An unusual C(2)-domain in the active-zone protein piccolo: implications for Ca(2+) regulation of neurotransmitter release.
Ca(2+) regulation of neurotransmitter release is thought to require multiple Ca(2+) sensors with distinct affinities. However, no low-affinity Ca(2+) sensor has been identified at the synapse. We now show that piccolo/aczonin, a recently described active-zone protein with C-terminal C(2)A- and C(2)B-domains, constitutes a presynaptic low-affinity Ca(2+) sensor. Ca(2+) binds to piccolo by virtue of its C(2)A-domain via an unusual mechanism that involves a large conformational change. The distinct Ca(2+)-binding properties of the piccolo C(2)A- domain are mediated by an evolutionarily conserved sequence at the bottom of the C(2)A-domain, which may fold back towards the Ca(2+)-binding sites on the top. Point mutations in this bottom sequence inactivate it, transforming low-affinity Ca(2+) binding (100-200 microM in the presence of phospholipids) into high-affinity Ca(2+) binding (12-14 microM). The unusual Ca(2+)-binding mode of the piccolo C(2)A-domain reveals that C(2)-domains are mechanistically more versatile than previously envisaged. The low Ca(2+) affinity of the piccolo C(2)A-domain suggests that piccolo could function in short-term synaptic plasticity when Ca(2+) concentrations accumulate during repetitive stimulation.
Gerber
S H
SH
Center for Basic Neuroscience, Department of Molecular Genetics and Howard Hughes Medical Institute, UT Southwestern Medical Center, Dallas, TX 75390, USA.
Garcia
J
J
Rizo
J
J
Südhof
T C
TC
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D009479:Neuropeptides; D018377:Neurotransmitter Agents; C498630:PCLO protein, human; C498631:Pclo protein, mouse; C405514:Pclo protein, rat; D010743:Phospholipids; D002118:Calcium