Membrane proteins of the vacuolar system. III. Further studies on the composition and recycling of endocytic vacuole membrane in cultured macrophages

In previous publications, we found that the membrane of macrophage phagolysosomes could be selectively radioiodinated in living cells. The technique required phagocytosis of lactoperoxidase covalently coupled to latex spheres (LPO-latex), followed by iodination on ice with Na125I and hydrogen peroxide. In this paper, we use the LPO-latex system to further analyze the composition and recycling of phagocytic vacuole membrane. Three approaches were employed to examine the polypeptide composition of the phagolysosome (PL) and plasma membranes (PM). The efficiency of intracellular iodination was increased by increasing lysosomal pH with chloroquine. By one-dimensional SDS PAGE, the heavily labeled chloroquine-treated PL exhibited the same labeled polypeptides as PM iodinated extracellularly with LPO-latex. Iodinated PL and PM were compared by two-dimensional gel electrophoresis. No differences in the isoelectric point and molecular weight of the major iodinated species were detected. Quantitative immune precipitation was performed with five specific antibodies directed against cell surface antigens. Four antibodies precipitated similar relative amounts of labeled antigen on the cell surface and endocytic vacuole. One antibody, secreted by hybridoma 2.6, detected a 21-kdalton polypeptide that was enriched sevenfold in PL membrane. This enrichment was cell surface-derived, since the amount of labeled 2.6 was increased sevenfold when iodinated PM was driven into the cell during latex uptake. Therefore, intracellular iodination primarily detects PL proteins that are identical to their PM counterparts. Additional studies employed electron microscope autoradiography to monitor the centrifugal flow of radiolabeled polypeptides from PL to PM. Cells were iodinated intralysosomally and returned to culture for only 5-10 min at 37°C. Most of the cell-associated label then redistributed to the cell surface or its adjacent area. Significant movement out of the lysosome compartment occurred even at 2°C and 22°C. Extensive and rapid membrane flow through the secondary lysosome presumably contributes to the great similarity between PM and PL membrane polypeptides

The Membrane Polypeptides of the Vacuolar System: Composition and Recycling

A method has been developed to deliver an iodinating system into the confines of the phagolysosome, allowing us to study the nature of the phagolysosomal membrane. Lactoperoxidase (LPO) is covalently coupled to carboxylated latex spheres (LPO-latex) in a stable enzymatically active form. The addition of LPO-Iatex to cultured macrophages leads to their rapid attachment, ingestion, and enclosure in a plasma membranederived phagocytic vacuole. These organelles rapidly fuse with preexisting lysosomes and are converted to phagolysosomes (PL) that demonstrate both acid phosphatase and lactoperoxidase activities. The exposure of LPO-Iatex containing cells to 125-- and an extracellular peroxide-generating system, glucose oxidase-glucose, at 4°C leads to incorporation of label into TCA-precipitable material. The incorporated cell-associated label was present as monoiodotyrosine; negligible amounts were found in lipids. Cell viability remained\u3e 99%. Autoradiography at both the light and EM level revealed that \u3e 97% of the cells were labeled, and quantitative analysis demonstrated the localization of grains to LPO-latex containing PL. PL were separated on sucrose gradients, and their radiolabel was confined almost exclusively to the membrane rather than soluble contents

An extended hybrid density functional (X3LYP) with improved descriptions of nonbond interactions and thermodynamic properties of molecular systems

We derive here the form for the exact exchange energy density for a density that decays with Gaussian-type behavior at long range. This functional is intermediate between the B88 and the PW91 exchange functionals. Using this modified functional to match the form expected for Gaussian densities, we propose the X3LYP extended functional. We find that X3LYP significantly outperforms Becke three parameter Lee–Yang–Parr (B3LYP) for describing van der Waals and hydrogen bond interactions, while performing slightly better than B3LYP for predicting heats of formation, ionization potentials, electron affinities, proton affinities, and total atomic energies as validated with the extended G2 set of atoms and molecules. Thus X3LYP greatly enlarges the field of applications for density functional theory. In particular the success of X3LYP in describing the water dimer (with Re and De within the error bars of the most accurate determinations) makes it an excellent candidate for predicting accurate ligand–protein and ligand–DNA interactions

A candidate LiBH4 for hydrogen storage: Crystal structures and reaction mechanisms of intermediate phases

First-principles calculation and x-ray diffraction simulation methods have been used to explore crystal structures and reaction mechanisms of the intermediate phases involved in dehydriding of LiBH4. LiBH4 was found to dehydride via two sequential steps: first dehydriding through LiBH, followed by the dehydriding of LiBH through LiB. The first step, which releases 13.1 wt. % hydrogen, was calculated to have an activation barrier of 2.33 eV per formula unit and was endothermic by 1.28 eV per formula unit, while the second step was endothermic by 0.23 eV per formula unit. On the other hand, if LiBH4 and LiBH each donated one electron, possibly to the catalyst doped on their surfaces, it was found that the barrier for the first step was reduced to 1.50 eV. This implies that the development of the catalyst to induce charge migration from the bulk to the surface is essential to make LiBH4 usable as a hydrogen storage material in a moderate temperature range, which is also important to stabilize the low-temperature structure of Pnma (no. 62) LiBH on dehydrogenation. Consequently, the high 13.1 wt. % hydrogen available from the dehydriding of LiBH4 and LiBH and their phase stability on Pnma when specific catalysts were used suggest that LiBH4 has good potential to be developed as the hydrogen storage medium capable of releasing the Department of Energy target of 6.5 wt. % for a hydrogen fuel cell car in a moderate temperature range

