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S.–E. Penney, P. Desmeules, C. Salesse; Calcium–and Integrin–Binding Protein (CIB) Is Expressed in Human Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1708.
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Purpose: CIB (calcium–and integrin–binding protein) is a 191 amino acids protein that shares properties with recoverin which is found in retinal rod cells from vertebrates. Being widely distributed in the human body, the functions of CIB are not well understood. CIB was first discovered for its interaction with integrin alphaIIb beta3. Like recoverin, CIB secondary structure comprises four EF–hands motifs and two of them are known to bind calcium in a sequential manner. The N–terminal of CIB is myristoylated in vivo. It has been suggested that CIB could a member of the calcium–myristoyl switch family of proteins which includes recoverin as the most studied member. The present study was performed to determine if CIB were expressed by human retina and to study its calcium–dependent interactions with lipids in order to assess its function. Methods: Immunofluorescence analyses by confocal microscopy of retina sections using a monoclonal antibody against CIB were performed to determine its cellular expression. CIB gene sequence has been amplified by RT–PCR using RNA extracted from human retina. The CIB gene was cloned in an expression vector and introduced in a E.coli host strain by transformation. After CIB overexpression, the protein was purified by a single–step chromatography. Surface pressure measurements at the air/water interface allowed to measure binding of CIB to phospholipid monolayers. Results: Immunofluorescence analyses have shown that CIB is expressed by human retina with particular reference for photoreceptors. Highly pure recombinant CIB has been obtained with high yield. Finally, we have found that CIB binds to phospholipid monolayers and that this binding was enhanced by calcium ions. Conclusions: We report for the first time the expression of CIB by photoreceptors and its binding to lipid monolayers in a calcium dependent manner.
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