PCLO (piccolo, also known as aczonin) is a large (more than 400 kDa) multidomain protein of the presynaptic cytomatrix in neurons, that is present in all vertebrate synapses, but is absent from invertebrates. It contains zinc finger and coiled-coil sequences, as well as N-terminal glutamine-rich sequence, and C-terminal PDZ domain followed by two C2 domains (C2A and C2B). In vitro binding and transfection experiments suggested that PCLO binds to multiple proteins including profilin and L-type calcium channels. It is involved in neurotransmitter release and insulin secretion.
