Although the catalytic center of an enyzme is usually
highly conserved, there have been a few reports of proteins with substitutions
at essential catalytic positions, which convert the enyzme into a catalytically
inactive form. In order to gain insight into the function
and evolution of inactive enzyme-homologues a large-scale analysis
of substitutions at enzymes' catalytic sites was performed. The
analysis revealed that inactive enzyme-homologues are not an exception
only found in single enzyme families, but that they are represented
in a large variety of enzyme families and conserved among metazoan
species. Even though they have lost their catalytic activity,
they have adopted new functions and are now mainly involved in regulatory
processes, which I will discuss in detail using the protein tyrosine
The modification of existing modules is an efficient mechanism to
evolve new functions. The invention of inactive enzyme-homologues
in metazoa has thereby led to an enhancement of complexity of regulatory networks.
Pils B, Schultz J. Inactive Enzyme-homologues Find New Function in Regulatory
Processes. J Mol Biol. 2004 Jul 9;340(3):399-404.
Pils B, Schultz J. Evolution of the multifunctional protein tyrosine phosphatase
family. Mol Biol Evol. 2004 Apr;21(4):625-31.