Title: Active Form of Neuroprotective Humanin, HN, and Inactive Analog, S7AHN, are Monomeric and Disordered in Aqueous Phosphate Solution at pH 6.0; No Correlation of Solution Structure with Activity
VOLUME: 16 ISSUE: 2
Author(s):Fumio Arisaka, Tsutomu Arakawa, Takako Niikura and Yoshiko Kita
Affiliation:Alliance Protein Laboratories, 3957 Corte Cancion, Thousand Oaks, CA 91360, USA.
Keywords:Humanin, Neuroprotection, aggregation, disordered structure, inactive humanin
Abstract: A novel neuroprotective peptide, Humanin (HN), has a strong tendency to aggregate in phosphate-buffered saline. Here we attempted to reduce aggregation employing an aqueous phosphate solution, without NaCl, at pH 6.0 and low peptide concentrations wherever possible. Such a condition, though not fully physiological, allowed us to determine the secondary structure and molecular weight of the peptides. Comparison of a parent HN peptide, an inactive analog (S7AHN) and a 1000-fold more active analog (S14G-HN) showed no apparent differences in the secondary structure. These peptides were all disordered over the wide range of peptide concentration. Sedimentation analysis was done only for HN and S7A-HN and showed aggregation into soluble oligomers in 20 mM phosphate at pH 6.0. Aggregation was greatly suppressed in 5 mM phosphate at the same pH in terms of aggregate size, with the formation of smaller oligomers. Sedimentation velocity experiments at 60,000 rpm in 5 mM phosphate at pH 6.0 showed that both HN and S7A-HN distributed into soluble aggregates that sedimented to the bottom of the cell and low molecular weight species that approached sedimentation equilibrium. The mass of this low molecular weight species was determined by sedimentation equilibrium to be close to monomers for both peptides. Thus, these results clearly demonstrate that the active HN and inactive S7AHN are identical in structure and hence there is no apparent correlation between solution structure and biological activity.
