CALCIUM-INDUCED CHANGES IN ANNEXIN-V BEHAVIOR IN SOLUTION AS SEEN BY PROTON NMR-SPECTROSCOPY

The behaviour of human annexin V in the presence of calcium was studie d by NMR. We observe the formation of well defined dimers, as well as a change in the local dynamics of one His side chain. We assign the ob served changes to either His98 or His267 residues and conclude that th ey could be related either to the hinge-bending motion reported from c rystal structures, or to a local side chain rearrangement within the c alcium-binding loops concerned. Dimerization was also confirmed by a s mall-angle neutron-scattering experiment. Under the experimental condi tions used, we do not observe the conformational change involving Trp1 87 seen in previous studies, which occurs at higher relative calcium c oncentrations.