ナイロンオリゴマー分解酵素・NylBの構造と進化(<特集2>シンポジウム「立体構造からみたタンパク質の進化」)

概要

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Arthrobacter sp. (formerly Flavobacterium sp.) KI72 has enzymes which are responsible for the degradation of nylon-6 industry by-products (nylon-oligomer). NylB encoded on plasmid pOAD2 is one of these enzymes and has a specific activity toward the degradation of 6-aminohexanoate-linear dimer (Ald). The plasmid, pOAD2, has also an analogous protein, NylB', which has 88% homology to NylB but only about 0.5% of the specific activity. We constructed Hyb24 (a hybrid between the NylB and NylB' with NylB'-level activity), Hyb24DN (with double mutation of G181D and H266N with NylB-level activity) and Hyb24DNA (a mutant of Hyb24DN with an additional mutation of S112A at the active site) proteins and solved the three-dimensional structures by x-ray crystallography. In case of Hyb24DNA, the structure of a complex with substrate, Ald, was determined. The overall structures of three proteins are almost identical with a two-domain structure that is categorized in β-lactamase fold. On the basis of the spatial arrangements of amino acid residues at the active site of Hyb24DN and Hyb24DNA-Ald complex, we conclude that the nylon-oligomer hydrolase has evolved from the ester hydrolysis enzymes, of which essential residue is nucleophilic Ser112, with a β-lactamase fold as an ancestral protein by substitution of two residues G181D and H266N at the active site pocket.
2010-03-01