/cm3) were separated from rat brain using a sucrose gradient and compared for their cellular origins and Cl- translocation systems. Electron micrographs showed that both fractions contained CVs of different size distributions (fraction I, 85 +/- 9.5 nm in diameter; fraction II, 72 +/- 6.8 nm in diameter). Fraction II contained potent ouabain-sensitive ATPase activity, whereas fraction I contained only a little activity. Immunoblot analysis for the Na+,K(+)-ATPase catalytic subunit, alpha and alpha(+), demonstrated that fraction II exhibited predominantly alpha(+), whose proportion to alpha was analogous to that observed in the extracts of primary cultured neuronal cells. Furthermore, on a sucrose density gradient, cultured neuronal cells yielded fraction II but not fraction I, whereas primary cultured glial cells yielded fraction I but not fraction II. Labeling-chase experiments using 125I-transferrin in cultured neuronal cells showed the internalized ligand in fraction II and the surface-bound ligand in the fraction with lower density (rho = 1.090 g/cm3), a result suggesting that the involvement of Na+,K(+)-ATPase in fraction II is attributable to endocytic vesicles. Cl- uptake in fraction II was approximately threefold higher than that in fraction I. N-Ethylmaleimide (100 microM) completely inhibited the Cl- uptake in fraction I but partially (approximately 50%) inhibited that in fraction II. These findings suggest that the two CV fractions isolated from rat brain originate from different cell types--glial and neuronal cells--and differ in size distribution of CVs, content of Na+,K(+)-ATPase, and mechanism for Cl- uptake.

Characterization of a tartrate-resistant acid phosphatase (ATPase) from rat bone: hydrodynamic properties and N-terminal amino acid sequence

Certain physicochemical properties of rat bone tartrate-resistant acid ATPase (TrATPase), including the size and shape of the enzyme, potential subunit composition, and detergent binding, have been elucidated. SDS-polyacrylamide gel electrophoresis in combination with immunoblot analysis showed that the bone TrATPase has a molecular weight of 33,000 D and is composed of disulfide-linked polypeptides of 20,000 and 16,000 D. The enzyme contains 1.7 mol Fe per mol enzyme. Hydrodynamic studies allowed calculation of the Stokes radius (24 A), the sedimentation coefficient (3.19S), the partial specific volume (0.748 ml/g), the frictional ratio (0.995), and the axial ratio (1.0). The amount of detergent bound to the protein was determined to 4 mol of Triton X-100 per mol enzyme. The molecular weight of bone TrATPase derived from these parameters was 31,900 D. N-terminal amino acid sequence analysis of the Mr 20,000 subunit indicated a high degree of similarity with TRAP enzymes from spleen, uterus, placenta, hairy cell leukemia, and osteoclastoma. It is concluded that rat bone TrATPase belongs to the type 5 (tartrate-resistant and purple) acid phosphatase family. The similarities in the N-terminal amino acid sequences, iron content, and physicochemical properties of TRAP enzymes indicate a close structural relationship between type 5 acid phosphatases expressed in different tissues. The findings that TrATPase has a spherical shape and binds low amounts of detergent suggest that the enzyme is a soluble protein, compatible with the view that TrATPase is secreted by the osteoclast.

Duramycin enhances chloride secretion in airway epithelium

The effect of duramycin, a polypeptide antibiotic, on Cl- transport in canine tracheal epithelium mounted in Ussing chambers was studied. Over a narrow concentration range, duramycin increased short-circuit current (Isc) and net Cl- secretion and had no effect on mannitol flux when added to the mucosal bathing solution. The maximum increase in Isc was observed at a duramycin concentration of 2 X 10(-6) M and was associated with an increase in both unidirectional Cl- fluxes. Higher duramycin concentrations produced a decrease in Isc. Submucosal addition of duramycin had no effect on Isc except at high concentrations. Pretreatment of tissues with mucosal amiloride (10(-4) M) to reduce basal Na+ transport had no effect on the subsequent response to duamycin. In other tissues pretreated with 10(-3) M dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP), duramycin produced a further increase in Isc and net Cl- secretion similar to its effect in nonpretreated tissues. In all instances the increase in Isc was entirely accounted for by an increase in net Cl- secretion. We conclude that duramycin increases Isc and Cl- secretion in airway epithelium. Although the mechanism of activation is not known, these data demonstrate that duramycin increases Cl- secretion by a pathway other than cAMP. An understanding of the mechanism of action of duramycin may further our understanding of Cl- secretion regulation in airway epithelium.

