Humanin Structural Versatility and Interaction with Model Cerebral Cortex Membranes

Abstract

Humanin (HN) is a recently identified neuroprotective peptide able to inhibit neurotoxicity induced by various insults which can be related to Alzheimer disease (AD) as well as to cell death induced by other stimuli. Previous CD and NMR studies demonstrated that HN adopts an unordered conformation in water, a alpha-helix conformation in 30% TFE, and a beta-sheet structure in PBS. Furthermore, other studies clearly indicated HN as a secreted peptide, able to prevent neuronal cell death caused by amyloid beta (Abeta) derivatives. Although Abeta was found to interact with neuronal membranes, currently there is not experimental evidence unveiling HN interaction with membranes. In this paper a spin labeling technique coupled with electron paramagnetic resonance (EPR) and circular dichroism (CD) has been used to study the structure and dynamics of HN in solution and for the first time in the presence of model cerebral cortex membranes (CCM). We have demonstrated that HN has a great tendency to aggregate even at low concentrations in water solutions at different ionic strengths and monomerizes in the TFE apolar environment. We also showed that HN slightly perturbs model CCM at the surface assuming a clear beta-sheet conformation. In addition, HN increases the fluidity of the bilayer core without penetrating into the membrane.

Structure of three Humanin peptides with different activities upon interaction with liposome

“…The spectrum, i.e., a negative descending signal with decreasing wavelength, is essentially characterized as disordered, consistent with the previous data [24]. It has been observed that as the protein concentration was increased, the temperature was raised, or the ionic strength was increased, the HN tends to aggregate and undergo conformational changes [24,28,32]. Thus, the structure analysis was done primarily at 25 • C with 0.1 mg/ml in 10 mM phosphate, pH 7.0, except otherwise indicated.…”

“…A similar structure transition was also shown in the presence of model cerebral cortex membranes [32]. These results suggest that such a structure change may be prerequisite for the HN to exert neuroprotective activities.…”

“…Mutational analysis generated an essentially inactive analog with an S7A mutation and a highly active analog, S14G-HN, effective at nM range [5,9]. We have observed that these peptides are all disordered and monomeric at low peptide concentration in buffer solution and have tendency to aggregate at higher concentration, particularly in the presence of salts and at elevated temperature [15,23,24,28,32]. This means that the different activity is not simply due to the structure difference in aqueous solution.…”

d-Ser-containing humanin shows promotion of fibril formation

“…Substitution of Gly for Ser 14 (S14G-HN; HNG) dramatically increases the neuroprotective effect to the same level as that of [DSer 14 ]HN, whereas substitution of Ala for Cys8 (C8A-HN; HNA) abolishes the effect because the molecule can no longer self-dimerize (Hashimoto et al 2001c;Terashita et al 2003). Recently, several groups elucidated the structural features of HN, HNG, and HNA under various conditions (Arakawa et al 2006;Arisaka et al 2008;Benaki et al 2005Benaki et al , 2006Pistolesi et al 2009). However, the structural characteristics of D-Ser-containing HNs, such as [D-Ser 7 ]HN, ] HN,14 ]HN, have not been defined.…”

The Neurovascular Protective Effect of S14G‐Humanin in a Murine MCAO Model and Brain Endothelial Cells

“…It should be noticed that there is a hydrophobic core region “GFSCLLLLTSEID” within the humanin sequence . Humanin can bind hydrophobic pockets of proteins as an α‐helical monomer . It is speculated that HNG might cross the BBB through transporters or humanin receptors on the surface of endothelial cells.…”