Initial studies of the cytoplasmic FABP superfamily

Abstract

Our colleagues and we have determined the complete primary structure of a low molecular weight cytoplasmic FABP (also known as z-protein) that binds to LCFAs with high affinities, obtained from rat liver. At the same time, we were the first to propose that rat FABP1, bovine FABP8 (MP-2), bovine CRBP and rat CRABP constituted a protein superfamily in 1982. Since then, extensive investigation of structures, functions and expressions has been carried out on a whole family of FABPs. Analyses of rat heart FABP; FABP1, FABP3 and alpha(2U)-globulin expressed in rat kidney; discovery of ileal FABP6 (I-15P); and first application of FABP2 as a diagnostic marker also stand out in particular.

Fig. 1

(A) The complete amino acid sequence of rat FABP1 (z-protein). CB, CNBr-fragments; T, Tryptic peptides; SP, Staphylococcal protease peptides; H, Hydroxylamine peptide. (→), Edman degradation; (←), Carboxypeptidase digestion. (B) Repetitive sequence in rat FABP1. Identical and conservative amino acids are respectively shown by asterisk (*) and dot (.).

Fig. 2

Comparison of rat FABP1 amino acid sequence to the complete bovine FABP8 (MP-2), the partial CRBP and CRBP sequences. FABP1, rat liver; FABP8, bovine peripheral nerve myelin; CRBP, bovine retina; CRABP, rat testis.

Fig. 3

Phylogenetic tree of cFABP superfamily. The bootstrap neighbor-joining phylogenetic tree was constructed using ClustalW2. The bootstrap values and each scale bar are not indicated just showing genetic tree outline.

Fig. 4

Sequence similarity of rat FABP6 (I-15P) and FABP1. Identical or functionally conserved amino acids, designated on the basis of chemical similarity and accepted point-mutation data, are enclosed in boxes.

Fig. 5

Human FABP6 promoter contains FXR responsive element. FXRE; farnesoid X-receptor responsive element, SRE; sterol regulatory element, BARE; bile acid responsive element.

Fig. 6

Comparison among healthy controls (normal; n = 35), patients with acute abdominal pain (abdominal pain; n = 48), patients with strangulation of the small bowel (BS; n = 8), and patients with mesenteric infarction (MI; n = 5). The dashed line indicates the tentative cutoff value (100 ng/mL) for serum FABP2 level in the EIA.