Flavin-dependent halogenases chlorinate or brominate their substrates in an environmentally friendly manner, only requiring the cofactor reduced flavin adenine dinucleotide (FADH(2)), oxygen, and halide salts. The tryptophan 6-halogenase Thal exhibits two flexible loops, which become ordered (substrate-binding loop) or adopt a closed conformation (FAD loop) upon substrate or cofactor binding. Here, we describe the structure of N-His-Thal-RebH5 containing an N-terminal His-tag from pET28a, which crystallized in a different space group (P2(1)) and, surprisingly, diffracted to a higher resolution of 1.63 angstrom than previously deposited Thal structures (P6(4); similar to 2.2 angstrom) with cleaved His-tag. Interestingly, the binding of glycine in the active site can induce an ordered conformation of the substrate-binding loop.
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