Chloride ion increases [3H]dopamine accumulation by synaptic vesicles purified from rat striatum: inhibition by thiocyanate ion

The effect of chloride ion on the transport of [3H]dopamine into synaptic vesicles purified from rat striatum has been evaluated. The inclusion of 10 mM chloride ion in the incubation medium produced a 100% increase in temperature-sensitive [3H]dopamine uptake into synaptic vesicles from approximately 1800 pmol/mg to 3600 pmol/mg of protein. Half-maximal effects were observed with chloride ion at 4 mM concentration. The anion selectivity of stimulation supports the presence of anion channels within the membranes of dopaminergic storage organelles. Low concentrations of thiocyanate ion (less than 10 mM), 4-acetamido-4'-isothiocyano-2-2'-disulfonic acid stilbene (100 microM), and duramycin (5 micrograms/ml) selectively blocked the chloride ion stimulated accumulation of [3H]dopamine. Higher concentrations of these agents are required to significantly reduce [3H]dopamine uptake in the absence of chloride ion. These results suggest that both components of the proton electrochemical gradient (delta psi and delta pH) are important for dopamine uptake by brain vesicles. This article presents the first demonstration that chloride ion plays a role in the transport of dopamine into vesicles isolated from the CNS.

Vacuolar proton pumps

Recently a new class of proton-translocating ATPases has been localized to endomembrane compartments in plant, fungal, and mammalian cells. These proton pumps are large hetero-oligomers which have an ATP hydrolytic sector that is functionally and structurally distinct from a transmembranous proton pore. Enzymatic characteristics of these proton pumps are discussed as well as the current state of knowledge regarding subunit composition and function. In addition, recent primary sequence data are discussed which indicate that these proton pumps share a common ancestor with F1F0-type proton pumps of mitochondria.

Duramycin effects on the structure and function of heart mitochondria. I. Structural alterations and changes in membrane permeability

The polypeptide antibiotic duramycin has been reported to interact specifically with two lipids: phosphatidylethanolamine (PE) and monogalactosyldiacylglycerol (Navarro et al. (1985) Biochemistry 24, 4645-4650). PE is a major component of mitochondrial membranes. Duramycin was used to examine the role of PE in maintenance of mitochondrial structure and membrane permeability properties with the following results: (1) Duramycin addition to isolated rat heart mitochondria produced abrupt organelle contraction which was followed, depending on composition of the suspending medium, by pronounced swelling. The most notable morphological effect of the antibiotic was ruffling or crenelation of the outer membrane, which resulted ultimately in its separation from the inner membrane. (2) Low concentrations (less than 5 microM) of the antibiotic selectively increased the permeability of the mitochondrial inner membrane to cations and small solutes. This effect was blocked by atractyloside, a highly specific inhibitor of the adenine nucleotide translocator, by palmitoyl coenzyme A, by N-ethylmaleimide, and by AMP, ADP and ATP but not GDP or GTP, implicating the adenine nucleotide translocator in the selective permeability increase. (3) Higher concentrations of duramycin induced a more generalized permeability increase which was not subject to inhibition by compounds capable of interacting with the adenine nucleotide translocator.

Mutation of Bacillus firmus OF4 to duramycin resistance results in substantial replacement of membrane lipid phosphatidylethanolamine by its plasmalogen form

Mutant strains of alkalophilic Bacillus firmus OF4 that were selected for resistance to duramycin had greatly reduced levels of membrane diacylphosphatidylethanolamine, as had been found in studies of such mutants of Bacillus subtilis. In the B. firmus strains, however, substantial levels of plasmenylethanolamine were found. This is an unusual membrane component for an aerobic eubacterium, but the presence of trace amounts even in the wild type was confirmed in experiments with 32Pi-labeled growth medium. The membrane lipid composition of the duramycin-resistant strains had several other changes that also left alkalophilic growth unimpaired.

Large decreases in membrane phosphatidylethanolamine and diphosphatidylglycerol upon mutation to duramycin resistance do not change the protonophore resistance of Bacillus subtilis

Duramycin-resistant mutant strains were selected from wild-type Bacillus subtilis (BD99) and its protonophore-resistant mutant derivative, strain AG1A3. Analyses of the membranes of the duramycin-resistant mutants showed that they had little or no phosphatidylethanolamine and diphosphatidylglycerol as determined by chemical detection after thin-layer chromatography. Small amounts of these phospholipids must remain in the mutant strains, however, because during studies of incorporation of exogenous, radioactive fatty acids, label associated with palmitoleic acid was found in chromatographic positions that corresponded to the expected positions of phosphatidylethanolamine and diphosphatidylglycerol. The duramycin-resistant strains both showed elevated levels of phosphatidylglycerol and aminoacyl(lysyl)phosphatidylglycerol. The duramycin-resistant derivative of protonophore-resistant AG1A3 (AG1A3-DR4), but not that of the wild type, also showed a decreased content of neutral relative to polar lipid in the membrane. The composition of neutral lipid in that strain was higher in free fatty acids and lower in 1,2-diacylglycerol than its parent strain. AG1A3-DR4 also contained appreciable levels of lysophosphatidylethanolamine and somewhat elevated diglycosyldiacylglycerol relative to the other strains in the study. The protonophore resistance of AG1A3 was unaltered by mutation to duramycin resistance. Nor was there any change in the efficacy of exogenous palmitoleic acid in diminishing the protonophore resistance of AG1A3-DR4. This phenomenon persists upon dramatic reduction in the content of phosphatidylethanolamine and diphosphatidylglycerol even though those phospholipids are normally the preferred sites of incorporation of the exogenous unsaturated fatty acids that mediate the effect.

