A conformational switch in the Piccolo C2A domain regulated by alternative splicing

Area of Science:

• Molecular Biology
• Structural Biology
• Neuroscience

Background:

• C2 domains are common calcium-binding protein modules.
• The active zone protein Piccolo (Aczonin) has a unique C2A domain with low calcium affinity, calcium-induced conformational changes, and calcium-dependent dimerization.

Purpose of the Study:

• To investigate the functional and structural impact of alternative splicing on the Piccolo C2A domain.
• To elucidate the mechanism by which a short alternatively spliced sequence alters C2 domain properties.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to determine the structure of the calcium-free long variant.
• Biochemical assays to assess calcium affinity, conformational changes, and dimerization of different splice forms.

Main Results:

• Removal of a nine-residue sequence via alternative splicing significantly increases calcium affinity.
• The spliced variant abolishes calcium-induced conformational changes and dimerization.
• NMR structure reveals the nine-residue sequence forms a beta-strand, blocking a calcium-binding site and requiring significant structural rearrangement for calcium binding in the long variant.

Conclusions:

• Alternative splicing provides a novel mechanism to regulate C2 domain function.
• The nine-residue sequence acts as a switch, controlling calcium sensitivity and protein interactions.
• This study uncovers a structural principle for modulating protein function through short alternatively spliced sequences.