Heterologous expression of polyhydroxyalkanoate depolymerase from Thermobifida sp. in Pichia pastoris and catalytic analysis by surface plasmon resonance

Abstract

A polyhydroxyalkanote depolymerase gene from Thermobifida sp. isolate BCC23166 was cloned and expressed as a C-terminal His6-tagged fusion in Pichia pastoris. Primary structure analysis revealed that the enzyme PhaZ-Th is a member of a proposed new subgroup of SCL-PHA depolymerase containing a proline-serine repeat linker. PhaZ-Th was expressed as two glycosylated forms with apparent molecular weights of 61 and 70 kDa, respectively. The enzyme showed esterase activity toward p-nitrophenyl alkanotes with Vmaxand Kmof 3.63∈±∈0.16 μmol min-1mg-1and 0.79∈±∈0.12 mM, respectively, on p-nitrophenyl butyrate with optimal activity at 50-55°C and pH 7-8. Surface plasmon resonance (SPR) analysis demonstrated that PhaZ-Th catalyzed the degradation of poly-[(R)-3-hydroxybutyrate] (PHB) films, which was accelerated in (R)-3-hydroxyvalerate copolymers with a maximum degradation rate of 882 ng cm-2h-1for poly[(R)-3-hydroxybutyrate-co-3- hydroxyvalerate] (12 mol% V). Surface deterioration, especially on the amorphous regions of PHB films was observed after exposure to PhaZ-Th by atomic force microscopy. The use of P. pastoris as an alternative recombinant system for bioplastic degrading enzymes in secreted form and a sensitive SPR analytical technique will be of utility for further study of bioplastic degradation. © 2008 Springer-Verlag.