Oligomeric structure of bAE3 protein.

The "brain" form of the anion exchanger protein 3 (bAE3) has been purified to homogeneity from the rabbit kidney by differential centrifugation and immunoaffinity chromatography. A single protein band of approximately 165 kDa was detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Monomers, dimers (a major component), and a higher oligomeric form (apparently tetramers) were found after oxidative cross-linking of purified bAE3. The largest form of bAE3 was separated from dimers and monomers by sucrose gradient centrifugation and was studied by transmission electron microscopy to confirm a tetrameric structure. Two main types of bAE3 images were detected, round (approximately 11-14 nm) and square-shaped (approximately 12 x 12 nm). Image analysis revealed fourfold rotational symmetry of both the round and square-shaped images, indicating that bAE3 consists of multiples of 4 subunits. We conclude that bAE3 in Triton X-100 solution is predominantly a mixture of dimers and tetramers with a smaller amount of monomers.

[Some biochemical characteristics of substances from extracellular virus-like particles of the Gypsy retrotransposon (MDG4)]. / Issledovanie nekotorykh biokhimicheskikh kharkteristik preparatov vnekletochnykh virusopodobnykh chastits retrotranspozona Gypsy (Mdg4).

To investigate the gypsy functional activity, the possibility of conservation of its genetic information in VLP in the extracellular form has been examined. Preparations containing extracellular gypsy VLP from D. melanogaster and D. virilis were obtained. Non degradative full-sized polyA+ RNA and polyA+ RNA-DNA complexes of gypsy were revealed in the both preparations. The polypeptides with some specificity to gypsy nucleic acids were identified in VLP preparations. Some morphological and physical characteristics of the VLP preparations were obtained. The data obtained suggest the presence of non-degradative gypsy VLP in cultured media of D. melanogaster and D. virilis cells.

Trimeric forms of the photosystem I reaction center complex pre-exist in the membranes of the cyanobacterium Spirulina platensis.

Oligomeric and monomeric forms of chlorophyll-protein complexes of photosystem I (PSI) have been isolated from the mesophilic cyanobacterium Spirulina [(1992) FEBS Lett. 309, 340-342]. Electron microscopic analysis of the complexes showed that the oligomeric form is a trimer of the shape and dimensions similar to those of the trimer from thermophilic cyanobacteria. The chlorophyl ratio in the isolated trimer and monomer was found to be 7:3. The trimeric form of PSI complex in contrast to the monomeric one contains the chlorophyll emitting at 760 nm (77K), which is also found in Spirulina membranes and therefore could be used as an intrinsic probe for the trimeric complex. The 77K circular dichroism spectrum of the trimeric form is much more similar to that of Spirulina membranes than the spectrum of the monomer. Thus, the trimeric PSI complexes exist and dominate in the Spirulina membranes.

Cytochrome P-450: hexameric structure of the purified LM4 form.

Purified cytochrome P-450LM4 was found to be monodisperse in 20% glycerol by analytical ultracentrifugation. Its S20,w value was quite similar to that of hexameric P-450LM2. At lower glycerol concentrations the P-450LM4 showed a tendency to aggregate. The P-450LM4 oligomers were immobilized on Ultrogel A4 under conditions allowing only one covalent link to the matrix per oligomer. In the presence of SDS, the oligomers dissociated leaving only 1/6th of the initial amount of bound protein on the matrix, suggesting that the purified P-450LM4 is a hexamer. This was confirmed by electron microscopy. The quaternary structure of the P-450LM4 was similar to that demonstrated earlier for P-450LM2.

Presence of the gypsy (MDG4) retrotransposon in extracellular virus-like particles.

As a first step to investigate the functional activity of gypsy virus-like particles (VLPs) we explored the possibility of preservation of its VLP in extracellular form. The preparations containing extracellular gypsy VLP from Drosophila melanogaster and D. virilis were obtained. Full-length polyA+ RNA and polyA+ RNA-DNA complexes of gypsy were observed in both preparations. The polypeptides with some specificity to gypsy nucleic acids were identified in the obtained VLP preparations. These data accompanied by morphological characteristics of samples testify the presence of intact gypsy VLP in cultured media both from D. melanogaster and D. virilis cultivated cells.

