Journal of Neuroscience, Vol 10, 1838-1846, Copyright © 1990 by Society for Neuroscience
Identification of serine 473 as a major phosphorylation site in the neurofilament polypeptide NF-L
ZS Xu, WS Liu and M Willard
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Neurofilaments are composed of 3 polypeptides designated NF-H, NF-M, and
NF-L, all of which are subject to posttranslational phosphorylation. It has
been suggested that phosphorylation of the NF-L polypeptide can influence
the assembly of NF-L into filaments, but the sites at which NF-L is
phosphorylated are unknown. To locate these phosphorylation sites, we have
identified phosphopeptides of NF-L by labeling them with 32P both in vitro
and in cultured neurons and also by observing their change in
chromatographic behavior after they have been treated with phosphatase. We
report here that serine 473, in the carboxy-terminal tail domain of NF-L,
is a major substrate in vitro for protein kinases endogenous to a crude
cytoskeleton-containing fraction. Moreover, serine 473 is a major
phosphorylation site in vivo; in neurofilaments isolated from rat spinal
cord, approximately 73% of serine 473 was phosphorylated, and accounted for
at least one-third of the total phosphate associated with NF-L. The
identification of this phosphorylation site in NF-L provides a criterion
for identifying the protein kinase that phosphorylates NF-L and raises the
question of its function.