Electrostatic interactions govern the colisional mechanism of fatty acid transfer from intestinal fatty acid binding protein to phospholipid membranes.

FRANCHINI, G. R., HSU, K. T., STORCH, J. AND CORSICO, B.

Angra dos Reis, Brasil

Congreso; First LAPS Meeting; 2004

LAPS

Intestinal fatty acid binding protein (IFABP) is a member of a lipid-binding protein family abundantly expressed in intestinal enterocytes. It is hypothesized that fatty acid binding proteins (FABPs) are important in intracellular transport of fatty acids (FA). Fatty acid transfer from IFABP to phospholipid membranes is proposed to occur during protein-membrane collisional interactions. We have shown that the transfer process is modulated by the characteristics of the membrane, in particular, it was shown that IFABP is highly sensitive to the presence of acidic phospholipids in the acceptor membrane, particularly cardiolipin (CL). It is hypothesized that the membrane acidic phospholipids may interact with basic residues on the surface of IFABP. In the present study we analyzed: 1) the influence of the acceptor vesicles charge density and composition, and 2) the importance of the proteins positive surface charge, by selective acetylation of the surface lysine residues; in the transfer process from IFABP. A fuorescence resonance energy transfer assay was used to examine the rate and mechanism of transfer of anthroyloxy-fatty acid analogues (AOFA) from the native and acetylated IFABPs to phospholipid membranes. The results showed a signicant increase of the absolute rate of FA transfer from native IFABP to vesicles with increasing charge density and bigger hydrophobic volume. Transfer rate from the acetylated protein to zwitterionic vesicles was directly dependent on SUVs concentration, the same as the native. An increase in the negative charge of the acceptor vesicles resulted in a marked increase in the transfer rate from native IFABP but did not increase the rate from the acetylated IFABP. Moreover, the direct dependence on the SUVs concentration observed for zwiterionic vesicles, seems to bee gradually lost as the net negative charge of the acceptor vesicles increases. Finally, the transfer rate from native IFABP to acidic membranes depended upon the ionic strength of the incubation buffer, whereas the acetylated protein was not affected. Collectively, these studies indicate that: 1) the charge density and acyl packing of acceptor vesicles modulated the transfer process from IFABP, and 2) the positively charged lysine residues on IFABP are important for the efective collisional transfer of FA between IFABP and phospholipid bilayers. Thus ionic interactions between IFABP and membranes may play a key role in intracellular FA trafficking.