Journal of Neuroscience, Vol 11, 3412-3421, Copyright © 1991 by Society for Neuroscience
The major 35S-methionine-labeled rapidly transported protein (superprotein) is identical to SNAP-25, a protein of synaptic terminals
A Loewy, WS Liu, C Baitinger and MB Willard
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Superprotein is a rapidly axonally transported protein that is
conspicuously labeled with 35S-methionine supplied to the cell bodies of
retinal ganglion cells. Superprotein candidates are apparent among the
rapidly transported proteins of many neurons from the CNS and PNS,
including cranial, sympathetic, sensory, and motor neurons from mammals,
fish, and amphibians. To determine the identity of Superprotein, we
purified it from rabbit visual system and spinal cord and determined the
amino acid sequence of seven of its tryptic peptides. The sequence shows
that Superprotein is SNAP-25, a protein recently predicted from a cDNA
sequence; SNAP-25 has been reported to be concentrated in the synaptic
terminals of a selected population of CNS neurons. We measured the amount
of radioactivity associated with Superprotein in tissue containing axons
(optic tract) and synaptic terminals (superior collicules) of rabbit
retinal ganglion cells. Labeled Superprotein disappeared from the superior
colliculus more rapidly than another protein (synapsin I-like protein) that
is concentrated in synaptic terminals. These results serve to unite the
observations on the synthesis, distribution, metabolism, and axonal
transport of Superprotein with observations of SNAP-25 and its mRNA.