Biomedical subjects

A Engel

Publications and source records attributed to A Engel.

At least 73 records · Page 4Linked to original sources

PubMed2000

Elevated levels of lipoprotein(a) in familial bone marrow edema syndrome of the hip.

There is controversy whether bone marrow edema syndrome represents a distinct transient disease or reflects an early reversible phase of spontaneous osteonecrosis of the hip. Hypofibrinolysis on the basis of elevated plasma levels of plasminogen activator inhibitor or lipoprotein(a) or both has been reported to favor the development of bone marrow edema syndrome and nontraumatic avascular necrosis. The current authors report on the familial occurrence of transient bone marrow edema syndrome of the hip in three female family members. Plasma concentrations of lipoprotein(a) were elevated in all three patients, whereas serum levels of plasminogen activator inhibitor were within normal ranges. This first familial description of transient bone marrow edema syndrome of the hip strongly suggests that a genetically determined elevation of lipoprotein(a) may be an important predisposing factor in these patients.

Adult↗

PubMed2000

Planform selection in two-layer Benard-marangoni convection

Benard-Marangoni convection in a system of two superimposed liquids is investigated theoretically. Extending previous studies, the complete hydrodynamics of both layers is treated and buoyancy is consistently taken into account. The planform selection problem between rolls, squares, and hexagons is investigated by explicitly calculating the coefficients of an appropriate amplitude equation from the parameters of the fluids. The results are compared with recent experiments on two-layer systems in which squares at onset have been reported.

Journal Article↗

PubMed2000

Perforated colonic cancer. Evolution and prognosis.

OBJECTIVE: The purpose of this study was to determine whether patients with perforating colonic cancer, among patients who need emergency surgery, should be considered to comprise a group with a worse prognosis. METHODS: We retrospectively revised the clinical records for 91 cases of emergency primary resection for carcinoma of the colon, of which 22 were perforating (4 Dukes A, 10 Dukes B and 8 Dukes C) and 69 were obstructive (3 Dukes A, 30 Dukes B and 36 Dukes C). For purposes of comparison we also analyzed a synchronous series of 112 patients who underwent elective surgery. RESULTS: There were no recurrences or deaths among the 7 patients with Dukes A disease (follow-up from 6 to 90 months), so these patients were excluded. In the 84 remaining emergency patients, 38 showed progression of the disease (13 local recurrence, 17 liver metastases, 4 lung, 3 peritoneal and 1 bone metastases). There were 26 deaths (6 patients with perforating and 20 with obstructive disease). There was no significant difference in survival or disease progression between patients with perforating and obstructive disease. CONCLUSIONS: These results do not support the classical view of considering perforating cancer as a type with an especially ominous prognosis among patients who require emergency surgery.

Adult↗

PubMed2000

Fibromyalgia, hypermobility, and breast implants.

OBJECTIVE: To examine possible relationships among fibromyalgia (FM, American College of Rheumatology 1990 criteria), hypermobility, and breast implants. METHODS: The medical records of 2,500 female patients (ages 25-65) who had been seen for the first time in a rheumatology practice in Atlanta, GA, during 1986-92 were abstracted and analyzed. In each analysis, patients whose records indicated that the patient met the full case criteria were compared with patients whose records had no indication of the disease. Patients whose medical records indicated the clinical onset of FM prior to breast implantation were identified. RESULTS: Univariate and multivariate regression analyses were performed, adjusting for age, income, and the presence of connective tissue disease or rheumatoid arthritis. Significant associations were found between hypermobility and FM (adjusted OR 2.20, 95% CI 1.73, 2.80) and between hypermobility and breast implantation (adjusted OR 1.80, 95% CI 1.19, 2.69). No association was found between breast implantation and subsequent FM (adjusted OR 0.74, 95% CI 0.42, 1.32). CONCLUSION: Hypermobility was found to be independently associated with both FM and with breast implantation, but FM and breast implantation were not found to be independently associated with each other.

Adult↗

PubMed1999

Charting the surfaces of the purple membrane.

The preponderance of structural data of the purple membrane from X-ray diffraction (XRD), electron crystallography (EC), and atomic force microscopy (AFM) allows us to ask questions about the structure of bacteriorhodopsin itself, as well as about the information derived from the different techniques. The transmembrane helices of bacteriorhodopsin are quite similar in both EC and XRD models. In contrast, the loops at the surfaces of the purple membrane show the highest variability between the atomic models, comparable to the height variance measured by AFM. The excellent agreement of the AFM topographs with the atomic models from XRD builds confidence in the results. Small technical difficulties in EC lead to poorer resolution of the loop structures, although the combination of atomic models with AFM surfaces allows clear interpretation of the extent and flexibility of the loop structures. While XRD remains the premier technique to determine very-high-resolution structures, EC offers a method to determine loop structures unhindered by three-dimensional crystal contacts, and AFM provides information about surface structures and their flexibility under physiological conditions.