Interaction of a cyclic peptide, Ro09-0198, with phosphatidylethanolamine in liposomal membranes

Ro09-0198 is a cyclic peptide isolated from Streptoverticillium griseoverticillatum. This peptide caused permeability increase and aggregation of liposomes containing phosphatidylethanolamine. Liposomes containing phosphatidylserine, phosphatidylinositol or cardiolipin instead of phosphatidylethanolamine were, however, not appreciably reactive with the peptide. Among the structural analogs of phosphatidylethanolamine, dialkylphosphatidylethanolamine and 1-acylglycerophosphoethanolamine incorporated into liposomes could interact with Ro09-0198 to cause a permeability increase, whereas liposomes consisting of alkylphosphoethanolamine or phosphatidyl-N-monomethylethanolamine were insensitive to the peptide. These findings indicate that a glycerol backbone and a primary amino group of phosphatidylethanolamine are necessary for interaction with Ro09-0198 to cause membrane damage. Ro09-0198 induced a selective permeability change on liposomes. Glucose and umbelliferyl phosphate were effluxed significantly, but sucrose was only slightly permeable and inulin could not be released. Consequently, the permeability increase induced by Ro09-0198 is rather specific to molecules smaller than sucrose. Line broadening of electron spin resonance signals of spin-labeled phosphatidylethanolamine was observed upon treatment of liposomes with Ro09-0198. It was suggested from these results that Ro09-0198 can alter the physical organization of phosphatidylethanolamine in membranes, thus providing a basis for changes in membrane permeability.

Hemolytic activity of a cyclic peptide Ro09-0198 isolated from Streptoverticillium

Ro09-0198, a cyclic peptide isolated from culture filtrates of Streptoverticillium griseoverticillatum, induced lysis of erythrocytes. Preincubation of the peptide with phosphatidylethanolamine reduced the hemolytic activity, whereas other phospholipids present in erythrocytes in nature had no effect. A study of the structural requirements on phosphatidylethanolamine necessary for interaction with the peptide indicates that Ro09-0198 recognizes strictly a particular chemical structure of phosphatidylethanolamine: dialkylphosphoethanolamine as well as 1-acylglycerophosphoethanolamine showed the same inhibitory effect on hemolysis induced by Ro09-0198 as diacylphosphatidylethanolamine, whereas phosphoethanolamine gave no inhibitory effect. Neither phosphatidyl-N-monomethylethanolamine nor alkylphosphopropanolamine had an inhibitory effect. Consequently, the hydrophobic chain is necessary for the interaction and the phosphoethanolamine moiety is exactly recognized by the peptide. Ro-09-0198-induced hemolysis was temperature-dependent and the sensitivity of hemolysis differed greatly among animal species.

Effects of antibiotics and other inhibitors on ATP-dependent protein translocation into membrane vesicles

The effects of several membrane antibiotics and other agents on ATP-dependent protein translocation were examined in membrane vesicles under conditions where no significant proton motive force was present. The membrane perturbants ethanol and procaine abolished ATP-dependent protein translocation. Phenethyl alcohol at low concentrations abolished translocation, whereas at high concentrations it allowed precursors to be translocated but inhibited their processing. Translocation of precursors promoted by phenethyl alcohol was temperature dependent and occurred without an added energy source but was enhanced by ATP. However, such precursors could not be further processed to mature forms upon removal of the alcohol. The membrane-active antibiotics polymyxin B and gramicidin S were strong inhibitors of translocation, whereas gramicidin D, cerulenin, and mycobacillin had no effect even at higher concentrations, indicating some specificity in interference with protein translocation. Duramycin, an antibiotic previously shown to affect protein-lipid interaction, severely impaired protein translocation. These results showed that membrane structures play important roles, either directly or indirectly, in protein translocation. Chelating agents 1,10-phenanthroline and EDTA, but not EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid], also abolished protein translocation.