The two types of 3-dehydroquinase have distinct structures but catalyze the same overall reaction.
Gourley, D.G., Shrive, A.K., Polikarpov, I., Krell, T., Coggins, J.R., Hawkins, A.R., Isaacs, N.W., Sawyer, L.(1999) Nat Struct Biol 6: 521-525
- PubMed: 10360352 
- DOI: 10.1038/9287
- Primary Citation of Related Structures:  
1QFE, 2DHQ - PubMed Abstract: 
The structures of enzymes catalyzing the reactions in central metabolic pathways are generally well conserved as are their catalytic mechanisms. The two types of 3-dehydroquinate dehydratase (DHQase) are therefore most unusual since they are unrelated at the sequence level and they utilize completely different mechanisms to catalyze the same overall reaction ...