Calcium-dependent changes in properties of human prothrombin: a study using high-performance size-exclusion chromatography and gel-permeation chromatography

Purification and partial characterization of the Rhizobium leguminosarum biovar viciae Ca2+-dependent adhesin, which mediates the first step in attachment of cells of the family Rhizobiaceae to plant root hair tips

The Ca2+-dependent adhesin which mediates the first step in attachment of bacteria of the family Rhizobiaceae to plant root hair tips was isolated from the surface of Rhizobium leguminosarum biovar viciae cells; its ability to inhibit attachment of R. leguminosarum to pea root hair tips was used as a bioassay. Isolated adhesin was found to be able to inhibit attachment of both carbon-limited and manganese-limited R. leguminosarum cells. A multicolumn purification procedure was developed which resulted in pure adhesin, as judged from silver staining of isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electropherograms. The crucial step in purification was the elution of rhizobial proteins by a CaCl2 gradient from a hydroxyapatite matrix. The specific activity increased 1,250 times during purification. The isoelectric point of the adhesin was determined to be 5.1, and the molecular mass was 14 kilodaltons (kDa), as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. By using gel filtration in the presence and absence of Ca2+, the molecular mass of the adhesin was determined to be 15 and 6 kDa, respectively. The adhesin appeared to be a calcium-binding protein. The purified adhesin inhibited attachment of various other rhizobia to pea root hair tips. Also, cell surface preparations of several other rhizobial strains, including Agrobacterium, Bradyrhizobium, and Phyllobacterium spp., showed adhesin activity, suggesting that a common plant receptor is used for attachment of Rhizobiaceae cells and that the adhesin is common among Rhizobiaceae. No attachment-inhibiting activity was detected in cell surface preparations from various other bacterial strains tested. Cell surface preparations from Sym or Ti plasmid-cured Rhizobium and Agrobacterium strains, respectively, also showed adhesin activity, indicating that Sym or Ti plasmid-borne genes are not required for the synthesis and biogenesis of the adhesin. The adhesin was also found to be involved in the attachment of rhizobia to the root hairs of various other legumes and nonlegume plants, including monocotyledonous ones. Since the adhesin appears to be specific for Rhizobiaceae and is Ca2+ dependent, we propose to designate it rhicadhesin. A more detailed model for rhizobial attachment to plant root hairs is discussed.

A hydrophobic site in human prothrombin present in a calcium-stabilized conformer

Human prothrombin and prothrombin fragment 1 were demonstrated to bind to Phenyl-TSK columns in the presence of 5.0 mM calcium ions but not in the presence of either magnesium ions or manganese ions. The calcium-dependent interaction of prothrombin fragment 1 is markedly reduced upon oxidation of approximately one mole of tryptophan per mole of protein. The ability of prothrombin fragment 1 to inhibit prothrombin activation by factor Xa in the presence of calcium ions and phospholipid is also markedly reduced by reaction with N-bromosuccinimide. These results provide the first demonstration of a calcium-specific site in prothrombin outside of the "GLA domain".