SV2A and SV2C contain a unique synaptotagmin-binding site

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Synaptic Vesicle Protein 2 (SV2) is crucial for calcium-evoked neurosecretion in neurons and endocrine cells.
• Mammals possess three SV2 genes: SV2A, SV2B, and SV2C.
• SV2A is known to interact with synaptotagmin, the primary candidate for the calcium sensor in exocytosis.

Purpose of the Study:

• To investigate the binding interactions between all SV2 isoforms and synaptotagmin.
• To determine the role of calcium in modulating these interactions.
• To elucidate the functional differences between SV2 isoforms, particularly SV2A, SV2B, and SV2C.

Main Methods:

• Investigated binding of native SV2 isoforms to synaptotagmin.
• Utilized isolated amino termini of SV2A and SV2C to study specific binding sites.
• Mapped the synaptotagmin-binding site to the N-terminal 57 amino acids of SV2A.
• Assessed the impact of SV2 amino termini on neurotransmission in cultured neurons.

Main Results:

• All native SV2 isoforms bind synaptotagmin via a common calcium-inhibited site.
• The amino termini of SV2A and SV2C exhibit an additional calcium-stimulated synaptotagmin-binding site.
• Removal of the SV2A N-terminal domain altered calcium-mediated inhibition of synaptotagmin binding.
• Expression of SV2A or SV2C amino termini inhibited neurotransmission, unlike SV2B.

Conclusions:

• The SV2-synaptotagmin interaction is integral to regulated exocytosis.
• SV2A and SV2C possess a distinct calcium-stimulated binding site, differentiating their function from SV2B.
• These findings highlight isoform-specific roles for SV2 proteins in synaptic transmission.