Cd2+ as a Ca2+ surrogate in protein-membrane interactions: isostructural but not isofunctional.
Due to its favorable spectroscopic properties, Cd(2+) is frequently used as a probe of Ca(2+) sites in proteins. We investigate the ability of Cd(2+) to act as a structural and functional surrogate of Ca(2+) in protein-membrane interactions. C2 domain from protein kinase Cα (C2α) was chosen as a paradigm for the Ca(2+)-dependent phosphatidylserine-binding peripheral membrane domains. We identified the Cd(2+)-binding sites of C2α using NMR spectroscopy, determined the 1.6 Å crystal structure of Cd(2+)-bound C2α, and characterized metal-ion-dependent interactions between C2α and phospholipid membranes using fluorescence spectroscopy and ultracentrifugation experiments. We show that Cd(2+) forms a tight complex with the membrane-binding loops of C2α but is unable to support its membrane-binding function. This is in sharp contrast with Pb(2+), which is almost as effective as Ca(2+) in driving the C2α-membrane association process. Our results provide the first direct evidence for the specific role of divalent metal ions in mediating protein-membrane interactions, have important implications for metal substitution studies in proteins, and illustrate the potential diversity of functional responses caused by toxic metal ions.
Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843, United States.
Krystal A
KA
Morales
Yuan
Y
Yang
Zheng
Z
Long
Pingwei
P
Li
Alexander B
AB
Taylor
P John
PJ
Hart
Tatyana I
TI
Igumenova
D002104:Cadmium / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D008958:Models, Molecular; D010743:Phospholipids / Q000737:chemistry*; D051571:Protein Kinase C-alpha / Q000737:chemistry* / Q000378:metabolism
D010743:Phospholipids; D002104:Cadmium; D051571:Protein Kinase C-alpha; D002118:Calcium