Towards a new T-fold protein?: the coproporphyrinogen III oxidase sequence matches many structural features from urate oxidase.

Urate oxidase (UOX) and coproporphyrinogen III oxidase (CPO) are two unusual oxidases as they accomplish their catalytic act with no co-factor nor metal ion. They both require molecular oxygen, and lead to hydrogen peroxide in addition to the product. UOX is composed of two contiguous Tunneling-fold domains and CPO appears to be also divided into two structurally equivalent domains. Moreover, each of these putative domains can be coherently aligned on UOX domains. Although their sequences are very distant, we therefore suggest that functional CPO dimer is built around a tunnel, with the substrate sitting above it, on the N- and C-terminal side. This overall model is supported by mutation data and is coherent with the chemical events expected for substrate processing by CPO.