The Active Site Of A Carbohydrate Esterase Displays Divergent Catalytic And Noncatalytic Binding Functions

Multi-functional proteins have typically evolved through the recruitment of different domains, each of which has a specific function. Thus, in a
multifunctional protein, the different functions are mediated by spatially distinct domains, or modules, such that a single domain can provide the
specific chemical requirements for one activity.




Indeed current evolutionary theory argues that the co-localization of diverse activities within a
single-domain enzyme is likely to be a rare event as it would compromise the existing activity of the protein when a new function evolves.
Nonetheless, a potential example of multifunctional recruitment into a single protein domain is provided by an enzyme that contains a cellulase enzyme
module and a discrete non-catalytic cellulose-binding module. In this article, Harry Gilbert and colleagues at Newcastle University show that the
cellulose-binding module displays esterase (cellulase) activity and that these diverse activities are housed within the same site on the protein.




Structural analysis of the enzyme reveals that its catalytic residues contribute to the non-catalytic cellulose-binding function. This report provides
a rare example of 'gene sharing', whereby the introduction of a second functionality into the active site of an enzyme does not compromise the
original activity of the catalyst.




Citation:


"The active site of a carbohydrate esterase displays divergent catalytic and noncatalytic binding functions."

Montanier C, Money VA, Pires VMR, Flint JE, Pinheiro BA, et al. (2009)


PLoS Biol 7(3): e1000071. doi:10.1371/journal.pbio.1000071




Source
Public Library of Science