Not all Enzymatic Reactions Are Catalyzed by Protein

It had been a firmly established belief in biology that catalysis is reserved for proteins. However in 1989 the Nobel Prize was presented to Sidney Altman and Tomas Cech for discovering that RNA can catalyze a reaction. In respect, catalytic RNA make s a lot of sense. This is based on the old question regarding the origin of life, which comes first, enzyme that do the work of the cell or nucleic acids that carry the information required to produce the enzymes ? Nucleic acids as catalysts circumvents this problem.

Research leading to the discovery that RNA can act as a catalyst started in the 1970’s. Thomas Cech , at the university of Colorado at Boulder, was studying the excision of introns in a ribosomal RNA gene in Tetrahymena thermophila. In attempting to purify the enzyme responsible for splicing reaction, he instead found , much of his amazement , that intron could be spliced –out in the absence of any added cell extract. Much as they tried, Cech and his colleagues could not identify any protein associated with the splicing reaction,. After much work , Cech proposed that the intron sequence portion of the RNA had properties of an enzyme enabling it to break and reform phosphodiester bonds. At about the same time, Sidney Altman, who is a Professor at Yale university was studying the way tRNA molecules are processed in the cell when he and his colleagues isolated a enzymes called RNase-P, which is responsible for conversion of a precursor tRNA into the active tRNA. Much of their surprise, they found that RNase-P contained RNA in addition to protein and that RNA was an essential component of the active enzyme. This was such a foreign idea that they had difficulty publishing their findings. The following year, Altman Demonstrated the final bit of evidence establishing that RNA can act as a catalyst by showing that the RNase-P RNA submit could catalyze the cleavage of precursor tRNA into active tRNA in the absence of the protein component.

Since Cech’s and Altman’s discovery, other investigators have discovered other example of self-cleaving RNA sot catalytic RNA molecules dubbed ribozymes have either a hairpin – or hammerhead – shaped active center and a unique secondary structure allowing them to cleave other RNA molecules at specific sequences. It is possible to produce in the laboratory ribozymes that will specifically cleave my RNA molecule. These RNA catalysts may have pharmaceuticals applications. For example , a ribozyme has been designed to cleave the RNA of HIV. By placing a ribozyme in the cell all incoming virus particles that express this particular gene will have the RNA product cleaved by the ribozyme, which ,in the end would kill all invading virus particles.