Family members are characterized by common protein domains, and they are implicated in synaptogenesis and the modulation of neurotransmitter release, suggesting a potential role in several neuropsychiatric diseases.

This phosphoprotein is loosely associated with the vesicular membrance and is easily dissociated by treatment with a salt, versus a detergent being required for its removal from the membrane.

This aided in the early determination of its structure using collagenase, which was later confirmed by amino acid sequencing and modern techniques.

Cleavage of synapsin I by collagenase fragments the elongated C-terminal and leaves the globular N-terminal domain intact.

[10] Synapsin I is present in the nerve terminal of axons, specifically in the membranes of synaptic vesicles based on immunocytochemistry.

[16] The calcium ion, Ca2+, binds to calmodulin to form a calcium/calmodulin complex which then activates the calcium/calmodulin-dependent protein kinase, in turn triggering phosphorylation.

Since it is only present in the vesicles in the reserve pool, the non-phosphorylated form of Synapsin I is considered to be an inhibitory regulator of neurotransmission.

In 1977, this first synaptic phosphoprotein was also purified and first characterized by Tetsufumi Ueda at the same laboratory at Yale University under Paul Greengard.

The novel techniques used to discover Synapsin I, were a combination of SDS gel electrophoresis and autoradiography developed by Tetsufumi Ueda in Greengard’s laboratory, that significantly enhanced the way proteins activated by phosphorylation could be observed.

Hiroo Maeno, a lab colleague, assisted with the sample preparations and radio-labelling ATP with P-32 at the gamma phosphate.