Abstract

A bacterial strain M4-7 capable of degrading various polyesters, such as poly(e-caprolactone), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxyoctanoate), and poly(3-hydroxy-5-phenylvalerate), was isolated from a marine environment and identified as Pseudomonas alcaligenes. The relative molecular mass of a purified extracellular medium-chain-length poly(3-hydroxyalkanoate) (MCL-PHA) depolymerase (PhaZ_PalM4-7) from P. alcaligenes M4-7 was 28.0 kDa, as determined by SDS-PAGE. The PhaZ_PalM4-7 was most active in 50 mM glycine-NaOH buffer (pH 9.0) at 35^oC. It was insensitive to dithiothreitol, sodium azide, and iodoacetamide, but susceptible to p-hydroxymercuribenzoic acid, N-bromosuccinimide, acetic anhydride, EDTA, diisopropyl fluorophosphate, phenylmethylsulfonyl fluoride, Tween 80, and Triton X-100. In this study, the genes encoding MCL-PHA depolymerase were cloned, sequenced, and characterized from a soil bacterium, P. alcaligenes LB19 (Kim et al., 2002, Biomacromolecules 3, 291-296) as well as P. alcaligenes M4-7. The structural gene (phaZ_PalLB19) of MCL-PHA depolymerase of P. alcaligenes LB19 consisted of an 837 bp open reading frame (ORF) encoding a protein of 278 amino acids with a deduced M_r of 30,188 Da. However, the MCL-PHA depolymerase gene (phaZ_PalM4-7) of P. alcaligenes M4-7 was composed of an 834 bp ORF encoding a protein of 277 amino acids with a deduced M_r of 30,323 Da. Amino acid sequence analyses showed that, in the two different polypeptides, a substrate-binding domain and a catalytic domain are located in the N-terminus and in the C-terminus, respectively. The PhaZ_PalLB19 and the PhaZ_PalM4-7 commonly share the lipase box, GISSG, in their catalytic domains, and utilize ^111Asn and ^110Ser residues, respectively, as oxyanions that play an important role in transition-state stabilization of hydrolytic reactions.

• Keywords: Medium-chain-length polyhydroxyalkanoate; polyhydroxyalkanoate depolymerase; Pseudomonas alcaligenes