Crystal structures of Phanerochaete chrysosporium pyranose 2‐oxidase suggest that the N‐terminus acts as a propeptide that assists in homotetramer assembly. Issue 1 (5th November 2013) - Hassan, Noor
Abstract : The flavin‐dependent homotetrameric enzyme pyranose 2‐oxidase (P2O) is found mostly, but not exclusively, in lignocellulose‐degrading fungi where it catalyzes the oxidation of β ‐d ‐glucose to the corresponding 2‐keto sugar concomitantly with hydrogen peroxide formation during lignin solubilization. Here, we present crystal structures of P2O from the efficient lignocellulolytic basidiomycete Phanerochaete chrysosporium . Structures were determined of wild‐type Pc P2O from the natural fungal source, and two variants of recombinant full‐length Pc P2O, both in complex with the slow substrate 3‐deoxy‐3‐fluoro‐ β ‐d ‐glucose. The active sites in Pc P2O and P2O from Trametes multicolor ( Tm P2O) are highly conserved with identical substrate binding. Our structural analysis suggests that the 17 °C higher melting temperature of Pc P2O compared to Tm P2O is due to an increased number of intersubunit salt bridges. The structure of recombinant Pc P2O expressed with its natural N‐terminal sequence, including a proposed propeptide segment, reveals that the first five residues of the propeptide intercalate at the interface between A and B subunits to form stabilizing, mainly hydrophobic, interactions. In the structure of mature Pc P2O purified from the natural source, the propeptide segment in subunit A has been replaced by a nearby loop in the B subunit. We propose that the propeptide in subunit A stabilizes the A/B interface of essential dimers in the homotetramer and that, upon maturation, it is replaced by the loop in the B subunit to form the mature subunit interface. This would imply that the propeptide segment of Pc P2O acts as an intramolecular chaperone for oligomerization at the A/B interface of the essential dimer. Abstract : Structures of pyranose 2‐oxidase from Phanerochaete chrysosporium were determined. The N‐terminus may act as a propeptide with a role in homotetramer assembly. A large number of salt bridges between subunits provides thermostability. The substrate is bound in the productive binding mode for oxidation at C2.