Search PubMed⌕ Search

Biomedical subjects

L Makowski

Publications and source records attributed to L Makowski.

47 records · Page 3Linked to original sources
PubMed1984

Gap junction structures. VI. Variation and conservation in connexon conformation and packing.

Correlation of structural changes in isolated gap junctions with the mechanism of channel gating is complicated by the effects of isolation procedures and the lack of a direct functional assay. The effect of variations in the isolation procedure are examined by comparison of the structures of gap junctions isolated by different protocols. X-ray diffraction data from over two hundren specimens are compared to provide a basis for identification of invariant aspects of the connexon structure and variable properties related either to functional switching or experimental modifications. We discuss the relationship between subunit tilt, lattice symmetry and packing, and membrane curvature and demonstrate that membrane curvature may be a natural consequence of the structure of the connexons and the patterns of interactions between them.

Animals↗
PubMed1984

Electronmicroscopy and circular dichroism of the dynamics of the formation and dissolution of supramolecular forms of Z-DNA.

Previous electronmicroscopic studies had shown that N-acetylaminofluorene (AFF)-substituted poly(dG-dC)-poly(dG-dC) in the Z conformation, in 10mM Mg++, condensed into periodically banded, branched structures. We now show that similar structures are seen when poly(dG-dC)-poly(dG-dC) is converted to the Z conformation by heating to 60 degrees C in 1mM Mn++ or to 65 degrees in the presence of 0.5mM Mn++. We demonstrate that these banded structures form in solution, i.e. they are not artifacts of the preparative procedures used for electronmicroscopy, by crosslinking the Z conformers in solution with DL-diepoxybutane (DEB), and then restoring the solution to conditions that favor return to the B conformation. Circular dichroism (CD) and immunochemical studies showed that the Z conformation was maintained and the banded supramolecular structures were still seen by electronmicroscopy. Electronmicroscopy and CID were also used to follow the dissolution of the supramolecular structures by controlled scission of the crosslinks with the eventual return to the short double stranded molecules typical of the B conformers. During this process, supercoiled structures, both toroidal and interwound, were observed. The relationship of the toroids to the banded structure is discussed in the context of two possible structures for the condensed polynucleotide. We conclude that DNA, whether in the B or Z conformation, is extremely flexible in the presence of appropriate counter ions, and we present evidence that earlier estimates of their persistence lengths are too high. The inherent tendency to form condensed, highly organized structures is a property of DNA that could play an important role in its "packaging," and in its functions, and might have been critical for the evolution and replication of early life forms.

2-Acetylaminofluorene↗
PubMed1980

Structural studies of the assembly of simple viruses.

The principles of structural design and the bonding properties of structural proteins form a basis for the study of virus assembly. Virus coat proteins are designed specifically to interact with one another and with the viral nucleic acid to form a stable virus particle. The process of assembly is controlled by the switching of protein subunit conformation, which can alter the binding properties of the subunits. The self-assembly processes of several simple viruses in vitro have significantly different rates of assembly and specificities for their viral nucleic acid. It is possible that many viruses have multiple pathways for assembly, each pathway exhibiting somewhat different characteristics but all resulting in identical infectious virus particles.

Bacteriophages↗
PubMed1980

Helical viruses.

Explore the source record for details and available documents.

Bacteriophages↗
PubMed1977

Gap junction structures. I. Correlated electron microscopy and x-ray diffraction.

X-ray crystallographic methods and electron microscope image analysis have been used to correlate the structure and the chemical composition of gap junction plaques isolated intact from mouse liver. The requirement that the interpretations of X-ray, electron microscope, and chemical measurements be consistent reduces the uncertainties inherent in the separate observations and leads to a unified picture of the gap junction structures. Gap junctions are built up of units called connexons that are hexagonally arrayed in the pair of connected cell membranes. X-ray diffraction and electron microscope measurements show that the lattice constant of this array varies from about 80 to 90 A. Analysis of electron micrographs of negatively stained gap junctions shows that there is significant short range disorder in the junction lattice. even though the long range order of the array is remarkably regular. Analysis of the disorder provides information about the nature of the intermolecular forces that hold the array together.

Animals↗
PubMed1977

Gap junction structures. II. Analysis of the x-ray diffraction data.

Models for the spatial distribution of protein, lipid and water in gap junction structures have been constructed from the results of the analysis of X-ray diffraction data described here and the electron microscope and chemical data presented in the preceding paper (Caspar, D. L. D., D. A. Goodenough, L. Makowski, and W.C. Phillips. 1977. 74:605-628). The continuous intensity distribution on the meridian of the X-ray diffraction pattern was measured, and corrected for the effects of the partially ordered stacking and partial orientation of the junctions in the X-ray specimens. The electron density distribution in the direction perpendicular to the plane of the junction was calculated from the meridional intensity data. Determination of the interference function for the stacking of the junctions improved the accuracy of the electron density profile. The pair-correlation function, which provides information about the packing of junctions in the specimen, was calculated from the interference function. The intensities of the hexagonal lattice reflections on the equator of the X-ray pattern were used in coordination with the electron microscope data to calculate to the two-dimensional electron density projection onto the plane of the membrane. Differences in the structure of the connexons as seen in the meridional profile and equatorial projections were shown to be correlated to changes in lattice constant. The parts of the junction structure which are variable have been distinguished from the invariant parts by comparison of the X-ray data from different specimens. The combination of these results with electron microscope and chemical data provides low resolution three- dimensional representations of the structures of gap junctions.

Animals↗