A tetrapeptide is a peptide , classified as an oligopeptide , because it consists of only four amino acids linked by peptide bonds . Many tetrapeptides are pharmacologically active, often showing affinity and specificity for various receptors in protein–protein signaling. Existing in nature are both linear and cyclic tetrapeptides (CTPs), the latter of which mimic the protein reverse turn often present on the surface of proteins and druggable targets.   The tetrapeptide is cycled by a fourth peptide bond or by other covalent bonds .can be done .
Examples of tetrapeptides are:
- Tuftsin ( L -threonyl- L -lysyl- L -prolyl- L – arginine) is a peptide primarily related to immune system function.
- Riggin (glycyl -L- glutaminyl -L- prolyl -L- arginine) is a tetrapeptide with functions similar to tuftsin.
- Postin (Lys-Pro-Pro-Arg) is the N-terminal tetrapeptide of cystatin C and is an antagonist of tuftsin.
- Endomorphin-1 (H-Tyr-Pro-Trp-Phe-NH 2 ) and endomorphin-2 (H-Tyr-Pro-Phe-Phe-NH 2 ) are peptide amides that have the highest known affinity and specificity for the μ opioid receptor . ,
- Morphiceptin (H-Tyr-Pro-Phe-Pro-NH 2 ) is a casomorphin peptide that is isolated from β- casein .
- Gluten exorphins A4 (H-Gly-Tyr-Tyr-Pro-OH) and B4 (H-Tyr-Gly-Gly-Trp-OH) are peptides isolated from gluten .
- Tyrosine-MIF-1 (H-Tyr-Pro-Leu-Gly-NH 2 ) is an endogenous opioid modulator.
- Tetragastrin ( N -((phenylmethoxy)carbonyl) -L – tryptophyl-L-methionyl-L-aspartyl – L – phenylalaninamide ) is the C-terminal tetrapeptide of gastrin . It is the shortest peptide fragment of gastrin that has physiological and pharmacological activity similar to that of gastrin.
- Kentsin (H-Thr-Pro-Arg-Lys-OH) is a contraceptive peptide first isolated from female hamsters .
- Achatin-I (glycyl-phenylalanyl-alanyl-aspartic acid) is a neuroexcitatory tetrapeptide from the giant African snail ( Achatina fulica ) .
- Tentoxin (cyclo( N -methyl- L-alanyl-L – leucyl – N – methyl – trans – dehydrophenyl -alanyl-glycyl)) is a natural cyclic tetrapeptide produced by the phytopathogenic fungus from the genus Alternaria .
- Rapastinel (H-Thr-Pro-Pro-Thr-NH 2 ) is a partial agonist of the NMDA receptor .
- The HC-toxin , cyclo (d-pro-l-ala-d-ala-l-ao), where aeo is 2-amino-8-oxo-9,10-epoxy decanoic acid, is a virulence factor for the fungus Cochliobolus. Carbonum on its host, maize .
- Elamipretide , (D-Arg-dimethylTyr-Lys-Phe-NH2) is a drug candidate that targets mitochondria .
Peptide Bond Covalent Characteristics
There are some characteristics of covalent peptide bond, which are described below-
Peptide bonds are strong, rigid and planar. The peptide bond is not flexible and free rotation about this bond becomes restricted. This bond has some double bond character due to the sharing of unpaired electrons, which is one of the main characteristics of covalent linkages. The peptide bond also has a partial positive charge due to the presence of polar hydrogen atoms of the amino group and a partial negative charge due to the presence of polar oxygen atoms from the carboxylic acid group. Due to resonance stabilization, the peptide bond remains basically unreactive under physiological conditions, even as they are less reactive than their nearly identical compounds, esters.
Frequently Asked Questions For Tetrapeptide
How can a peptide bond be broken?
Answer: Peptide bonds can be broken by hydrolysis. The amide type linkage is hydrolyzed by adding water and gives two component amino acid residues.
Are peptide bonds strong or weak ?
Answer: Peptide bond is an example of strong covalent bond with high bond dissociation energy.
Why is a peptide bond a covalent bond?
Answer: The peptide bond is formed due to the sharing of electrons between carbon and nitrogen and is one of the most important characteristics of a covalent bond.