title: Complex regulation of voltage-dependent activation and inactivation properties of retinal voltage-gated Cav1.4 L-type Ca2+ channels by Ca2+-binding protein 4 (CaBP4).
abstract: Cav1.4 L-type Ca(2+) channels are crucial for synaptic transmission in retinal photoreceptors and bipolar neurons. Recent studies suggest that the activity of this channel is regulated by the Ca(2+)-binding protein 4 (CaBP4). In the present study, we explored this issue by examining functional effects of CaBP4 on heterologously expressed Cav1.4. We show that CaBP4 dramatically increases Cav1.4 channel availability. This effect crucially depends on the presence of the C-terminal ICDI (inhibitor of Ca(2+)-dependent inactivation) domain of Cav1.4 and is absent in a Cav1.4 mutant lacking the ICDI. Using FRET experiments, we demonstrate that CaBP4 interacts with the IQ motif of Cav1.4 and that it interferes with the binding of the ICDI domain. Based on these findings, we suggest that CaBP4 increases Cav1.4 channel availability by relieving the inhibitory effects of the ICDI domain on voltage-dependent Cav1.4 channel gating. We also functionally characterized two CaBP4 mutants that are associated with a congenital variant of human night blindness and other closely related nonstationary retinal diseases. Although both mutants interact with Cav1.4 channels, the functional effects of CaBP4 mutants are only partially preserved, leading to a reduction of Cav1.4 channel availability and loss of function. In conclusion, our study sheds new light on the functional interaction between CaBP4 and Cav1.4. Moreover, it provides insights into the mechanism by which CaBP4 mutants lead to loss of Cav1.4 function and to retinal disease.
authors.affiliation: Center for Integrated Protein Science CIPS-M, Department Pharmazie, Ludwig-Maximilians-Universität München, D-81377 München, Germany.
authors.forename: Lior
authors.initials: L
authors.lastname: Shaltiel
authors.forename: Christos
authors.initials: C
authors.lastname: Paparizos
authors.forename: Stefanie
authors.initials: S
authors.lastname: Fenske
authors.forename: Sami
authors.initials: S
authors.lastname: Hassan
authors.forename: Christian
authors.initials: C
authors.lastname: Gruner
authors.forename: Katrin
authors.initials: K
authors.lastname: Rötzer
authors.forename: Martin
authors.initials: M
authors.lastname: Biel
authors.forename: Christian A
authors.initials: CA
authors.lastname: Wahl-Schott
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009755:Night Blindness / Q000235:genetics / Q000378:metabolism / Q000401:mortality; D017434:Protein Structure, Tertiary; D012160:Retina / Q000378:metabolism* / Q000473:pathology; D012164:Retinal Diseases / Q000235:genetics / Q000378:metabolism / Q000473:pathology
chemical_list: C514441:CABP4 protein, human; C113330:CACNA1F protein, human; C494133:Cabp4 protein, mouse; C480684:Cacna1f protein, mouse; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002135:Calcium-Binding Proteins; D009419:Nerve Tissue Proteins