[Analysis of the quaternary structure of secreted repressible acid phosphatase from the yeast Saccharomyces cerevisiae]. / Analiz chetvertichnoi struktury sekretiruemoi repressibel'noi kisloi fosfatazy drozhzhei Saccharomyces cerevisiae.

The structural organization of extracellular repressible acid phosphatase from S. cerevisiae has been studied. The existence of multiple acid phosphatase forms with isoelectric points at pH 4.1-4.8 has been confirmed by isoelectrofocusing. The molecular masses of three acid phosphatase isoforms (56, 57-59, and 60 kDa) obtained after enzymatic deglycosylation correlate with the data obtained previously during the analysis of translation products in cell-free systems. Electron microscopic studies revealed that the acid phosphatase molecule has a square shape and is made up of four identical subunits with molecular masses of about 125 kDa.

Isolation, crystallization in the macrogravitation field, preliminary X-ray investigation of uridine phosphorylase from Escherichia coli K-12.

Uridine phosphorylase (UPH) from Escherichia coli K-12 has been purified to near homogeneity from a strain harbouring the udp gene, encoding UPH, on a multicopy plasmid. UPH was purified to electrophoretic homogeneity with the specific activity 230 units/mg with a recovery of 80%, yielding 120 mg of enzyme from 3g cells. Crystals of enzyme suitable for X-ray diffraction analysis were obtained in a preparative ultracentrifuge. The packing of the molecules in the crystals may be described by the space group P2(1)2(1)2(1) with the unit cell constants a = 90.4; b = 128.8; c = 136.8 A. There is one molecule per asymmetric unit, Vm = 2.4. These crystals diffract to at least 2.5-2.7 A resolution. The hexameric structure of UPH was directly demonstrated by electron microscopy study and image processing.

The main adenosine triphosphate-binding component of amphibian oocytes is ferritin.

After fractionation of mitochondrion-free extracts of Xenopus laevis and Rana temporaria oocytes in sucrose gradients, a distinct peak of adenosine triphosphate (ATP)/guanosine triphosphate (GTP)-binding activity in the 50-70 S range has been detected. This substance has a boyant density in Cs2SO4 of 1.45 g/cm3. The nucleotide-binding substance has been purified to apparent homogenety. By means of electron microscopy, sodium dodecyl sulfate-electrophoresis and other methods it has been identified as ferritin.

Electron microscopy and image analysis of the GroEL-like protein and its complexes with glutamine synthetase from pea leaves.

The molecular structure of GroEL-like protein from pea leaves has been studied by electron microscopy and image analysis of negatively stained particles. Over 1500 molecular projections were selected and classified by multivariate statistical analysis. It was shown that the molecule consists of 14 subunits arranged in two layers with 72 point group symmetry. Side view projections of the molecule show a four-striation appearance, which subdivides both layers of seven subunits into two halves; this may be explained by a two-domain structure of the subunits. The presence in protein preparations of projections corresponding to one layer of subunits or half-molecules is consistent with the molecular structure suggested. Electron microscopic evidence for a specific association of GroEL-like protein and octameric glutamine synthetase, which was co-purified with this protein, was obtained.

Electron microscopy of the complexes of ribulose-1,5-bisphosphate carboxylase (Rubisco) and Rubisco subunit-binding protein from pea leaves.

The structure of ribulose-1,5-bisphosphate carboxylase (Rubisco) subunit-binding protein and its interaction with pea leaf chloroplast Rubisco were studied by electron microscopy and image analysis. Electron-microscopic evidence for the association of Rubisco subunit-binding protein, consisting of 14 subunits arranged with 72 point group symmetry, and oligomeric (L8S8) Rubisco was obtained.

[Quaternary structure of uridine phosphorylase from E. coli K-12]. / Chetvertichnaia struktura uridinfosforilazy iz E. coli K-12.

