Antibiotics and Toxins which inhibits protein synthesis in prokaryotes and eukaryotes.

Antibiotics and Toxins which inhibits protein synthesis in prokaryotes and eukaryotes.

There are some examples of Antibiotics and Toxins;

Prokaryotic protein inhibitors :-

1. Streptomycin :-

                              🐣Streptomycin is a basic trisaccharide, which binds with 30 S ribosomal subunit of prokaryotes (ie. bacteria).

🐣It cause misreading of mRNA.

2. Chloramphenicol :-

                                     🐣It binds to 50 S subunit of ribosome in bacteria and block peptide bond formation, but how? because it inhibits peptidyl transferase. But it does not affect cytosolic protein synthesis in eukaryotes.

3. Tetracycline :-

                           🐣An antibiotic that bind to 30 S subunit  of ribosome and interferes with amino acyl - tRNA binding. 

4. Erythromycin :-

                             🐣Erythromycin binds with 50 S ribosomal subunit and inhibits peptide chain elongation.

5. Fusidic acid :-

                           🐣Binds to elongation factor-G (EF-G) and blocks translocation. 

Eukaryotic inhibitors of protein synthesis :-

6. Cytohexamide :-

                               🐣 Blocks peptidyl transferase of 80 S ribosome but not that of 70 S bacterial ( mitochondrial & chloroplast) ribosomes. 

7. Diptheria toxin :-

                                🐣 Produced by Cynobactetium diptheriae in specific temperate phase (cynohase B) is an exotoxin, and stop protein synthesis in eukaryotic cells,  but how? It's by inactivation of elongation factor eEF2 and it occurs due to ADP ribosylation which is catalyzed by a fragment of toxin.

8. Ricin :-

               🐣 Ricin is a toxic protein which is procuced caster bean (Ricinus communis).

🐣 In eukaryotic cells it inactivate 60 S subunit of ribosomes by depurinating a specific adenosine in 28 S rRNA.

6. Puromycin :-

                        🐣 In Streptomyces alboniger puromycin is a secondary metabolite and block protein biosynthesis.

🐣The structure of puromycin is structural analogue of 3' end of aminoacyl tRNA, but difference in both of them is linked to ribose.

🐣 Usually 3' end of tRNA binds with amino acid via an aster bond but in case of puromycin analogue 3' end of tRNA binds with puromycin via an amide bond.

🐣 Like aminoacyl-tRNA puromycin binds to A- site of ribosome peptidyltransferase center.

🐣 Now A- site of ribosome accupied by puromycin, peptidyltransferase links peptide residues of peptidyl-tRNA in ribosome p-site covalently attached to puromycin. 

🐣 Because of ribosome cannot cleave amide bond, no further peptidyl transfer takes place and peptidyl-puromycin complex halts the proper function of ribosome.