Amino Acid Motifs↗

PubMed1999

Purification and electron microscopic characterization of the membrane subunit (IICB(Glc)) of the Escherichia coli glucose transporter.

The glucose transporter of the bacterial phosphotransferase system mediates sugar transport across the cytoplasmic membrane concomitant with sugar phosphorylation. It consists of a cytoplasmic subunit IIA(Glc) and the transmembrane subunit IICB(Glc). IICB(Glc) was purified to homogeneity by urea/alkali washing of membranes and nickel-chelate affinity chromatography. About 1.5 mg highly pure IICB(Glc) representing 77% of the total activity present in the membranes was obtained from 8g (wet weight) of cells. IICB(Glc) was reconstituted into lipid bilayers by temperature-controlled dialysis to yield small 2D crystals and by a rapid detergent-dilution procedure to yield densely packed vesicles. Electron microscopy and digital image processing of the negatively stained 2D crystals revealed a trigonal lattice with a unit cell size of a = b = 14.5 nm. The unit cell morphology exhibited three dimers of IICB(Glc) surrounding the threefold symmetry center. Single particle analysis of IICB(Glc) in proteoliposomes obtained by detergent dialysis also showed predominantly dimeric structures.

Chromatography, Affinity↗

PubMed1999

The structure of aquaporin-1 at 4.5-A resolution reveals short alpha-helices in the center of the monomer.

Aquaporin-1 is a water channel found in mammalian red blood cells that is responsible for high water permeability of its membrane. Our electron crystallographic analysis of the three-dimensional structure of aquaporin-1 at 4.5-A resolution confirms the previous finding that each subunit consists of a right-handed bundle of six highly tilted transmembrane helices that surround a central X-shaped structure. In our new potential map, the rod-like densities for the transmembrane helices show helically arranged protrusions, indicating the positions of side chains. Thus, in addition to the six transmembrane helices, observation of helically arranged side-chain densities allowed the identification of two short alpha-helices representing the two branches of the central X-shaped structure that extend to the extracellular and cytoplasmic membrane surfaces. The other two branches are believed to be loops connecting the short alpha-helix to a neighboring transmembrane helix. A pore found close to the center of the aquaporin-1 monomer is suggested to be the course of water flow with implications for the water selectivity.

Aquaporin 1↗

PubMed1999

Controlled unzipping of a bacterial surface layer with atomic force microscopy.

We have combined high-resolution atomic force microscopy (AFM) imaging and force spectroscopy to gain insight into the interaction forces between the individual protomers of the hexagonally packed intermediate (HPI) layer of Deinococcus radiodurans. After imaging the HPI layer, the AFM stylus was attached to individual protomers by enforced stylus-sample contact to allow force spectroscopy experiments. Imaging of the HPI layer after recording force-extension curves allowed adhesion forces to be correlated with structural alterations. By using this approach, individual protomers of the HPI layer were found to be removed at pulling forces of approximately 300 pN. Furthermore, it was possible to sequentially unzip entire bacterial pores formed by six HPI protomers. The combination of high-resolution AFM imaging of individual proteins with the determination of their intramolecular forces is a method of studying the mechanical stability of supramolecular structures at the level of single molecules.

Gram-Positive Cocci↗

PubMed1999

High resolution AFM topographs of the Escherichia coli water channel aquaporin Z.

Aquaporins form a large family of membrane channels involved in osmoregulation. Electron crystallography has shown monomers to consist of six membrane spanning alpha-helices confirming sequence based predictions. Surface exposed loops are the least conserved regions, allowing differentiation of aquaporins. Atomic force microscopy was used to image the surface of aquaporin Z, the water channel of Escherichia coli. Recombinant protein with an N-terminal fragment including 10 histidines was isolated as a tetramer by Ni-affinity chromatography, and reconstituted into two-dimensional crystals with p42(1)2 symmetry. Small crystalline areas with p4 symmetry were found as well. Imaging both crystal types before and after cleavage of the N-termini allowed the cytoplasmic surface to be identified; a drastic change of the cytoplasmic surface accompanied proteolytic cleavage, while the extracellular surface morphology did not change. Flexibility mapping and volume calculations identified the longest loop at the extracellular surface. This loop exhibited a reversible force-induced conformational change.

Amino Acid Sequence↗

PubMed1999

Structure of the water channel AqpZ from Escherichia coli revealed by electron crystallography.

