RIBOZYME

1. RIBOZYME Submitted By: Karabee Dutta M.Sc.2nd sem. Roll No:18(181)

2. DEFINATION: • A ribozyme is an RNA molecule with a well defined tertiary structure . • Ribozyme means ribonucleic acid enzyme. It may also be called an RNAenzyme or catalytic RNA. It contains an active site that consists entirely of RNA.

3. A ribozyme can catalyzes a chemical reaction. Many natural ribozymes catalyze either the hydrolysis of one of their own phosphodiester bonds(self-cleaving ribozymes), or the hydrolysis of bonds in other RNAs. • They have been found to catalyze the aminotransferase activity of the ribosome. • Examples of ribozymes include the hammerhead ribozyme, the VS ribozyme and the hairpin ribozyme.

4. DISCOVERY OF RIBOZYME: • Before the discovery of ribozymes, enzymes, which are defined as catalytic proteins, were the only known biological catalysts. • In 1967, Carl Woese, Francis Crick, and Leslie Orgel were the first to suggest that RNA could act as a catalyst. •  The first ribozymes were discovered in the 1980s by Thomas R. Cech, who was studying RNA splicing in the ciliatedprotozoanTetrahymena thermophila and Sidney Altman, who was working on the bacterial RNase P complex.

5. These ribozymes were found in the intron of an RNA transcript, which removed itself from the transcript, as well as in the RNA component of the RNase P complex, which is involved in the maturation of pre-tRNAs. • In 1989, Thomas R. Cech and Sidney Altman won the Nobel Prize inchemistry for their "discovery of catalytic properties of RNA.” •  The term ribozyme was first introduced by Kelly Kruger et al. in 1982 in a paper published in Cell.

6. Schematic showing ribozyme cleavage of RNA:

7. Structure Hammerhead Ribozyme :

8.       Figure : Secondary structures of in cis and in trans hammerhead ribozymes.

9. Figure : Turnover cycle of RNA cleavage by a hammerhead ribozyme. Binding of the enzyme and substrate results in the catalytically active structure. After cleavage, the two product strands dissociate and the ribozyme strand can go into the next cycle.

10. Activity: • Although most ribozymes are quite rare in the cell, their roles are sometimes essential to life. • For example, the functional part of the ribosome, the molecular machine that translates RNA into proteins, is fundamentally a ribozyme, composed of RNA tertiary structural motifs that are often coordinated to metal ions such as Mg2+ as cofactors. • RNA can also act as a hereditary molecule,  Walter Gilbert  propose that, the cell used RNA as both the genetic material and the structural and catalytic molecule. This hypothesis is known as the "RNA world hypothesis" of the origin of life.

11. A recent test-tube study of prionfolding suggests that an RNA may catalyze the pathological protein conformation in the manner of a chaperone enzyme. • Ribozymes have been shown to be involved in the viral concatemer cleavage that precedes the packing of viral genetic material into virions.

12. Naturally occurring ribozymes include: • Peptidyl transferase 23S rRNA • RNase P • Group I and Group II introns • GIR1 branching ribozyme • Leadzyme • Hairpin ribozyme

13. Hammerhead ribozyme • HDV ribozyme • Mammalian CPEB3 ribozyme • VS ribozyme • glmS ribozyme • CoTC ribozyme • Almost all living things synthesize an enzyme — called Ribonuclease P (RNase P) — that cleaves the head (5') end of the precursors of transfer RNA (tRNA) molecules.

14. Artificial ribozymes: • The synthetic ribozymes made in the laboratory are known as artificial ribozymes. • Tang and Breakerisolated self-cleaving RNAs by in vitro selection of RNAs originating from random-sequence RNAs.One approach for selecting a ligase ribozyme involves using biotin tags, which are covalently linked to the substrate. • Some synthetic ribozymes have novel structures, while some were similar to the naturally occurring hammerhead ribozyme.

15. The techniques used to discover artificial ribozymes involve Darwinian evolution. This approach takes advantage of RNA's dual nature as both a catalyst and an informational polymer, making it easy for an investigator to produce vast populations of RNA catalysts using polymerase enzymes. • The ribozymes are mutated by reverse transcribing them with reverse transcriptase into various cDNA and amplified with mutagenic PCR. • Lincoln and Joyce developed an RNA enzyme system capable of self replication by utilizing molecular competition (in vitro evolution).

16. Applications: • A type of synthetic ribozyme directed against HIV RNA called gene shears has been developed and has entered clinical testing for HIV infection • Ribozymes for Human Therapy: The ability of ribozymes to recognize and cut specific RNA molecules makes them exciting candidates for human therapy.

17. Thank you....!