Although the catalytic machinery is fully conserved, careful analysis of sequence conservation in the active site area revealed that the human and fungal enzymes possess differences near the substrate-binding site.
In the case of APAO, instead, there seems to be a lower evolutionary pressure towards strict conservation of the active site residues, the only residues conserved in more than 90% of the sequences analysed being Trp62, His64, Tyr430, Ser473 and Thr474 (ortholog to SMO residues Trp80, His82, Tyr482, Ser527 and Thr528), besides the catalytically important Lys315.
However, the strict conservation between the active site residues in the N-terminal half of the eukaryotic enzyme and those of bacterial PFK1s suggests that the only active site in the eukaryotic enzyme is located in the N-terminus [3].
The remarkable conservation of the active site area explains the identity of function between eukarial and prokarial tyrosinases with eukarial enzyme acquiring during evolution specific molecular determinants such as the Cys1 domain, the TM domain and the seven N-linked glycans.
The CTX-M enzymes are also distinguished by the conservation of the active site residues Ser237 and Arg276 in that this combination does not occur in other class A β-lactamases.
Nonetheless, Cg-Slx1-DNA interactions can be modeled based on the conservation of the active site between Slx1 and GIY-YIG restrictases, for which high-resolution protein-DNA structures are available.
An alignment of all cathepsin L predicted protein sequences from T. castaneum and T. molitor demonstrated sequence conservation of the active site residues QCHN in the majority of the sequences (Additional file 2: Figure S1).
A high degree of sequence conservation in the active sites of retroviral INs allowed the use of the PFV intasome as a surrogate for its HIV-1 counterpart (Hare et al, 2010a, 2010b, 2011).
Crystallographic analyses have also revealed the PD-(D/E XK fold in proteins that do not function as deoxyribonucleases at all and exhibit no conservation of the active site with the above-mentioned enzymes.
Hence there is a need for CA isoform specific inhibitors to avoid off-target CA inhibition, but due to the high amino acid conservation of the active site and surrounding regions between each enzyme, this has proven difficult.
