Activity-dependent neurotrophic factor (ADNF) is a glia-derived neurotrophic
peptide, which protects neurons from tetrodoxin treatment and
Alzheimer's disease-related and
amyotrophic-lateral-sclerosis-related insults at femto-molar concentrations. However, the mechanism of the femto-molar neuroprotection by the
peptide has not been elucidated. The characterization of the
peptide structure in
solution at molecular level should shed light in the mechanism of such extremely high
biological activity. From that point of view, the secondary and quaternary structure analysis of
ADNF9, an active
core fragment peptide of ADNF, was performed by circular dichroism (CD) and sedimentation equilibrium.
ADNF9 has also been shown to exhibit a neurotrophic activity in femto-molar concentrations; in this study it showed sub-pM neuroprotective activity against V642I-APP-induced cytotoxity in the mouse primary cortical neuron. CD analysis showed that the secondary structure of
ADNF9 is identical in water and
phosphate-buffered saline (PBS) and is independent of the
peptide concentration. The CD spectra appear to be characterized most likely as disordered. The sedimentation equilibrium experiments demonstrated monomeric structure of the
protein over the wide range of
peptide concentration. There is a slight enhancement of CD intensity at 37 degrees C relative to 20 degrees C, suggesting a possible hydrophobic association of the
peptide. There is no change in the secondary structure in PBS upon freeze-thaw treatment, which has previously been suggested to cause activity loss.