Molecular water channels (aquaporins) allow living cells to adapt to osmotic variations by rapid and specific diffusion of water molecules. Aquaporins are present in animals, plants, algae, fungi and bacteria. Here we present an electron microscopic analysis of the most ancient water channel described so far: the aquaporin Z (AqpZ) of Escherichia coli. A recombinant AqpZ with a poly(histidine) tag at the N terminus has been constructed, overexpressed and purified to homogeneity. Solubilized with octylglucoside, the purified AqpZ remains associated as a homotetramer, and assembles into highly ordered two-dimensional tetragonal crystals with unit cell dimensions a = b = 95 A, gamma = 90 degrees when reconstituted by dialysis in the presence of lipids. Three-dimensional reconstruction of negatively stained lattices revealed the p42(1)2 packing arrangement that is also observed with the human erythrocyte water channel (AQP1). The 8 A projection map of the AqpZ tetramer in frozen hydrated samples is similar to that of AQP1, consistent with the high sequence homology between these proteins.

Aquaporin 1↗

PubMed1999

Domain organization of Mac-2 binding protein and its oligomerization to linear and ring-like structures.

The multidomain Mac-2 binding protein (M2BP) is present in serum and in the extracellular matrix in the form of linear and ring-shaped oligomers, which interact with galectin-3, fibronectin, collagens, integrins and other large glycoproteins. Domain 1 of M2BP (M2BP-1) shows homology with the cysteine-rich SRCR domain of scavanger receptor. Domains 2 and 3 are related to the dimerization domains BTB/POZ and IVR of the Drosophila kelch protein. Recombinant M2BP, its N-terminal domain M2BP-1 and a fragment consisting of putative domains 2, 3 and 4 (M2BP-2,3,4) were investigated by scanning transmission electron microscopy, transmission electron microscopy, analytical ultracentrifugation and binding assays. The ring oligomers formed by the intact protein are comprised of approximately 14 nm long segments composed of two 92 kDa M2BP monomers. Although the rings vary in size, decamers predominate. The various linear oligomers also observed are probably ring precursors, dimers predominate. M2BP-1 exhibits a native fold, does not oligomerize and is inactive in cell attachment. M2BP-2,3,4 aggregates to heterogeneous, protein filled ring-like structures as shown by metal shadowed preparations. These aggregates retain the cell-adhesive potential indicating native folding. It is hypothesized that the rings provide an interaction pattern for multivalent interactions of M2BP with target molecules or complexes of ligands.

Amino Acid Sequence↗

PubMed1999

The reaction center complex from the green sulfur bacterium Chlorobium tepidum: a structural analysis by scanning transmission electron microscopy.

The three-dimensional (3D) structure of the reaction center (RC) complex isolated from the green sulfur bacterium Chlorobium tepidum was determined from projections of negatively stained preparations by angular reconstitution. The purified complex contained the PscA, PscC, PscB, PscD subunits and the Fenna-Matthews-Olson (FMO) protein. Its mass was found to be 454 kDa by scanning transmission electron microscopy (STEM), indicating the presence of two copies of the PscA subunit, one copy of the PscB and PscD subunits, three FMO proteins and at least one copy of the PscC subunit. An additional mass peak at 183 kDa suggested that FMO trimers copurify with the RC complexes. Images of negatively stained RC complexes were recorded by STEM and aligned and classified by multivariate statistical analysis. Averages of the major classes indicated that different morphologies of the elongated particles (length=19 nm, width=8 nm) resulted from a rotation around the long axis. The 3D map reconstructed from these projections allowed visualization of the RC complex associated with one FMO trimer. A second FMO trimer could be correspondingly accommodated to yield a symmetric complex, a structure observed in a small number of side views and proposed to be the intact form of the RC complex.

Bacterial Proteins↗

PubMed1999

Secretin PulD: association with pilot PulS, structure, and ion-conducting channel formation.

The outer membrane protein PulD (secretin) of Klebsiella oxytoca is required for transport of pullulanase across this membrane. We have purified a multimeric PulD complex from an Escherichia coli strain expressing all the proteins involved in pullulanase secretion. The outer membrane-anchored lipoprotein PulS was found to copurify with PulD. The molar ratio of the two proteins is close to 1:1, and the size of the complex is approximately 1 MDa. Scanning transmission electron and cryo-electron microscopy analyses showed that the purified complex is a cylindrical structure having a central cavity of approximately 7.6 nm and peripheral radial spokes. Fusion of proteoliposomes containing the purified complex with a planar lipid bilayer resulted in the appearance of small, voltage-activated, ion-conducting channels. We conclude that the central cavity seen in the electron microscope is part of a large gated channel and propose that the observed current fluctuations correspond to voltage-induced, relatively minor displacements of domains in the purified complex rather than to a complete opening of the secretin channel.

Bacterial Outer Membrane Proteins↗

PubMed1999

Novel molecular architecture of the multimeric archaeal PEP-synthase homologue (MAPS) from Staphylothermus marinus.

