AJP - Cell Physiology, Vol 253, Issue 4 C500-C505, Copyright © 1987 by American Physiological Society
Structural and functional relationship of red blood cell protein 4.1 to synapsin I
K. E. Krebs, S. M. Prouty, I. S. Zagon and S. R. Goodman
Department of Physiology and Anatomy, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
It has been suggested that the neuron specific protein synapsin I is
closely related to red blood cell (rbc) protein 4.1. A systematic
comparison of the structural and functional properties of rbc protein 4.1
and synapsin I has been carried out. There is approximately a three order
of magnitude difference in cross reactivity of synapsin I with rbc 4.1
antiserum vs. synapsin I antiserum, as determined by a competitive
quantitative dot assay. Two-dimensional chymotryptic iodopeptide mapping
analysis demonstrated limited peptide homology (approximately 34% spot
overlap) between rbc 4.1 and synapsin I. Dephosphorylated synapsin I binds
saturably to brain spectrin (240/235) with an estimated dissociation
constant (Kd) of 700 nM and a maximal binding capacity of 4 mol synapsin
I/mol spectrin tetramer, similar to the affinity and stoichiometry of 4.1
binding to rbc spectrin. Synapsin I was found to bind to the terminal ends
of the brain spectrin tetramer by low-angle rotary shadowing, analogous to
4.1 binding to rbc spectrin. In summary, synapsin I is structurally and
immunologically distinct from rbc 4.1, yet shares functional similarities
with rbc 4.1 with respect to its spectrin binding characteristics.
