A lens intercellular junction protein, MP26, is a phosphoprotein.

Area of Science:

• Biochemistry
• Cell Biology
• Ophthalmology

Background:

• The major intrinsic protein (MP26) is a key component of the bovine lens plasma membrane.
• MP26 is believed to form intercellular junctions, potentially acting as a lens gap junction protein.

Purpose of the Study:

• To investigate the phosphorylation of MP26 in bovine lens fiber cells.
• To determine the sites and regulatory mechanisms of MP26 phosphorylation.

Main Methods:

• In vivo labeling of fetal bovine lens fragments with [32P]orthophosphate.
• Membrane isolation, SDS-PAGE, and autoradiography to identify phosphorylated proteins.
• Protease digestion and 2D gel electrophoresis to map phosphorylation sites.
• Phosphoamino acid analysis and in vitro kinase assays.

Main Results:

• MP26 was identified as a phosphorylated protein (Mr 26,000) in lens membranes.
• Phosphorylation occurred primarily on serine residues (90-95%) and to a lesser extent on threonine (5-10%).
• MP26 phosphorylation was reduced by lowering intracellular calcium and stimulated by forskolin and cAMP.
• Phosphorylation was localized to the cytoplasmic side, near the COOH-terminus of MP26.

Conclusions:

• MP26 undergoes phosphorylation, suggesting a regulatory role in lens function.
• Calcium and cAMP signaling pathways influence MP26 phosphorylation.
• These findings support the role of MP26 in forming functional lens gap junctions.