Oral communication, CS2 / C6

Official XXIst International Pigment Cell Conference website - 21-24 Sept 2011, Bordeaux - France | updated: September 04 2011

Probing the Melanosome Surface using Molecular Rulers

SPEAKER K. Glass #whois submiter ?
AUTHOR(s) K. Glass, R. Rengifo, J.D. Simon

Little is known about the molecular organization of the melanosome surface. There are carboxylic acids present on the melanonsome surface, but the functional importance of these moieties – how they participate in binding of metal ions and transport into the melanosome interior – remains elusive. We have developed an approach for studying the distance between neighboring carboxylic acid groups, where we take advantage of the heat released upon ion pairing between carboxylate and ammonium groups. Specifically, the binding of diamines, which have expanding linear aliphatic carbon chain lengths separating the charged amine groups, are used as molecular rulers to gauge the distance between the carboxylic acid groups on the surface of sepia and choroid melanosomes using isothermal titration calorimetry (ITC). At pH 5.8, the carboxyl groups on the surface of the melanosome are deprotonated, and both amine groups on the diamines are protonated. ITC measurement of the equilibrium constants and capacity for binding as a function of the distance between the two amine groups provides a unique and novel insight into the distances between neighboring carboxylic acid sites on the melanosome surface. In the case of Sepia, the binding of +H3N-(CH2)m-NH3+ (m=1-4) exhibit binding constants of 1.89 x 10^3, 1.14 x 10^4, 1.71 x 10^3, and 7.79 x 10^2. The lowest energy conformation occurs when the two nitrogens of the diamines are 22.7, 37.8, 44.0, and 58.8 nm apart. These results suggest a narrow distribution of distances between nearest neighboring carboxylic acid groups, on the order of ~38 nm.



Advertisement from our sponsor:
Astellas Pharma Worldwide

Université de Bordeaux 2 & Conseil Régional Aquitaine