The glutamate-rich region of the larger lamprey neurofilament sidearm is essential for proper neurofilament architecture.

The carboxyl terminal "tail" domains of the heavy and middle molecular weight mammalian neurofilament (NF) proteins regulate inter-NF spacing and formation of organized networks. The C-terminal region of the larger of the two lamprey NF subunits (NF-180) resembles these mammalian proteins in that it consists of a proximal glutamate-rich region and a distal region containing multiple phosphorylation sites. To investigate the role of these two sidearm domains in the organization of lamprey NFs, we generated plasmids lacking the glutamate-rich domain, the domain containing multiple phosphorylation sites, or both, and examined the impact of the resultant mutant proteins on the endogenous NF network in differentiated NB21/d1 neuroblastoma cells. We present evidence that, like mammalian NFs, the glutamate-rich region of NF-180 sidearm plays a critical role in NF architecture.