Uridine phosphorylase was isolated from E. coli K-12 cells in a homogeneous state. The molecular mass of the enzyme as determined by gel filtration corresponds, approximately, to a hexamer made up of 27.5 kDa monomers. Evidence for the hexameric structure of uridine phosphorylase was obtained by electron microscopy with numerical treatment of the images. The six monomers within the enzyme molecule are arranged in two layers, three monomers in each, at the apices of a triangular antiprism with a point group symmetry of 32.

[Physico-chemical characteristics of angiotensin-converting enzyme from the bovine lung]. / Fiziko-khimicheskie kharakteristiki angiotenzin-prevrashchaiushchego fermenta iz legkikh byka.

The angiotensin-converting enzyme from bovine lung was isolated by chromatography with a 25-30% yield and purified 2200-2600-fold. The active molecule concentration in the enzyme preparations was 70-100% as could be judged from titration by inhibitor SQ 20,881. The molecular mass of the enzyme according to electrophoretic data is about 132 kDa; the maximal radius of the enzyme molecule as determined by electron microscopy is 68 +/- 9 A. Five enzyme isoforms with pI of 4.85, 4.7, 4.54, 4.38 and 4.3, respectively, were identified. The kinetic parameters of hydrolysis of three synthetic peptide substrates and the constants of activation of the substrate (Z-Phe-His-Leu) hydrolysis by chloride anions were determined.

Negative staining of proteins.

Negative staining, some closely related alternative preparation techniques and radiation stability are considered. An attempt is made to clarify the mechanism of action and ultimate resolution limit of negative staining. The results of electron diffraction investigation of thermitase microcrystals embedded in glucose and glucose + stains are presented. It is shown that at doses not exceeding 10 electrons/nm2 electron diffraction from thermitase crystals demonstrate diffraction fields up to 0.2 nm. When adding heavy-atom salts to glucose or using negative staining, the relative intensities of reflections change and electron diffraction patterns for every type of heavy-atom additive (or negative stain) have their specific features. Such characteristic changes of reflection intensities indicate specific interaction of these additives (or stains) with the object. In the case of electron diffraction from the crystals stained using the routine negative staining technique the ordering was preserved down to 0.4-0.5 nm. Increasing the dose up to the normal value results in fading of distant reflections. Thus, negative staining with radiation doses less than the critical one could yield resolution down to 0.4 nm. Yet, the structure may change due to interaction with the stain. Nevertheless, the possibility that such resolution could be obtained for a limited number of objects should not be excluded. Some examples of the application of negative staining for investigation of quaternary and domain structure of proteins (nitrogenase, glutamine synthetase, mitochondrial ATP-synthase, membrane monooxygenase enzymes), tubular and two-dimensional protein crystals (catalase, phosphorylase, HWV protein, hydrogenase), as well as ribosomes and bacteriophages are given in the review.

Coenzyme non-specific glutamate dehydrogenase from Chlorella pyrenoidosa 82T: electron microscopic studies.

The constitutive coenzyme non-specific glutamate dehydrogenase (GDH) from Chlorella pyrenoidosa 82T was purified to homogeneity by column immunoaffinity chromatography and examined by an electron microscope. The enzyme molecule was found to be a hexameric oligomer composed of monomers arranged in three 2-point group symmetry in two layers slightly twisted round the 3-fold axis. The molecule is 8 +/- 1 nm in diameter and 10 +/- 1 nm in height. The enzyme molecules appear both to dissociate into trimers and to associate along the 3-fold axis forming linear aggregates under certain conditions. A tentative model of the Chlorella GDH molecule is proposed, which is very similar to those described for bovine liver GDH and GDH from Clostridium symbiosum.

Structure of the ATP-synthase studied by electron microscopy and image processing.

The structure of ATP synthase from beef heart mitochondria has been studied by electron microscopy and image processing using negatively stained specimens of detergent-solubilized and membrane-bound molecules. The F1-ATPase and the membrane-embedded F0 sector of ATP synthase are found to be connected by a narrow stalk, 4-4.5 nm long and 3-3.5 nm wide, projecting about 4.2 nm from the membrane surface. The F0 sector has a globular shape, 6-8 nm in diameter and, in part, extends from the membrane lipid bilayer.