TY  - JOUR
AU  - Haber-Pohlmeier, S.
AU  - Abarca Heidemann, K.
AU  - Körschen, H. G.
AU  - Kaur Dhiman, H.
AU  - Heberle, J.
AU  - Schwalbe, H.
AU  - Klein-Seetharaman, J.
AU  - Kaupp, U. B.
AU  - Pohlmeier, A.
TI  - Binding of Ca2+ to glutamic acid-rich polypeptides from the rod outer segment
JO  - Biophysical journal
VL  - 92
SN  - 0006-3495
CY  - New York, NY
PB  - Rockefeller Univ. Press
M1  - PreJuSER-56497
SP  - 3207 - 3214
PY  - 2007
N1  - Record converted from VDB: 12.11.2012
AB  - Rod photoreceptors contain three different glutamic acid-rich proteins (GARPs) that have been proposed to control the propagation of Ca(2+) from the site of its entry at the cyclic nucleotide-gated channel to the cytosol of the outer segment. We tested this hypothesis by measuring the binding of Ca(2+) to the following five constructs related to GARPs of rod photoreceptors: a 32-mer peptide containing 22 carboxylate groups, polyglutamic acid, a recombinant segment comprising 73 carboxylate groups (GLU), GARP1, and GARP2. Ca(2+) binding was investigated by means of a Ca(2+)-sensitive electrode. In all cases, Ca(2+) binds with low affinity; the half-maximum binding constant K(1/2) ranges from 6 to 16 mM. The binding stoichiometry between Ca(2+) ions and carboxylic groups is approximately 1:1; an exception is GARP2, where a binding stoichiometry of approximately 1:2 was found. Hydrodynamic radii of 1.6, 2.8, 3.3, 5.7, and 6.7 nm were determined by dynamic light scattering for the 32-mer, polyglutamic acid, GLU, GARP2, and GARP1 constructs, respectively. These results suggest that the peptides as well as GARP1 and GARP2 do not adopt compact globular structures. We conclude that the structures should be regarded as loose coils with low-affinity, high-capacity Ca(2+) binding.
KW  - Binding Sites
KW  - Calcium: chemistry
KW  - Glutamic Acid: chemistry
KW  - Nerve Tissue Proteins: chemistry
KW  - Peptides: chemistry
KW  - Protein Binding
KW  - Retinal Rod Photoreceptor Cells: chemistry
KW  - Nerve Tissue Proteins (NLM Chemicals)
KW  - Peptides (NLM Chemicals)
KW  - Glutamic Acid (NLM Chemicals)
KW  - Calcium (NLM Chemicals)
KW  - J (WoSType)
LB  - PUB:(DE-HGF)16
C6  - pmid:17218469
C2  - pmc:PMC1852358
UR  - <Go to ISI:>//WOS:000245544100028
DO  - DOI:10.1529/biophysj.106.094847
UR  - https://juser.fz-juelich.de/record/56497
ER  -