Solution structure of Ca 2+ -free rat a-parvalbumin

摘要: Mammals express two parvalbumins—an a isoform and b isoform. In rat, the a-parvalbumin (a-PV) exhibits superior divalent ion affinity. For example, standard free energies for Ca 2+ binding differ by 5.5 kcal/mol in 0.15 M KCl (pH 7.4). High-resolution structures of -bound proteins provide little insight into this disparity, prompting structural analysis apo-proteins. A recent rat b-PV suggested that removal provokes substantial conformational changes—reorientation C, D, E helices; reorganization hydrophobic core; reduced interdomain contact; remodeling AB domain. The energetic penalty attendant to reversing these changes, it was suggested, could contribute attenuated ion-binding signature protein. That hypothesis is supported data presented herein, describing solution structure peptide backbone dynamics -free a-PV. marked contrast b-PV, apo- -loaded forms are quite similar. Significant differences appear be confined loop regions molecule. This finding implies a-PV enjoys elevated affinity because metal ionbinding events do not require major rearrangement concomitant sacrifice energy.