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PubMed1996

Expression of lignin peroxidase H8 in Escherichia coli: folding and activation of the recombinant enzyme with Ca2+ and haem.

An engineered cDNA from Phanerochaete chrysosporium encoding both the mature and pro-sequence regions of Lip isoenzyme H8 (Lip) has been successfully overexpressed in Escherichia coli. The recombinant protein (LipP*) was sequestered in inclusion bodies. The reduced-denatured polypeptide has been purified by differential solubilization, and the active enzyme recovered after controlled in vitro refolding (albeit in low yield), by glutathione-mediated oxidation of disulphides, in a folding medium containing an intermediate concentration of urea, Ca2+, and haem. The procedure is analogous to that previously described for the production of active recombinant horseradish peroxidase (HRP-C*) from inclusion-body material. It is quite possible, therefore, that this type of procedure may be suitable for the recovery of most, if not all, active recombinant peroxidases. The resultant LipP* has spectral characteristics identical with that of the native enzyme as isolated from Phanerochaete chrysosporium. Its specific activity measured in the standard veratryl alcohol (VA) assay was 39 micromol of VA oxidized/min per mg of protein, a value which compares extremely favourably with that of the native enzyme (36 micromol of VA/min per mg). Although levels of active enzyme obtained are not yet as high as in the case of HRP-C* (1% conversion of crude inactive LipP* polypeptide into pure fully active Lip), it is envisaged that further refinement of the expression/folding/activation procedures will provide sufficient protein for biophysical characterization of both the wild-type and site-directed mutants.

Base Sequence↗
PubMed1995

A beta-glucosidase from lodgepole pine xylem specific for the lignin precursor coniferin.

Coniferin, the glucoside of the monolignol coniferyl alcohol, accumulates to high levels in gymnosperms during spring-cambial reactivation. A cinnamyl alcohol glucoside/beta-glucosidase system is thought to play a key role in lignification by releasing the monolignol aglycones. Investigation of such an enzyme system in the xylem of Pinus contorta var latifolia Engelm. revealed two major beta-glucosidases. One efficiently hydrolyzed the native substrate, coniferin, and the other was more active against synthetic glucosides. The coniferin beta-glucosidase was purified to apparent homogeneity using anion exchange, hydrophobic interaction, and size-exclusion chromatography. The apparent native molecular weight was estimated to be 60,000. A dominant 28-kD protein and a minor 24-kD protein were detected in the purified preparation following sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Immunological evidence from polyclonal antibodies directed against the synthetic N-terminal peptide of the 24-kD protein suggested that the native protein is a dimer of 28-kD subunit size. The N-terminal sequence showed that coniferin beta-glucosidase has high homology to known plant beta-glucosidases. Coniferin, syringin, and a synthetic coniferin analog were preferred substrates for the coniferin beta-glucosidase. In situ localization using the chromogenic coniferin analog showed the exclusive presence of beta-glucosidase activity in the differentiating xylem, similar to peroxidase activity.

Amino Acid Sequence↗