Recombinant expression, purification and biochemical characterization of kievitone hydratase from Nectria haematococca.

Kievitone hydratase catalyzes the addition of water to the double bond of the prenyl moiety of plant isoflavonoid kievitone and, thereby, forms the tertiary alcohol hydroxy-kievitone. In nature, this conversion is associated with a defense mechanism of fungal pathogens against phytoalexins generated by host plants after infection. As of today, a gene sequence coding for kievitone hydratase activity has only been identified and characterized in Fusarium solani f. sp. phaseoli. Here, we report on the identification of a putative kievitone hydratase sequence in Nectria haematococca (NhKHS), the teleomorph state of F. solani, based on in silico sequence analyses. After heterologous expression of the enzyme in the methylotrophic yeast Pichia pastoris, we have confirmed its kievitone hydration activity and have assessed its biochemical properties and substrate specificity. Purified recombinant NhKHS is obviously a homodimeric glycoprotein. Due to its good activity for the readily available chalcone derivative xanthohumol (XN), this compound was selected as a model substrate for biochemical studies. The optimal pH and temperature for hydratase activity were 6.0 and 35°C, respectively, and apparent V_max and K_m values for hydration of XN were 7.16 μmol min^-1 mg^-1 and 0.98 ± 0.13 mM, respectively. Due to its catalytic properties and apparent substrate promiscuity, NhKHS is a promising enzyme for the biocatalytic production of tertiary alcohols. [ABSTRACT FROM AUTHOR]