Annexin VI binds to a synaptic vesicle protein, synapsin I

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Annexins are calcium-dependent phospholipid-binding proteins.
• Annexin VI has diverse cellular roles.
• Synapsin I is a key synaptic vesicle protein involved in neurotransmission.

Purpose of the Study:

• To identify proteins that bind Annexin VI in rat forebrain.
• To characterize the interaction between Annexin VI and synapsin I.
• To investigate the effect of synapsin I phosphorylation on Annexin VI binding.

Main Methods:

• Protein binding assays using rat forebrain homogenates and subcellular fractions.
• Western blotting and SDS-PAGE to identify Annexin VI-binding proteins.
• Biochemical characterization of Annexin VI-synapsin I interaction, including affinity measurements.
• In vitro phosphorylation of synapsin I and assessment of its effect on Annexin VI binding.

Main Results:

• Annexin VI bound to over 14 proteins in rat forebrain homogenates in a Ca2+/phospholipid-dependent manner.
• Synapsin I, identified as an 80,000 M(r) doublet, was enriched in purified synaptic vesicles and bound to Annexin VI.
• Annexin VI bound to the head domain of synapsin I with high affinity (KCa = 12.6 microM, KD = 270 nM).
• Phosphorylation of synapsin I by cAMP-dependent protein kinase and Ca2+/calmodulin-dependent protein kinase II inhibited Annexin VI binding in a kinase-specific manner.

Conclusions:

• Annexin VI is a multifunctional protein in the rat forebrain, interacting with various proteins including synapsin I.
• Annexin VI may regulate synapsin I function through Ca2+- and phospholipid-dependent binding.
• Synapsin I phosphorylation alters its interaction with Annexin VI, suggesting a regulatory mechanism for synaptic function.