title: Calcium-dependent association of calmodulin with the C-terminal domain of the tetraspanin protein peripherin/rds.
abstract: Peripherin/rds (p/rds), an integral membrane protein from the transmembrane 4 (TMF4) superfamily, possesses a multi-functional C-terminal domain that plays crucial roles in rod outer segment (ROS) disk renewal and structure. Here, we report that the calcium binding protein calmodulin (CaM) binds to the C-terminal domain of p/rds. Fluorescence spectroscopy reveals Ca2+-dependent association of CaM with a polypeptide corresponding to the C-terminal domain of p/rds. The fluorescence anisotropy of the polypeptide upon CaM titration yields a dissociation constant (KD) of 320 +/- 150 nM. The results of the fluorescence experiments were confirmed by GST-pull down analyses in which a GST-p/rds C-terminal domain fusion protein was shown to pull down CaM in a calcium-dependent manner. Moreover, molecular modeling and sequence predictions suggest that the CaM binding domain resides in a p/rds functional hot spot, between residues E314 and G329. Predictions were confirmed by peptide competition studies and a GST-p/rds C-terminal domain construct in which the putative Ca2+/CaM binding site was scrambled. This GST-polypeptide did not associate with Ca2+/CaM. This putative calmodulin domain is highly conserved between human, mouse, rat, and bovine p/rds. Finally, the binding of Ca2+/CaM inhibited fusion between ROS disk and ROS plasma membranes as well as p/rds C-terminal-domain-induced fusion in model membrane studies. These results offer a new mechanism for the modulation of p/rds function.
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269, USA.
authors.forename: T C
authors.initials: TC
authors.lastname: Edrington
authors.forename: P L
authors.initials: PL
authors.lastname: Yeagle
authors.forename: Cheryl L
authors.initials: CL
authors.lastname: Gretzula
authors.forename: K
authors.initials: K
authors.lastname: Boesze-Battaglia
mesh_terms: D000818:Animals; D001923:Brain Chemistry; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002147:Calmodulin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D006801:Humans; D007381:Intermediate Filament Proteins / Q000737:chemistry / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008958:Models, Molecular; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D064531:Peripherins; D011485:Protein Binding / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000737:chemistry / Q000378:metabolism
chemical_list: D002147:Calmodulin; D007381:Intermediate Filament Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; C578994:PRPH protein, human; C578997:PRPH2 protein, human; D010455:Peptides; D064531:Peripherins; C578996:Prph2 protein, mouse; C579003:Prph2 protein, rat; D011993:Recombinant Fusion Proteins; D002118:Calcium