engleski

Exploring the role of amino acid-18 of the leucine binding proteins of E. coli

Two periplasmic binding proteins of E. coli, the leucine specific-binding protein (LS) and the leucine-isoleucine-valine binding protein (LIV), have high similarity in their structure and function, but show different substrate specificity. A key difference between these proteins is residue 18 in the binding pocket, a tryptophan residue in LS and a tyrosine residue in LIV. To examine the role of this residue in binding specificity, we used fluorescence and F-19 NMR to monitor ligand binding to three mutants: LSW18Y, LSW18F and LIV18W. We observed leucine binding to all proteins. LS binds L-phenylalanine but the mutation from Trp to Tyr or Phe disallows this ligand and expands the binding repertoire to L-isoleucine and L-valine. The LIVY18W mutant still retains the ability to bind L-isoleucine and also binds L-phenylalanine.

F-19 NMR; leucine-binding protein; fluorescence; periplasmic binding protein

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