Role of the helical domain in fatty acid transfer from adipocyte and heart fatty acid-binding proteins to membranes: analysis of chimeric proteins.
The adipocyte and heart fatty acid-binding proteins (A- and HFABP) are members of a lipid-binding protein family with a beta-barrel body capped by a small helix-turn-helix motif. Both proteins are hypothesized to transport fatty acid (FA) to phospholipid membranes through a collisional process. Previously, we suggested that the helical domain is particularly important for the electrostatic interactions involved in this transfer mechanism (Herr, F. M., Aronson, J., and Storch, J. (1996) Biochemistry 35, 1296-1303; and Liou, H.-L., and Storch, J. (2001) Biochemistry 40, 6475-6485). Despite their using qualitatively similar FA transfer mechanisms, differences in absolute transfer rates as well as regulation of transfer from AFABP versus HFABP, prompted us to consider the structural determinants that underlie these functional disparities. To determine the specific elements underlying the functional differences between AFABP and HFABP in FA transfer, two pairs of chimeric proteins were generated. The first and second pairs had the entire helical domain and the first alpha-helix exchanged between A- and HFABP, respectively. The transfer rates of anthroyloxy-labeled fatty acid from proteins to small unilamellar vesicles were compared with the wild type AFABP and HFABP. The results suggest that the alphaII-helix is important in determining the absolute FA transfer rates. Furthermore, the alphaI-helix appears to be particularly important in regulating protein sensitivity to the negative charge of membranes. The alphaI-helix of HFABP and the alphaII-helix of AFABP increased the sensitivity to anionic vesicles; the alphaI-helix of AFABP and alphaII-helix of HFABP decreased the sensitivity. The differential sensitivities to negative charge, as well as differential absolute rates of FA transfer, may help these two proteins to function uniquely in their respective cell types.
Liou
Heng-Ling
HL
Department of Nutritional Sciences, and the Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, New Jersey 08901-8525, USA.
Kahn
Peter C
PC
Storch
Judith
J
D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005227:Fatty Acids / Q000378:metabolism*; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009206:Myocardium / Q000378:metabolism*; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins
D002352:Carrier Proteins; D017931:DNA Primers; C107608:FABP7 protein, human; C082667:Fabp5 protein, mouse; C086936:Fabp7 protein, mouse; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005227:Fatty Acids; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D011993:Recombinant Fusion Proteins; D025521:Tumor Suppressor Proteins