Biophysical and structural studies of the human calcium- and integrin-binding protein family: understanding their functional similarities and differences.
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Huang H, Bogstie JN, Vogel HJ
Biophysical and structural studies of the human calcium- and integrin-binding protein family: understanding their functional similarities and differences.
Biochem Cell Biol. 2012 Oct;90(5):646-56. doi: 10.1139/o2012-021. Epub 2012 Jul 11.
- PubMed ID
- 22779914 [ View in PubMed]
- Abstract
The human calcium- and integrin-binding protein 1 (CIB1) plays important roles in various cellular functions. In this study, three other members of this protein family (CIB2-4: CIB2, CIB3, and CIB4) were purified and subsequently characterized using biophysical and structural approaches. As expected from sequence alignments, CIB2-4 were shown to bind calcium (Ca(2+)) and magnesium (Mg(2+)) ions. Binding of Ca(2+) or Mg(2+) ions changes the secondary structure of CIB2-4 and the exposure of hydrophobic surface area. Ca(2+) and Mg(2+) ions also stabilize the tertiary structures for CIB2 and CIB3. Through in vitro binding experiments, we show that CIB2 can interact with the integrin alphaIIb cytoplasmic domain and the integrin alpha7b membrane-proximal fragment. Fluorescence experiments using a 7-azatryptophan labeled peptide demonstrate that CIB2, CIB3, and CIB4 are binding partners for the integrin alphaIIb subunit, which suggests that they are potentially involved in regulating integrin alphaIIb subunit activation. The distinct responses of alphaIIb to the different CIB3 and CIB4 metal (Ca(2+) and Mg(2+)) binding states imply a potential connection between the calcium and integrin signaling pathways.