Note. The novel nucleotide sequence data published here have been deposited with the EMBL, GenBank, and DDBJ sequence data banks and are available under accession number X86901.
Cloning, Expression and Characterization of Two Putative Calcium-binding Sites in Human Non-Erythroid α-Spectrin
Article first published online: 3 MAR 2005
European Journal of Biochemistry
Volume 230, Issue 2, pages 658–665, June 1995
How to Cite
Lundberg, S., Björk, J., Löfvenberg, L. and Backman, L. (1995), Cloning, Expression and Characterization of Two Putative Calcium-binding Sites in Human Non-Erythroid α-Spectrin. European Journal of Biochemistry, 230: 658–665. doi: 10.1111/j.1432-1033.1995.0658h.x
- Issue published online: 3 MAR 2005
- Article first published online: 3 MAR 2005
- (Received 6 March 1995) – EJB 95 0360/3
- calcium-binding protein
The C-terminus of α-spectrins contains two putative calcium-binding sites or EF-hands. To characterize the binding, we have isolated clones from a human fetal liver cDNA library and expressed several fragments comprising either one or both of these sites. When the isolated clones were sequenced, we found that three consecutive nucleotides differed compared to the published sequence. The discrepancy affected two codons in the first of the two putative calcium sites. These codons translated into glutamate and phenylalanine, which are identical to the residues present at the same position in other α-spectrins.
In the presence of magnesium, only recombinant peptides comprising the second putative site bound calcium as determined by a calcium overlay assay. Although the first putative EF-hand appeared to bind some calcium in the absence of magnesium, no binding could be detected under stringent conditions. Therefore, it is likely that the second EF-hand constitutes the only functional calcium-binding site in the C-terminus of human non-erythroid α-spectrin. Since peptides comprising the second EF-hand bound calcium nearly as well as intact spectrin, it is also apparent that the second EF-hand constitutes the major binding site for calcium in spectrin. The relative change in negative ellipticity, induced by the binding of calcium, indicates a dissociation constant of approximately 120 μM.