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Divalent ion‐binding properties of the two avian β‐parvalbumins
Author(s) -
Henzl Michael T.,
Agah Sayeh
Publication year - 2005
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.20701
Subject(s) - gene isoform , parvalbumin , divalent , chemistry , isothermal titration calorimetry , hepes , cooperative binding , binding site , crystallography , biochemistry , biology , organic chemistry , neuroscience , gene
Birds express three parvalbumins, one α isoform and two β isoforms. The latter are known as avian thymic hormone (ATH) and avian parvalbumin 3. Although both were discovered in thymus tissue, and presumably function in T‐cell maturation, they have been detected in other tissue settings. We have conducted detailed Ca 2+ ‐ and Mg 2+ ‐binding studies on recombinant ATH and the C72S variant of CPV3, employing global analysis of isothermal titration calorimetry data. In Hepes‐buffered saline, ATH binds Ca 2+ with apparent microscopic binding constants of 2.4 ± 0.2 × 10 8 and 1.0 ± 0.1 × 10 8 M −1 . The corresponding values for CPV3‐C72S are substantially lower, 4.5 ± 0.5 × 10 7 and 2.4 ± 0.2 × 10 7 M −1 , a 1.9‐kcal/mol difference in binding free energy. Thus, the β‐parvalbumin lineage displays a spectrum of Ca 2+ ‐binding affinity, with ATH and the mammalian β isoform at the high‐ and low‐affinity extremes and CPV3 in the middle. Interestingly, despite its decreased Ca 2+ affinity, CPV3‐C72S exhibits increased affinity for Mg 2+ , relative to ATH. Whereas the latter displays Mg 2+ ‐binding constants of 2.2 ± 0.2 × 10 4 and 1.2 ± 0.1 × 10 4 M −1 , CPV3‐C72S yields values of 5.0 ± 0.8 × 10 4 and 2.1 ± 0.3 × 10 4 M −1 . Proteins 2006. © 2005 Wiley‐Liss, Inc.