Influence of monovalent cation identity on parvalbumin divalent ion-binding properties.
Rat alpha- and beta-parvalbumins have distinct monovalent cation-binding properties [Henzl et al. (2000) Biochemistry 39, 5859-5867]. Beta binds two Na(+) or one K(+), and alpha binds one Na(+) and no K(+). Ca(2+) abolishes these binding events, suggesting that the monovalent ions occupy the EF-hand motifs. This study compares alpha and beta divalent ion affinities in Na(+) and K(+) solutions. Solvent cation identity seriously affects alpha. In Hepes-buffered NaCl, at 5 degrees C, the macroscopic Ca(2+)-binding constants are 2.6 x 10(8) and 6.4 x 10(7) M(-1) and the Mg(2+) constants, 1.8 x 10(4) and 4.3 x 10(3) M(-1). In Hepes-buffered KCl, the Ca(2+) values increase to 2.9 x 10(9) and 6.6 x 10(8) M(-1) and the Mg(2+) values to 2.2 x 10(5) and 3.7 x 10(4) M(-1). Monte Carlo simulation of alpha binding data-employing site-specific constants and explicitly considering Na(+) binding-yields a K(Na) of 630 M(-1) and indicates that divalent ion-binding is positively cooperative. NMR data suggest that the lone Na(+) ion occupies the CD loop. Solvent cation identity has a smaller impact on beta. In Na(+), the Ca(2+) constants for the EF and CD sites are 2.3 x 10(7) and 1.5 x 10(6) M(-1), respectively; the Mg(2+) constants are 9.2 x 10(3) and 1.7 x 10(2) M(-1). In K(+), these values shift to 3.1 x 10(7) and 3.8 x 10(6) M(-1) and the latter to 1.4 x 10(4) and 2.9 x 10(2) M(-1). These data suggest that parvalbumin divalent ion affinity, particularly that of rat alpha, can be significantly attenuated by increased intracellular Na(+) levels.
Henzl
Michael T
MT
Department of Biochemistry, University of Missouri-Columbia, Columbia, Missouri 65211, USA. henzlm@missouri.edu
Larson
John D
JD
Agah
Sayeh
S
D000818:Animals; D002132:Calcium Radioisotopes / Q000737:chemistry; D002135:Calcium-Binding Proteins / Q000737:chemistry; D002151:Calorimetry; D002413:Cations, Divalent / Q000737:chemistry; D002414:Cations, Monovalent / Q000737:chemistry; D003956:Dialysis; D020832:EF Hand Motifs; D008274:Magnesium / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010320:Parvalbumins / Q000737:chemistry*; D011188:Potassium / Q000737:chemistry; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry; D051381:Rats; D012964:Sodium / Q000737:chemistry; D012996:Solutions
D002132:Calcium Radioisotopes; D002135:Calcium-Binding Proteins; D002413:Cations, Divalent; D002414:Cations, Monovalent; D010320:Parvalbumins; D020033:Protein Isoforms; D012996:Solutions; D012964:Sodium; D008274:Magnesium; D011188:Potassium