Oh and another thing, apparently the function of this specific class of enzymes has evolved independently in bacteria in a completely different protein, which was already an enzyme. So apparently this function can be reached from wildly different positions in protein sequence space. From the OP paper:
Discussion
Our results indicate that CHI evolved from a catalytically inactive ancestor, thus demonstrating that emergence of catalysis and stereospecificity in noncatalytic scaffolds is a feasible evolutionary scenario. That said, a bacterial CHI29 has evolved independently in an enzymatic protein fold, exemplifying that plant CHI is an exception rather than the rule.
The bacterial CHI referenced in 29 apparently evolved from a Ferredoxin-fold enzyme and stress-related protein. In that paper (29) we can read:
4. Conclusion
The two-domain structure of the bacterial CHI is closely related to the ferredoxin-like fold of a chlorite dismutase and the stress-related protein SP1, despite the lack of any functional relationship. The tertiary structure of bacterial CHI, with ferredoxin-like folds, is completely different to that of the plant CHI, suggesting that the enzymes evolved convergently from different ancestor proteins. The bacterial CHI is only related to the plant CHI with respect to the products of the catalysed oxa-Michael addition.
Apparently the bacterial enzyme is also about 20 times more efficient than the plant enzyme.