The phosphoenolpyruvate (PEP)-synthases belong to the family of structurally and functionally related PEP-utilizing enzymes. The only archaeal member of this family characterized thus far is the Multimeric Archaeal PEP-Synthase homologue from Staphylothermus marinus (MAPS). This protein complex differs from the bacterial and eukaryotic representatives characterized to date in its homomultimeric, as opposed to dimeric or tetrameric, structure. We have probed the molecular architecture of MAPS using limited proteolytic digestion in conjunction with electron microscopic, biochemical, and biophysical techniques. The 2.2 MDa particle was found to be organized in a concentric fashion. The 93.7 kDa monomers possess a pronounced tripartite domain structure and are arranged such that the N-terminal domains form an outer shell, the intermediate domains form an inner shell, and the C-terminal domains form a core structure responsible for the assembly into a multimeric complex. The core domain was shown to be capable of assembling into the native multimer by recombinant expression in Escherichia coli. Deletion mutants as well as a synthetic peptide were investigated for their state of oligomerization using native polyacrylamide gel electrophoresis, molecular sieve chromatography, analytical ultracentrifugation, circular dichroism (CD) spectroscopy, and chemical cross-linking. Our data confirmed the existence of a short C-terminal, alpha-helical oligomerization motif that had been suggested by multiple sequence alignments and secondary structure predictions. We propose that this motif bundles the monomers into six groups of four. An additional formation of 12 dimers between globular domains from different bundles leads to the multimeric assembly. According to our model, each of the six bundles of globular domains is positioned at the corners of an imaginary octahedron, and the helical C-terminal segments are oriented towards the centre of the particle. The edges of the octahedron represent the dimeric contacts. Phylogenetic analysis suggests that the ancient predecessor of this family of enzymes contained the C-terminal oligomerization motif as a feature that was preserved in some hyperthermophiles.

Amino Acid Sequence↗

PubMed1999

Mitochondrial Lon of Saccharomyces cerevisiae is a ring-shaped protease with seven flexible subunits.

Lon (or La) is a soluble, homooligomeric ATP-dependent protease. Mass determination and cryoelectron microscopy of pure mitochondrial Lon from Saccharomyces cerevisiae identify Lon as a flexible ring-shaped heptamer. In the presence of ATP or 5'-adenylylimidodiphosphate, most of the rings are symmetric and resemble other ATP-driven machines that mediate folding and degradation of proteins. In the absence of nucleotides, most of the rings are distorted, with two adjacent subunits forming leg-like protrusions. These results suggest that asymmetric conformational changes serve to power processive unfolding and translocation of substrates to the active site of the Lon protease.

ATP-Dependent Proteases↗

PubMed1999

[Malignant nodular hidradenoma--sweat gland tumor].

Malignant hidradenoma is a very rare tumor that originates from sweat glands. We present a 61-year-old man with an ulcerated tumor in his right flank, 4 cm in diameter, that was excised with a wide free margin. Histopathologic study showed an ill-defined, epithelial neoformation, formed by lobules of clear polygonal cells in the deep dermis and subcutaneous tissue, diagnosed as malignant nodular hidradenoma. 1.5 years after excision there was enlargement of the right axillary and inguinal lymph nodes, which showed metastatic, adnexal neoplastic cells. Axillary resection and superficial dissection of the right inguinal nodes were performed. After 3 months the tumor had spread to other lymph nodes and acute obstructive renal failure required insertion of a pig-tail catheter into the right ureter. Radiotherapy was followed by chemotherapy, but he died from end-stage metastatic disease in multi-organ failure.

Adenoma, Sweat Gland↗

PubMed1999

Atomic force microscopy: a forceful way with single molecules.

The atomic force microscope (AFM) now routinely provides images that reveal subnanometer surface structures of biomolecules. The sensitivity and precision of AFM provide new opportunities for studying the mechanical properties of biomolecules and their interactions in their native environment.

Microchemistry↗

PubMed1999

Surface structures of native bacteriorhodopsin depend on the molecular packing arrangement in the membrane.

Bacteriorhodopsin is the one of the best-studied models of an ion pump. Five atomic models are now available, yet their comparison reveals differences of some loops connecting the seven transmembrane alpha-helices. In an attempt to resolve this enigma, topographs were recorded in aqueous solution with the atomic force microscope (AFM) to reveal the most native surface structure of bacteriorhodopsin molecules in the purple membrane. Individual peptide loops were observed with a lateral resolution of between 4.5 A and 5.8 A, and a vertical resolution of about 1 A. The AFM images demonstrate for the first time, that the shape, the position, and the flexibility of individual polypeptide loops depend on the packing arrangement of bacteriorhodopsin molecules in the lipid bilayer.

Bacteriorhodopsins↗