2-DIMENSIONAL STRUCTURE OF MEMBRANE-BOUND ANNEXIN-V AT 8-ANGSTROM RESOLUTION

Two-dimensional (2-D) crystals of annexin V, grown by specific binding to phosphatidylserine containing planar lipid films, were studied by electron image analysis. Images of negatively stained two-dimensional crystals showed diffraction peaks extending to 11 Angstrom. After corr ecting lattice distorsions and averaging over several crystalline area s, the resolution of the analysis was extended up to 8 Angstrom. Obser ved along a direction perpendicular to the membrane plane, the four ho mologous domains characteristic of annexin V exhibit a noticeable diff erence in their distribution of protein density. An unambiguous assign ment of the domains was possible due to the similar packing of annexin V molecules in the 2-D crystals and in a 3-D crystal form with pseudo -R3 symmetry. The domains I and IV (numbering according to Huber et al ., Embo J., 1990, 9, 3867-3874) appear well resolved. On the other han d, the two other domains, II and III, present an almost continuous den sity, with a protrusion extending outwards the annexin V molecule. In addition, no hydrophilic opening is resolved at the center of the mole cule, yet a stain-filled 13-Angstrom structure is present, surrounded by domains I, II, and IV and distant by 5 Angstrom from the center of the molecule. We interpret these structural features as reflecting a c onformational change in the annexin V structure resulting from its mem brane binding. (C) 1994 Academic Press, Inc.