1. Biochim Biophys Acta. 2010 Nov;1798(11):2102-13. Epub 2010 Jul 13.

Acylated and unacylated ghrelin binding to membranes and to ghrelin receptor:
towards a better understanding of the underlying mechanisms.

Staes E, Absil PA, Lins L, Brasseur R, Deleu M, Lecouturier N, Fievez V, Rieux A,
Mingeot-Leclercq MP, Raussens V, Préat V.

Université catholique de Louvain, Unité de Pharmacie Galénique, 1200 Brussels,
Belgium. edith.staes@gmail.com

The O-octanoylation of human ghrelin is a natural post-translational modification
that enhances its binding to model membranes and could potentially play a central
role in ghrelin biological activities. Here, we aimed to clarify the mechanisms
that drive ghrelin to the membrane and hence to its receptor that mediates most
of its endocrinological effects. As the acylation enhances ghrelin lipophilicity 
and that ghrelin contains many basic residues, we examined the electrostatic
attraction and/or hydrophobic interactions with membranes. Using various
liposomes and buffer conditions in binding, zeta potential and isothermal
titration calorimetry studies, we found that whereas acylated and unacylated
ghrelin were both electrostatically attracted towards the membrane, only acylated
ghrelin penetrated into the headgroup and the lipid backbone regions of
negatively charged membranes. The O-acylation induced a 120-fold increase in
ghrelin local concentration in the membrane. However, acylated ghrelin did not
deeply penetrate the membrane nor did it perturb its organisation. Conformational
studies by circular dichroism and attenuated total reflection Fourier transformed
infrared as well as in silico modelling revealed that both forms of ghrelin
mainly adopted the same structure in aqueous, micellar and bilayer environments
even though acylated ghrelin structure is slightly more α-helical in a lipid
bilayer environment. Altogether our results suggest that membrane acts as a
"catalyst" in acylated ghrelin binding to the ghrelin receptor and hence could
explain why acylated and unacylated ghrelin are both full agonists of this
receptor but in the nanomolar and micromolar range, respectively.

PMID: 20637180 [PubMed - indexed for MEDLINE]