Ca(2+)-binding proteins in rat synaptic fractions surveyed by the 45Ca2+ overlay method

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Calcium-binding proteins play crucial roles in neuronal function.
• Subcellular localization of these proteins is vital for understanding synaptic transmission.
• The postsynaptic density (PSD) is a critical structure for synaptic plasticity.

Purpose of the Study:

• To survey calcium-binding proteins in various subcellular fractions of rat brain.
• To identify and characterize calcium-binding proteins specifically within the PSD.
• To investigate the relationship between PSD-associated kinases and calcium-binding proteins.

Main Methods:

• Utilized the 45Ca2+ overlay method to detect calcium-binding proteins.
• Fractionated rat brain into synaptic, subsynaptic, and soluble components.
• Investigated protein phosphorylation using Ca2+/calmodulin-dependent protein kinase II.

Main Results:

• Identified tubulin (55 kDa) and calmodulin (19 kDa) as major calcium-binding proteins present in all fractions.
• Discovered unique 140 kDa calcium-binding proteins exclusively in the cerebral cortex PSD.
• Found that the 140 kDa proteins are substrates for PSD-associated Ca2+/calmodulin-dependent protein kinase II.
• Suggested a potential identification of a 16 kDa protein as the beta-subunit of calcineurin.
• Detected calretinin and calbindin-D28k in soluble fractions of both cerebral cortex and cerebellum.

Conclusions:

• The cerebral cortex PSD contains distinct calcium-binding proteins not found elsewhere.
• Tubulin and calmodulin are ubiquitous calcium-binding proteins in rat brain subcellular fractions.
• The 140 kDa PSD proteins are involved in calcium signaling pathways.
• Further characterization of these unique PSD proteins is warranted.