The Making of a “Super”-Enzyme

Oeiras, 22.05.09

When investigating the role of particular aminoacids in the bacterial enzyme RNase II, researchers from the Control of Gene Expression Laboratory and co-workers discovered that the mutation of a single aminoacid turned RNase II into a “super”-enzyme with extraordinary catalytic power. The results are published in the Journal of Biological Chemistry.

The growing acknowledgement that RNA’s metabolism is finely tuned in living cells makes it essential to understand the mechanism by which it is degraded. Exoribonuclease II (RNase II) is the prototype of an ubiquitous family of enzymes that are crucial for RNA degradation in both prokaryotes and eukaryotes. By analyzing the previously reported 3D structure of RNase II, researchers identified those residues most likely to be involved in RNA binding and cleavage and set to see how the enzyme would behave if those residues were replaced by others.

While all aminoacids contribute to a protein’s identity some are more important than others for the protein’s function. In the case of RNase II the researchers determined that two residues (tyrosine in position 313 and glutamate in position 390) are crucial for the RNA specificity, and that a third one (arginine in position 500) is essential for catalysis but not RNA binding. More surprisingly, the replacement of a glutamate (position 542) by an alanine caused the mutant protein to bind RNA (20 times) more tightly than the wild-type enzyme and increased its catalytic activity by over 100 fold. The results from this work can be extrapolated for the engineering of “super”- enzymes.

Original paper: 

JBC published May 19, 2009 as doi:10.1074/jbc.M109.020693

Determination of key residues for catalysis and RNA-cleavage specificity: one mutation turns RNase II into a "super"-enzyme.

Ana Barbas, Rute G. Matos, Monica Amblar (2), Eduardo López-Viñas (3), Paulino Gomez-Puertas (3), and Cecília M. Arraiano

2 - Instituto de Salud Carlos III Madrid, Spain; 3- CSIC-Univ. Autónoma de Madrid, Spain
A.B. and R.G.M. contributed equally to this work 
Corresponding author: Cecília Arraiano