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Structure and mechanism of a bacterial haloalcohol dehalogenase: a new variation of the short‐chain dehydrogenase/reductase fold without an NAD(P)H binding site
Author(s) -
de Jong R. M.,
Tiesinga J. J. W.,
Rozeboom H. J.,
Kalk K. H.,
Tang L.,
Janssen D. B.,
Dijkstra B. W.
Publication year - 2003
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/cdg479
Subject(s) - nad+ kinase , active site , dehalogenase , stereochemistry , catalytic triad , cofactor , biology , binding site , dehydrogenase , oxidoreductase , biochemistry , enzyme , chemistry
Haloalcohol dehalogenases are bacterial enzymes that catalyze the cofactor‐independent dehalogenation of vicinal haloalcohols such as the genotoxic environmental pollutant 1,3‐dichloro‐2‐propanol, thereby producing an epoxide, a chloride ion and a proton. Here we present X‐ray structures of the haloalcohol dehalogenase HheC from Agrobacterium radiobacter AD1, and complexes of the enzyme with an epoxide product and chloride ion, and with a bound haloalcohol substrate mimic. These structures support a catalytic mechanism in which Tyr145 of a Ser‐Tyr‐Arg catalytic triad deprotonates the haloalcohol hydroxyl function to generate an intramolecular nucleophile that substitutes the vicinal halogen. Haloalcohol dehalogenases are related to the widespread family of NAD(P)H‐dependent short‐chain dehydrogenases/reductases (SDR family), which use a similar Ser‐Tyr‐Lys/Arg catalytic triad to catalyze reductive or oxidative conversions of various secondary alcohols and ketones. Our results reveal the first structural details of an SDR‐related enzyme that catalyzes a substitutive dehalogenation reaction rather than a redox reaction, in which a halide‐binding site is found at the location of the NAD(P)H binding site. Structure‐based sequence analysis reveals that the various haloalcohol dehalogenases have likely originated from at least two different NAD‐binding SDR precursors.