The lipid acyl-chain dynamics in giant liposomes and characterization of domain 4 of the Wilson disease protein

Abstract

Steady-state and nanosecond time-resolved fluorescence of the nitro-2, 1, 3- benzoxadiazol-4-yl (NBD) probe and line tension force were determined in phospholipids acyl-chain dynamics in giant liposomes made from a homologous series of phosphatidylcholines (PC). The fluorescence spectroscopy of a NBD probe attached to the headgroup (NBD PE) or the tail (NBD PC) of the phospholipid were used to determine the rate of dithionite quenching in a homologous series of phospholipids. Similar experiments were performed in the gel and the fluid phases of the l,2-dimyristoyl-s«-glycero-3-phosphocholine (DMPC ). Nanosecond time scale lifetimes and anisotropy measurements were obtained by a 470 nm LED pulse laser diode and time correlated single photon counting detection.

The fluorescence lifetime and intensity of NBD PE and NBD PC in acyl-chain lengths from 12:0 PC to 20:0 PC were determined. The half life of dithionite quenching of NBD varied with both phospholipid chain length and the position of the fluorescent probes and of quenching in the gel, fluid and phase transition phases. Line tensions measured by laser ablation method in a homologous series of lipids, revealed acyl-chain length and phase state dependence.

Studies were conducted on human Wilson disease protein. This is a copper transporting ATPase found in the copper secretory pathway. It possesses six cytosolic metal binding domains in the N-terminus. These domains are involved in the acquisition of copper(I) from the metallochaperone HAH1. Insight into the stability of metal-binding domain four will be presented.