α-Mannosidase from jack bean (Canavalia Ensiformis): Negative staining of single molecules and paracrystalline forms

Ubiquitous soluble Mg(2+)-ATPase complex. A structural study

We have performed a detailed structural analysis of the soluble Mg(2+)-ATPase complex purified from Xenopus laevis ovary, which is an abundant and ubiquitous homo-oligomeric protein complex located in the nucleus and in the cytoplasm, belonging to a novel multigene-family of putative Mg(2+)-ATPases. Enzyme activity staining after non-denaturing polyacrylamide gel electrophoresis revealed that Mg(2+)-ATPase activity of the native protein is dependent on oligomerization and could not be detected in dissociated subunits. For the native protein a sedimentation coefficient of 15.3 S and a corresponding relative molecular mass of 612,000 was determined by analytical ultracentrifugation and a relative molecular mass of 590,000 was estimated from scanning transmission electron microscopy, supporting our previous conclusion that the oligomer comprises six 97,000 Mr subunits. Conventional electron microscopy of negatively stained specimens revealed the Mg(2+)-ATPase complex to be a hexagonal molecule in its favoured "end-on" projection and a double-banded molecule in its "side-on" projection (approx. 12 nm diameter; approx. 9 nm height). In addition, dimerized complexes could be observed in negatively stained specimens, yielding pronounced hexameric images and four-banded images in their end-on and side-on orientations, respectively (approx. 12 nm diameter; approx. 18.5 nm height). Two-dimensional (2D = mono-molecular) crystals have been produced from the dimerized complexes by the negative staining carbon film technique. Hexagonal crystals with a p6 plane group symmetry were obtained from molecules in their end-on orientation and longitudinal arrays with a p2 symmetry from complexes in their side-on orientation. A low-resolution molecular model of the native protein, derived from averages of these two 2D crystals, is presented. From our results we propose oligomerization as an inherent structural principle of organization for this whole newly defined Mg(2+)-ATPase multigene-family, that includes such seemingly diverse functionally defined proteins as mammalian and yeast "vesicle fusion" and "peroxisome assembly" proteins and the product of the yeast cell cycle gene CDC48.

Negative staining-carbon film technique: new cellular and molecular applications

Two techniques are presented which extend the original negative staining-carbon film technique into new areas of cellular and molecular application. These relate (1) to the production of negatively stained specimens of single-layer plasma membrane split from intact cells during the overall procedure that are negatively stained from the cytoplasmic face and (2) to the production of negatively stained specimens directly from glycerol-containing protein solutions, membrane or viral suspensions. In both cases in vacuo drying onto mica from glycerol is performed, prior to deposition of a carbon film. (For the cellular technique, freshly cleaved mica is firstly rendered positively charged by immersion in Alcian blue.) This is followed by release of the carbon film plus adsorbed membrane or protein by floating onto water, with subsequent negative staining. Selected preliminary applications using human erythrocyte membrane and the high molecular weight (native) human erythrocyte tripeptidyl peptidase-II complex are given and considered speculation as to the future application of the techniques is provided.