title: Isoforms of rat liver fatty acid binding protein differ in structure and affinity for fatty acids and fatty acyl CoAs.
abstract: Although native rat liver fatty acid binding protein (L-FABP) is composed of isoforms differing in isoelectric point, their comparative structure and function are unknown. These properties of apo- and holo-L-FABP isoforms were resolved by circular dichroism, time-resolved fluorescence spectroscopy, and binding/displacement of fluorescent ligands. Both apo-isoforms had similar hydrodynamic radii of 18.5 A, but apo-isoform I had a greater alpha-helical content and exhibited a longer Tyr lifetime, indicative of secondary and tertiary structural differences from isoform II. Isoforms I and II both had two fatty acid or fatty acyl CoA binding sites. Ligand binding decreased the isoform hydrodynamic radii by 3-4 A and increased Tyr rotational motions in a more restricted range. Fatty acyl CoAs were more effective than fatty acids in altering the isoform structures. Scatchard analysis showed that both isoforms bound cis- parinaric acid with high affinity (Kd values 41 and 60 nM, respectively) and bound trans-parinaric acid with 2- and 7-fold, respectively, higher affinity than for cis-parinaric acid. In contrast, isoform I had higher affinity for cis- and trans-parinaroyl CoAs (Kd values of 33 and 14 nM) than did isoform II (Kd values of 110 and 97 nM), thereby resulting in biphasic plots of parinaroyl-CoA binding to native L-FABP. Finally, displacement studies indicated that each isoform displayed distinct specificities for fatty acid/fatty acyl CoA chain length and unsaturation. Thus, rat L-FABP isoforms differ markedly in both structure and ligand binding function.
authors.affiliation: Department of Physiology and Pharmacology, Texas A&M University, TVMC, College Station 77843-4466, USA.
authors.forename: A
authors.initials: A
authors.lastname: Frolov
authors.forename: T H
authors.initials: TH
authors.lastname: Cho
authors.forename: E J
authors.initials: EJ
authors.lastname: Murphy
authors.forename: F
authors.initials: F
authors.lastname: Schroeder
mesh_terms: D000214:Acyl Coenzyme A / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D002942:Circular Dichroism; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005227:Fatty Acids / Q000737:chemistry* / Q000378:metabolism; D005456:Fluorescent Dyes; D007536:Isomerism; D008099:Liver / Q000737:chemistry* / Q000201:enzymology; D018996:Myelin P2 Protein / Q000737:chemistry* / Q000378:metabolism; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D014443:Tyrosine
chemical_list: D000214:Acyl Coenzyme A; D002352:Carrier Proteins; C493320:Fabp1 protein, mouse; C493321:Fabp1 protein, rat; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005227:Fatty Acids; D005456:Fluorescent Dyes; D018996:Myelin P2 Protein; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; C086427:parinaroyl-coenzyme A; D014443:Tyrosine