The regulation of synthesis and secretion of many bacterial toxinsistightly controlled by regulatory elements that are sensitive toenvironmentalsignals. For example, the production of diphtheria toxin is totallyrepressedby the availability of adequate amounts of iron in the medium forbacterialgrowth. Only under conditions of limiting amounts of iron in the growthmedium does toxin production become derepressed. The expression ofcholeratoxin and related virulence factors (adhesins) is controlled byenvironmentalosmolarity and temperature. In , induction ofdifferentvirulence components is staggered, such that attachment factors areproducedinitially to establish the infection, and toxins are synthesized andreleasedlater to counter the host defenses and promote bacterial survival.
There are numerous protein factors required for events like the binding to the small ribosomal subunit, binding to the charged initiator tRNA (in eukaryotes: met-tRNA), recognition of the 5' cap, and recognition of the 3' poly-A tail (eukaryotic initiation involves both the 5' and 3' end of the mRNA and its folding).
Exotoxinsare usually secreted by bacteria and act at a site removed frombacterial growth. However, in some cases, exotoxins are only releasedbylysis of the bacterial cell. Exotoxins are usually proteins, minimallypolypeptides, that act enzymatically or through direct action with hostcells and stimulate a variety of host responses. Most exotoxins act attissue sites remote from the original point of bacterial invasionor growth. However, some bacterial exotoxins act at the site ofpathogen colonizationand may play a role in invasion.
Bacterial protein toxins are strongly antigenic., specificantibody neutralizes the toxicity of these bacterialexotoxins (antitoxin). However, specific antitoxin may not fully inhibit theiractivity. This suggests that the antigenic determinant of thetoxin may be distinct from the active portion of theproteinmolecule. The degree of neutralization of the active site may dependon the distance from the antigenic site on the molecule. However, sincethe toxin is fully neutralized , this suggests that other hostfactorsmust play a role in toxin neutralization in nature.
Translation is then the process by which an RNA base sequence is used to directed the synthesis of a specific polypeptide with a specific amino acid sequence.
The large subunit then displaces the initiation factors and facilitates the correct alignment of the initiation tRNA on the P site of the ribosome.
(Type I and type II synthetases, respectively.) Even if the amino acid is initially attached to the 2' OH, it is the 3' OH form that is used in protein synthesis.* This charged tRNA is now ready to take part in translation.
There are a variety of ways that toxin subunits may be synthesizedandarranged: A + B indicates that the toxin is synthesized andsecretedas two separate protein subunits that interact at the target cellsurface;A-Bor A-5B indicates that the A and B subunits are synthesizedseparately,but associated by noncovalent bonds during secretion and binding totheirtarget; 5B indicates that the binding domain of the protein iscomposedof 5 identical subunits. A/B denotes a toxin synthesized as asinglepolypeptide, divided into A and B domains that may be separated byproteolyticcleavage.
At a chemical level, there are two main types ofbacterial toxins,lipopolysaccharides,which are associated with the cell wall of Gram-negative bacteria, andproteins,which are released from bacterial cells and may act at tissue sitesremovedfrom the site of bacterial growth. The cell-associated toxinsare referred to as endotoxinsand the extracellulardiffusible toxins are referred to as exotoxins.
This Concept Map, created with IHMC CmapTools, has information related to: Protein synthesis, messengerRNA is complementary to one gene, mRNA processing produces an exons-only messengerRNA, messengerRNA during translation, binds to mRNA binding site, Transcription process produces a complementary messengerRNA, peptide chain synthesize into protein, anti-codon 1 to1 relation amino acid, ribosomalRNA is a type of RNA, messengerRNA introns removed and exons are spliced in mRNA processing, messengerRNA is a type of RNA, DNA (Deoxyribonucleic Acid) for protein creation, going through Transcription process, transferRNA is a type of RNA, gene is a protein-synthesis data unit in the DNA (Deoxyribonucleic Acid), chromosome the most dense package of DNA (Deoxyribonucleic Acid), mRNA binding site is a part of small subunit, anti-codon is a part of transferRNA, P-site is a part of large subunit, amino acid anti-codon, amino acid is the building block of peptide chain, ribosome is built from ribosomalRNA, transferRNA binds to amino acid
The best known and studied bacterial toxin is the diphtheria toxin,produced by . Diphtheria toxin is abacterialexotoxin of the A/B prototype. It is produced as single polypeptidechainwith a molecular weight of 60,000 daltons. The function of the proteinis distinguishable into two parts: subunit A, with a m.w. of 21,000daltons,contains the enzymatic activity for inhibition of elongation factor-2involvedin host protein synthesis; subunit B, with a m.w. of 39,000 daltons, isresponsible for binding to the membrane of a susceptible host cell. TheB subunit possesses a region T (translocation) domain which insertsinto the endosome membrane thus securing the release of the enzymaticcomponent into the cytoplasm.