Calcium-binding lens membrane proteins

✍ Scribed by A. J. M. Den Eijnden-Van Raaij; A. L. M. Leeuw; R. M. Broekhuyse

• Book ID: 104639695
• Publisher: Springer-Verlag
• Year: 1986
• Tongue: English
• Weight: 854 KB
• Volume: 61
• Category: Article
• ISSN: 0012-4486
• DOI: 10.1007/bf00142351

✦ Synopsis

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 calmodufin. The EEP proteins contain calciumbinding sites with a total capacity of 25 tool Ca 2 § per mol protein. This high calcinmbinding capacity of EEP points to a function of these proteins as intracellnlar 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 calciumdependent 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, cahnodulin, 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 caimodulin. 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 caicium-independent manner. Via cahnodulin the junctions become calcium-sensitive.