Biophysical and structural studies of the human calcium- and integrin-binding protein family: understanding their functional similarities and differences.
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 αIIb cytoplasmic domain and the integrin α7b membrane-proximal fragment. Fluorescence experiments using a 7-azatryptophan labeled peptide demonstrate that CIB2, CIB3, and CIB4 are binding partners for the integrin αIIb subunit, which suggests that they are potentially involved in regulating integrin αIIb subunit activation. The distinct responses of αIIb 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.
Biochemistry Research Group, Department of Biological Sciences, University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada.
Hao
H
Huang
Joel N
JN
Bogstie
Hans J
HJ
Vogel
D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship
C109198:CIB1 protein, human; C577150:CIB2 protein, human; C577151:CIB3 protein, human; C577152:CIB4 protein, human; D002135:Calcium-Binding Proteins; D002118:Calcium