{PDOC00345}
{PS00415; SYNAPSIN_1}
{PS00416; SYNAPSIN_2}
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* Synapsins signatures *
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Synapsins [1,2] are neuronal phosphoproteins that coat synaptic vesicles, bind
to several elements of  the cytoskeleton (including actin filaments),  and are
believed to function in the regulation of neurotransmitter release.

The synapsin family currently includes  the highly related  synapsin I and II.
Both synapsins exists in  two  alternatively spliced variants: IA and IB;  IIA
and IIB, which only differ in their carboxy-termini. It also includes synapsin
III.

Structurally synapsin IA/IB consist of a small N-terminal domain  (referred to
as the 'A' domain) that contains a  serine residue which serves as an acceptor
site for phosphorylation by both cyclic AMP-dependent protein kinase and Ca2+,
calmodulin-dependent protein kinase I.  The 'A' domain is followed by a linker
domain ('B') of some 80 residues.  The third domain ('C'), which  contains 300
amino acids, is  implicated  in the binding to actin and to synaptic vesicles.
The fourth domain 'D' is proline-rich and contains about 250 residues. Finally
the C-terminal spliced  domain  is known as 'E' (in IA), or 'F' (in IB).   The
structure of synapsin IIA/IIB also consists of  the 'A', 'B', and 'C' domains,
the 'D' domain is replaced by smaller  proline-rich region ('G'). Synapsin IIB
ends  with a small domain ('I'),  while the  larger C-terminal of synapsin IIA
consist of two  domains: 'H'  and 'E' (homologous to the 'E' of IA). A diagram
of the domains structure of the four synapsins is shown below.

 1        100       200       300       400       500       600       700
 |........|.........|.........|.........|.........|.........|.........|.
 +-+-------+------------------------------+------------------------+---+
 |A|   B   |               C              |              D         | E |  IA
 +-+-------+------------------------------+------------------------+---+

 +-+-------+------------------------------+------------------------+-+
 |A|   B   |               C              |              D         |F|    IB
 +-+-------+------------------------------+------------------------+-+

 +-+-------+------------------------------+---+-------+---+
 |A|   B   |               C              | G |   H   | E |               IIA
 +-+-------+------------------------------+---+-------+---+

 +-+-------+------------------------------+---+-+
 |A|   B   |               C              | G |I|                         IIB
 +-+-------+------------------------------+---+-+

We have  selected  two  conserved regions as signature patterns for synapsins.
The  first  one  is a conserved  octapeptide  in domain 'A' which contains the
phosphorylated  serine residue;    the  second  pattern  is a highly conserved
stretch of 11 residues located in the center of the 'C' domain.

-Consensus pattern: L-R-R-R-L-S-D-S
                    [The first S is phosphorylated]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Consensus pattern: G-H-A-H-[SA]-G-M-G-K-[IV]-K
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Last update: December 2001 / Patterns and text revised.

[ 1] Bahler M., Benfenati F., Valtorta F., Greengard P.
     "The synapsins and the regulation of synaptic function."
     BioEssays 12:259-263(1990).
     PubMed=2117454
[ 2] Kao H.T., Porton B., Hilfiker S., Stefani G., Pieribone V.A.,
     DeSalle R., Greengard P.
     "Molecular evolution of the synapsin gene family."
     J. Exp. Zool. 285:360-377(1999).
     PubMed=10578110; DOI=10.1002/(SICI)1097-010X(19991215)285:4<360::AID-JEZ4>3.0.CO;2-3

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