PMID: 21388953
Huang H, Ishida H, Yamniuk AP, Vogel HJ
The solution structures of Ca2+- CIB1 and Mg2+-CIB1 and their interactions with the platelet integrin {alpha}IIb cytoplasmic domain.
J Biol Chem. 2011 Mar 9.
The Calcium and Integrin Binding protein 1 (CIB1) is a ubiquitous Ca(2+) binding protein and a specific binding partner for the platelet integrin alphaIIb cytoplasmic domain, which confers CIB1's key role in haemostasis. CIB1 is also known to be involved in apoptosis, embryogenesis and the DNA damage response. In this work, the solution structures of both Ca(2+)-CIB1 and Mg(2+)-CIB1 were determined using solution-state NMR spectroscopy. The methyl groups of Ile,Leu and Val were selectively protonated to compensate for the loss of protons due to deuteration. The solution structure of Ca(2+)-CIB1 possesses smaller opened EF-hands in its C-domain compared to available crystal structures. Ca(2+)-CIB1 and Mg(2+)-CIB1 have similar structures, but the N-lobe of Mg(2+)-CIB1 is slightly more opened than that of Ca(2+)-CIB1. Additional NMR experiments, such as chemical shift perturbation and methyl group solvent accessibility as measured by the surface probe TEMPOL were carried out to further characterize the structures of Ca(2+)-CIB1 and Mg(2+)-CIB1 as well as their interactions with the integrin alphaIIb cytoplasmic domain. NMR measurements of backbone amide proton slow motion (mus-ms) dynamics confirmed that the C-terminal helix of Ca(2+)-CIB1 is displaced upon alphaIIb binding. The EF-hand III of both Ca(2+)-CIB1 and Mg(2+)-CIB1 was identified to be directly involved in the interaction of CIB1 and alphaIIb. Together, these data illustrate that CIB1 behaves quite different from related EF-hand regulatory calcium-binding proteins, such as calmodulin or neuronal calcium sensor proteins.