Structural consequences of two methyl additions in the E. coli trp repressor L-tryptophan binding pocket

摘要

The flexibility and specificity of the L-tryptophan corepressor binding pocket of E coli trp repressor are being investigated by high-resolution crystallographic examination of aporepressor/corepressor analog complexes. While addition of a methyl group on the corepressor indole (5-methyl-tryptophan) results in a small but measurable shift in the position of that functional group introduction of a methyl group on a nearby residue in the binding pocket (Val 58 (yields) Ile) leaves the indole position of L-tryptophan essentially unchanged. Careful alignment of these structures with aporepressor/L- tryptophan/operator-DNA complexes reveal why 5-methyltryptophan is a better corepressor than L-tryptophan.