Identification of the neurotrophic factor sequence of prosaposin.
Prosaposin, recently identified as a neurotrophic factor (1), is the precursor of saposins A, B, C, and D. The neurotrophic activity of prosaposin resides in the saposin C domain. We have pinpointed the active sequence to a linear 12-mer located in the NH2-terminal sequence of saposin C (LIDNNKTEKEIL). Nanomolar concentrations of a 22-mer peptide encompassing this region stimulated neurite outgrowth and choline acetyltransferase activity, and prevented cell death in neuroblastoma cells. In primary cerebellar granule cells, the 22-mer also stimulated neurite outgroth. Studies of the neuroblastoma line NS20Y using a radiolabeled 18-mer from the neurotrophic region identified a high-affinity (Kd = 70 pM) binding site indicative of receptor-ligand interaction. The 22-mer stimulated protein phosphorylation of several proteins, some of which were tyrosine-phosphorylated after brief exposure similar to saposin C. Circular dichroism studies demonstrated that the 22-mer was converted from a random to a helical structure by addition of ganglioside GM1. The results are consistent with receptor-ligand binding by the peptide initiating a signal transduction cascade and resulting in neuronal differentiation.
O'Brien
J S
JS
Department of Neurosciences, University of California-San Diego, School of Medicine, La Jolla 92093-0634, USA.
Carson
G S
GS
Seo
H C
HC
Hiraiwa
M
M
Weiler
S
S
Tomich
J M
JM
Barranger
J A
JA
Kahn
M
M
Azuma
N
N
Kishimoto
Y
Y
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D006023:Glycoproteins / Q000737:chemistry* / Q000502:physiology; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009414:Nerve Growth Factors / Q000737:chemistry* / Q000502:physiology; D011487:Protein Conformation; D011498:Protein Precursors / Q000737:chemistry* / Q000502:physiology; D051381:Rats; D049231:Saposins; D014407:Tumor Cells, Cultured
D006023:Glycoproteins; D009414:Nerve Growth Factors; C483345:PSAP protein, human; D011498:Protein Precursors; C483344:Psap protein, mouse; C483347:Psap protein, rat; D049231:Saposins