THE HIGH-RESOLUTION CRYSTAL-STRUCTURE OF HUMAN ANNEXIN-III SHOWS SUBTLE DIFFERENCES WITH ANNEXIN-V

The structure of recombinant human annexin III was solved to 1.8 Angst rom resolution. Though homologous to annexin I and V, the annexin III structure shows significant differences. The tryptophan in the calcium loop of the third domain is exposed to the solvent, as in the structu re of annexin V crystallized in high calcium concentrations, although the annexin UI crystals were prepared at low calcium concentrations. T he position of domain III relative to the other domains is different f rom both annexin V and I, suggesting further flexibility of the molecu le. The entire N-terminus of the protein is well-defined in the presen t structure. The side chain of tryptophan 5 interacts with the hinge r egion of the hydrophillic channel, which could have an effect on the p otential mobility of this region, as well as on its possible calcium c hannel behavior.