The membrane proteins of the vacuolar system II. bidirectional flow between secondary lysosomes and plasma membrane

Lactoperoxidase covalently coupled to latex spheres (LPO-latex) has been used to selectively iodinate the phagolysosome (PL) membrane within living macrophages, as discussed in the accompanying article. This procedure labeled ~24 polypeptides in the PL membrane; these were similar to those iodinatable on the external surface of the plasma membrane (PM). We now report on the translocation and fate of these proteins when the cells are returned to culture. TCA-precipitable radioactivity was lost from cells with biphasic kinetics. 20-50% of the cell-associated radiolabel was rapidly digested (t1/2 ≅ 1 h) and recovered in the culture medium as monoiodotyrosine. 50-80% of the label was lost slowly from cells (t1/2 ≅ 24-30 h). Quantitative analysis of gel autoradiograms showed that all radiolabeled proteins were lost at the same rate in both the rapid and slow phases of digestion. Within 15-30 min after labeling of the PL membrane, EM autoradiography revealed that the majority of the cell-associated grains, which at time 0 were associated with PL, were now randomly dispersed over the plasmalemma. At this time, analysis of PM captured by a second phagocytic load revealed the presence of all labeled species originally present in the PL membrane. This demonstrated the rapid, synchronous centrifugal flow of PL polypeptides to the cell surface. Evidence was also obtained for the continuous influx of representative samples of the PM into the PL compartment by way of pinocytic vesicles. This was based on the constant flow of fluid phase markers into latex-containing PL and on the internalization of all iodinatable PM polypeptides into this locus. These observations provide evidence for the continuous, bidirectional flow of membrane polypeptides between the PM and the secondary lysosome and represent an example of a membrane flow and recycling mechanism

The membrane proteins of the vacuolar system I. analysis by a novel method of intralysosomal lodination

A method has been developed to deliver an iodinating system into the confines of the phagolysosome, allowing us to study the nature of the phagolysosomal membrane. Lactoperoxidase (LPO) is covalently coupled to carboxylated latex spheres (LPO-latex) in a stable, enzymatically active form. The addition of LPO-latex to cultured macrophages leads to their rapid attachment, ingestion, and enclosure in a plasma membrane-derived phagocytic vacuole. These organelles rapidly fuse with preexisting lysosomes and are converted to phagolysosomes (PL) that demonstrate both acid phosphatase and lactoperoxidase activities. The exposure of LPO-latex containing cells to 125l- and an extracellular peroxide-generating system, glucose oxidase-glucose, at 4°C leads to incorporation of label into TCA-precipitable material. The incorporated cell-associated label was present as monoiodotyrosine, and negligible amounts were found in lipids. Cell viability remained \u3e99%. Autoradiography at both the light and EM level revealed that \u3e97% of the cells were labeled, and quantitative analysis demonstrated the localization of grains to LPO-latex containing PL. PL were separated on sucrose gradients, and their radiolabel was confined almost exclusively to the membrane rather than soluble contents. SDS-polyacrylamide gel electrophoretic analysis of the peptides iodinated from within PL demonstrated at least 24 species with molecular weights ranging from 12,000 to 250,000. A very similar group of proteins was identified on the plasma membrane (PM) after surface iodination, and on latex phagosomes derived from iodinated PM. No novel proteins were detected in PL, either immediately after phagosome-lysosome fusion or after 1 h of intracytoplasmic residence. We conclude that the membrane proteins accessible to LPO-catalyzed iodination on the luminal surface of the PL and on the external face of the PM are similar, if not identical

c-Src drives intestinal regeneration and transformation

The non‐receptor tyrosine kinase c‐Src, hereafter referred to as Src, is overexpressed or activated in multiple human malignancies. There has been much speculation about the functional role of Src in colorectal cancer (CRC), with Src amplification and potential activating mutations in up to 20% of the human tumours, although this has never been addressed due to multiple redundant family members. Here, we have used the adult <i>Drosophila</i> and mouse intestinal epithelium as paradigms to define a role for Src during tissue homeostasis, damage‐induced regeneration and hyperplasia. Through genetic gain and loss of function experiments, we demonstrate that Src is necessary and sufficient to drive intestinal stem cell (ISC) proliferation during tissue self‐renewal, regeneration and tumourigenesis. Surprisingly, Src plays a non‐redundant role in the mouse intestine, which cannot be substituted by the other family kinases Fyn and Yes. Mechanistically, we show that Src drives ISC proliferation through upregulation of EGFR and activation of Ras/MAPK and Stat3 signalling. Therefore, we demonstrate a novel essential role for Src in intestinal stem/progenitor cell proliferation and tumourigenesis initiation <i>in vivo.</i&gt

Mechanism of the Stoddart-Heath Bistable Rotaxane Molecular Switch

We use quantum mechanics to characterize the structure and current−voltage performance of the Stoddart−Heath rotaxane-based programmable electronic switch. We find that the current when the ring is on the DNP is 37−58 times the current when the ring is on the TTF, in agreement with experiment (ratio of 10−100). This establishes the basis for iterative experimental−theoretical efforts to optimize systems for molecule-based electronics which we illustrate by predicting the effect of adding a group such as CN to the rotaxane

Endocytosis and the recycling of plasma membrane

[No abstract available