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Different Types of Ribozymes

Posted by The Protein Man on Feb 7, 2024 3:36:06 PM
The Protein Man


Different Types of Ribozymes

Ribozymes (ribonucleic acid enzymes) are RNA molecules that can catalyze certain biochemical reactions, including RNA cleavage and modification, ligation, peptide bond formation, and viral replication, without relying on enzymes. 

Mechanism of Action

Ribozymes leverage RNA's chemical properties to catalyze a specific reaction, which typically consists of three steps: substrate binding, catalysis, and product release.

When a ribozyme interacts with a specific RNA molecule, it is called substrate binding.  As the ribozyme binds with the target RNA, a conformational change occurs, bringing the ribozyme's active site closer to the target RNA.

The second step is catalysis. This happens when the ribozyme facilitates a specific chemical reaction (acid-base catalysis, nucleophilic attack, or metal ion coordination) using its distinct chemical properties.

The final step is product release. Upon the completion of the catalytic reaction, the products are released and can bind to a new substrate or undergo a conformational change.  

Types of Ribozymes

Ribozymes are broadly classified as either small or large. Small ribozymes are typically composed of 30 to 150 nucleotides, whereas large ribozymes are a few hundred to a few thousand nucleotides in length. The activity of small ribozymes does not rely on metal ions, whereas larger ones do. 

The hairpin, hammerhead, and VS ribozymes are fine examples of small ribozymes, while large ribozymes include Ribonuclease P (RNase P) and the self-splicing introns (Group I and Group II introns).  

Hairpin ribozymes

These ribozymes, mostly found in plant viruses, are structurally similar to the hammerhead ribozyme but exhibit a different mechanism of action. Because these ribozymes can specifically cleave RNA sequences that are complementary to their own, they are an intriguing target for therapeutic applications.

Hammerhead ribozymes

Many plant viruses contain these small, self-cleaving RNA molecules. Generally, their function can be compared to tiny molecular scissors since they cleave RNA sequences at precise locations. These ribozymes have been utilized in molecular biology studies to modify RNA sequences and study gene expression.

Hepatitis delta virus ribozymes

HPV ribozymes, which are essentially non-coding RNAs discovered in the hepatitis delta virus, break the viral RNA genome to produce smaller fragments that function as replication templates. By targeting these ribozymes, developing treatments for HPV infection is entirely possible.

VS ribozyme

Found mainly in viruses, this stem loop-shaped ribozyme regulates viral gene expression by cleaving specific RNA sequences in a magnesium-dependent manner.

RNase P

Basically, RNase P is involved in the processing of tRNA molecules. It works by cleaving the precursor tRNA to generate the mature tRNA for ribosomal use.

Self-splicing introns

These ribozymes, typically found within pre-mRNA molecules of many eukaryotic organisms and some bacteria, can catalyze their removal from the primary transcript, leaving only the mature mRNA behind. This is incredibly significant since it suggests that RNA molecules can actively regulate gene expression rather than simply acting as passive intermediaries.

    • Group I introns. These ribozymes have the ability to self-splice from the RNA transcript as well as catalyze RNA cleavage and ligation events.
  • Group II introns. While structurally similar to Group I introns, these ribozymes have a more complex splicing mechanism. The existence of Group II introns in bacteria and eukaryotic organelles such as mitochondria and chloroplasts suggest a shared evolutionary past.

Some other examples are as follows:

  • GIR1 branching ribozyme - catalyzes the production of branched RNA.
  • Pistol ribozyme - an RNA molecule that looks like a pistol and has a trigger-like mechanism that cleaves particular RNA sequences and regulates gene expression. 
  • Twister and twister sister ribozymes - RNA processing and gene regulatory enzymes.
  • Hatchet ribozyme - a ribozyme with a "sharp" active site capable of cleaving certain RNA sequences.

Aside from playing important roles in many biological processes (e.g. RNA processing, replication of RNA viruses, and gene expression regulation), these diverse and fascinating groups of RNA molecules are also used as tools for molecular biology research and hold potential as therapeutic agents for a variety of diseases. 



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