Abstract
The rat heart contains an abundant cytosolic protein which binds long chain fatty acids. We have determined its primary structure by Edman degradation of peptides generated from chymotryptic, tryptic, and elastase digestions. This polypeptide (Mr = 14,992) contains 134 amino acids and has a blocked (acetylated) NH2 terminus. The sequence of rat heart fatty acid-binding protein (FABP) is remarkably similar to the murine adipocyte 422 protein and the P2 protein of peripheral nerve myelin. Computer-assisted alignment of heart FABP and 422 revealed that 82 of 132 comparable residues are identical (62%). There are 77 identities out of 131 possible matches between this protein and the human myelin P2 protein (59%). Similar comparisons demonstrate that heart FABP has significant homology to several other proteins which bind hydrophobic ligands. The rank of order of similarity to heart FABP is: 422 greater than myelin P2 greater than cellular retinoic acid-binding protein greater than cellular retinol-binding protein II greater than cellular retinol-binding protein greater than intestinal FABP greater than liver FABP. These eight sequences form a family of paralogous homologues. Heart FABP has a region of internal homology involving tandemly arrayed oligopeptides spanning residues 71-100 and 101-131. This feature is not found in the 422 and P2 sequences. The endogenous ligands bound by the 422, P2, and heart FABP sequences have not been defined. Interpretation of the biological significance of their structural similarities and differences will require information about their ligand specificities and affinities.
Highlights
Rat HeartFatty Acid-binding Protein Is Highly Homologous to the Murine Adipocyte422 Protein and theP2 Protein of Peripheral Nerve Myelin*
The rank of order of simiendogenous free fatty acids found associated with this protein (2, 5 )
A variety of metabolic studies suggests that both proteins participate in the uptake,intracellular transport, and/or metabolism of free fatty acids and theiracyl-CoA esters
Summary
-- IT""h-r-GlEu-L1y"s"""1-""R- sn-Phe-Val-Glcy-1Th"r" -Tcr~ p-" L" y" s" -L"e"" u" -V"" a" l-" F"l~-Ser-Lys-R~-PCh2e-~-sp--~~-- Tyr--Re~--Ly-s-S- er-L-~u-- Gl~- -~al- -G~r y- -----. Less sequence identity is present between rat heart and intestinal FABP (Fig. 7B) When these two polypeptides are aligned using the same break penalty as was used for the 422 and P2 alignments, 40 identities out of 128 possible matches were documented (31%).The same alignment parameters generated 38 identities out of only 106 possible matches between rat liver and heartFABP (data not shown). This qualitative statement is supported by RELATE comparisons of the NHz-terminal and COOH-terminal 67 residues of heart FABP and the intact422 and P2 polypeptides (Table 11).This is not the case when the NH2-.
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