Discovery of an l-fucono-1,5-lactonase from cog3618 of the amidohydrolase superfamily

A member of the amidohydrolase superfamily, BmulJ-04915 from Burkholderia multivorans, of unknown function was determined to hydrolyze a series of sugar lactones: l-fucono-1,4-lactone, d-arabino-1,4-lactone, l-xylono-1,4-lactone, d-lyxono-1,4-lactone, and l-galactono-1,4-lactone. The highest activity was shown for l-fucono-1,4-lactone with a k_cat value of 140 s ^-1 and a k_cat/K_m value of 1.0 × 10 ⁵ M^-1 s^-1 at pH 8.3. The enzymatic product of an adjacent l-fucose dehydrogenase, BmulJ-04919, was shown to be l-fucono-1,5-lactone via nuclear magnetic resonance spectroscopy. l-Fucono-1,5-lactone is unstable and rapidly converts nonenzymatically to l-fucono-1,4-lactone. Because of the chemical instability of l-fucono-1,5-lactone, 4-deoxy-l-fucono-1,5-lactone was enzymatically synthesized from 4-deoxy-l-fucose using l-fucose dehydrogenase. BmulJ-04915 hydrolyzed 4-deoxy-l-fucono-1,5-lactone with a k_cat value of 990 s^-1 and a k_cat/K_m value of 8.0 × 10⁶ M ^-1 s^-1 at pH 7.1. The protein does not require divalent cations in the active site for catalytic activity. BmulJ-04915 is the second enzyme from cog3618 of the amidohydrolase superfamily that does not require a divalent metal for catalytic activity. BmulJ-04915 is the first enzyme that has been shown to catalyze the hydrolysis of either l-fucono-1,4-lactone or l-fucono-1,5-lactone. The structures of the fuconolactonase and the fucose dehydrogenase were determined by X-ray diffraction methods.