Calcium-binding lens membrane proteins

Calcium-binding membrane-bound proteins are present in the vertebrate eye lens. Among these proteins are a distinct group of immunologically related extrinsic EDTA-extractable proteins (EEP) and calmodulin. The EEP proteins contain calcium-binding sites with a total capacity of 25 mol Ca2+ per mol p...

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Bibliographic Details
Published in:Documenta ophthalmologica 1986-01, Vol.61 (3-4), p.255-265
Main Authors: VAN DEN EIJNDEN-VAN RAAIJ, A. J. M, DE LEEUW, A. L. M, BROEKHUYSE, R. M
Format: Article
Language:English
Subjects:
Analytical, structural and metabolic biochemistry
Animals
Binding and carrier proteins
Biological and medical sciences
Calcium-Binding Proteins - metabolism
Calmodulin - metabolism
Cattle
Crystallins - metabolism
Eye Proteins - metabolism
Fundamental and applied biological sciences. Psychology
Intercellular Junctions - metabolism
Membrane Proteins - metabolism
Permeability
Proteins
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Summary:Calcium-binding membrane-bound proteins are present in the vertebrate eye lens. Among these proteins are a distinct group of immunologically related extrinsic EDTA-extractable proteins (EEP) and calmodulin. The EEP proteins contain calcium-binding sites with a total capacity of 25 mol Ca2+ per mol protein. This high calcium-binding capacity of EEP points to a function of these proteins as intracellular calcium store in the lens. However, EEP undergoes a conformational change upon calcium binding, indicating that these proteins may be involved in the regulation of calcium-dependent cellular processes in the lens. One of these processes is the action of communicating lens fiber junctions, which contain EEP as a main protein component. In addition to EEP, another calcium-binding protein in lens, calmodulin, probably functions as mediator of calcium in the regulation of the structure and function of lens junctions. Like other vertebrate calmodulins, lens calmodulin shows a calcium-dependent mobility shift on SDS-polyacrylamide gels and forms immune complexes with antiserum raised against vertebrate calmodulin. Lens calmodulin binds to the junction proteins MIP (main intrinsic protein, MW 26 Kdalton) and a 17.5 Kdalton polypeptide of lens fiber cells in a calcium-independent manner. Via calmodulin the junctions become calcium-sensitive.
ISSN:0012-4486
1573-2622
DOI:10.1007/BF00142351