Gap junction structures: Analysis of the x-ray diffraction data

Abstract

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 the two-dimensional electron density projection onto the plane of the membrane. Differences in the structure of the connexons as seen in the meridional profiles 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 X-ray data from different specimens. The combination of these results with electron microscope and chemical data provides low-resolution threedimensional representations of the structures of gap junctions.The structural variations detailed in the preceding paper (5) establish that we are looking at not one structure of the gap junction, but at a family of structures. By observing closely related states of a molecular assembly, it is often possible to infer something about the way that transitions occur between states. These molecular rearrangements may be significant in the functional activity of the structure. Furthermore, polymorphism provides a constraint on the interpretation of the diffraction patterns. For example, the connexon structure is likely to be similar in arrays with different lattice constants, although the intensities in the X-ray patterns may be quite different.

Incompatibility of connexin 40 and 43 Hemichannels in gap junctions between mammalian cells is determined by intracellular domains.

“…The functional cell-to-cell channel is formed by docking of two hemichannels or connexons. Each connexon is composed of six connexin subunits (Makowski et al, 1977;Yeager and Gilula, 1992). Intercellular channels are defined as homotypic when the hemichannels contributed by each cell are composed of the same type of connexin or as heterotypic when each hemichannel is built up of a different type of connexin.…”

Calcium-mediated changes in gap junction structure: evidence from the low angle X-ray pattern.

“…The mechanism of the transition between the open and closed states of the channel is not known. However, studies of isolated, hexagonally ordered, gap junctions suggest it may involve a change in conformation of the connexon in the space between the two plasma membranes (1,7) or, alternatively, a coordinated rearrangement of the connexon subunits around the channel (14).…”

Gap junction channel structure in the early 21st century: facts and fantasies

“…The primary tools for structure analysis of gap junction channels include electron microscopy and image analysis [4][5][6][7][8][9], X-ray diffraction [10][11][12], nuclear magnetic resonance (NMR) spectroscopy [13][14][15] and atomic force microscopy (AFM) [16][17][18]. Mutagenic, biochemical and electrophysiological approaches have also been used to elucidate the structure-function relationships of gap junction channels.…”