Protein-membrane interaction and ligand transfer to membranes from intestinal fatty acid binding proteins (FABPs) employing natural ligands

EDUARDO DE GERÓNIMO; LISANDRO FALOMIR.LOCKHART; MARÍA XIMENA GUERBI; DAVID C. WILTON; BETINA CÓRSICO

Turku

Congreso; 48th ICBL: 4 - 8 September 2007 - Turku, Finland; 2007

International Conference on the Bioscience of Lipids

Intestinal FABP (IFABP) belongs to a family of small cytosolic proteins involved in lipid transport and metabolism that share a common structure. IFABP structure consists of ten antiparallel β-strands that form a β-barrel, which is capped by two short α-helices arranged as a helix-turn-helix segment. Fatty acid transfer from IFABP to phospholipid membranes is proposed to occur during protein-membrane collisional interactions (while for LFABP transfer occurs by diffusion through the aqueous phase), in which ionic interactions between positively charged residues on the protein surface and negatively charged phospholipid headgroups are involved. We have also shown, using a helix-less variant of IFABP that the α-helical region of IFABP is involved in membrane interactions, and appears to play a primary role in the collisional mechanism of fatty acid transfer from IFABP to membranes. The objective of this study was to determine the membrane penetration depth of the IFABP portal region by fluorescence quenching techniques and analyze how it is affected by the charge of the membrane surface and by the ionic strength. We have engineered a series of IFABP single-tryptophan mutants in the portal region. The Trp fluorescence of these mutants is quenched by a series of [1- palmitoyl-2-(dibromostearoyl)phosphatidylcholine] (BrPC) large unilamellar vesicles with bromines at different positions along the fatty acid acyl chain. The results show clearly that the IFABP portal region is the membrane binding domain and is located within the lipid bilayer. Moreover, increasing the negative charge of the membrane could affect the depth and angle of insertion depth.