Tryptophan insertion mutagenesis of liver fatty acid-binding protein Acid-binding Protein

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Description/Abstract

Liver fatty acid-binding protein (FABP) binds a variety
of non-polar anionic ligands including fatty acids,
fatty acyl CoAs, and bile acids. Previously we prepared
charge reversal mutants and demonstrated the importance
of lysine residues within the portal region in ligand
and membrane binding. We have now prepared
several tryptophan-containing mutants within the portal
region, and one tryptophan at position 28 (L28W) has
proved remarkably effective as an intrinsic probe to
further study ligand binding. The fluorescence of the
L28W mutant was very sensitive to fatty acid and bile
acid binding where a large (up to 4-fold) fluorescence
enhancement was obtained. In contrast, the binding of
oleoyl CoA reduced tryptophan fluorescence. Positive
cooperativity for fatty acid binding was observed while
detailed information on the orientation of binding of
bile acid derivatives was obtained. The ability of bound
oleoyl CoA to reduce the fluorescence of L28W provided
an opportunity to demonstrate that fatty acyl CoAs can
compete with fatty acids for binding to liver FABP under
physiological conditions, further highlighting the
role of fatty acyl CoAs in modulating FABP function in
the cell.