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Tachyplesin is an antimicrobial peptide isolated from the horseshoe crab. It has a molecular weight of 2.36 kDa and the amino acid sequence KWCFRVCYRGICYRRCR. [1]
Horseshoe crabs are marine and brackish water arthropods of the family Limulidae and the only living members of the order Xiphosura. Despite their name, they are not true crabs or crustaceans: they are chelicerates, most closely related to arachnids, such as spiders and scorpions.
Defensins are small cysteine-rich cationic proteins across cellular life, including vertebrate and invertebrate animals, plants, and fungi. They are host defense peptides, with members displaying either direct antimicrobial activity, immune signalling activities, or both. They are variously active against bacteria, fungi and many enveloped and nonenveloped viruses. They are typically 18-45 amino acids in length, with three or four highly conserved disulphide bonds.
Antimicrobial peptides (AMPs), also called host defence peptides (HDPs) are part of the innate immune response found among all classes of life. Fundamental differences exist between prokaryotic and eukaryotic cells that may represent targets for antimicrobial peptides. These peptides are potent, broad spectrum antibiotics which demonstrate potential as novel therapeutic agents. Antimicrobial peptides have been demonstrated to kill Gram negative and Gram positive bacteria, enveloped viruses, fungi and even transformed or cancerous cells. Unlike the majority of conventional antibiotics it appears that antimicrobial peptides frequently destabilize biological membranes, can form transmembrane channels, and may also have the ability to enhance immunity by functioning as immunomodulators.
A hemocyte is a cell that plays a role in the immune system of invertebrates. It is found within the hemolymph. Hemocytes are phagocytes of invertebrates.
Cathelicidin antimicrobial peptide (CAMP) is a polypeptide that is primarily stored in the lysosomes of macrophages and polymorphonuclear leukocytes (PMNs); in humans, the CAMP gene encodes the peptide precursor CAP-18, which is processed by proteinase 3-mediated extracellular cleavage into the active form LL-37. LL-37 is the only peptide in the Cathelicidin family found in the human body.
The minimum bactericidal concentration (MBC) is the lowest concentration of an antibacterial agent required to kill a particular bacterium. It can be determined from broth dilution minimum inhibitory concentration (MIC) tests by subculturing to agar plates that do not contain the test agent. The MBC is identified by determining the lowest concentration of antibacterial agent that reduces the viability of the initial bacterial inoculum by ≥99.9%. The MBC is complementary to the MIC; whereas the MIC test demonstrates the lowest level of antimicrobial agent that inhibits growth, the MBC demonstrates the lowest level of antimicrobial agent that results in microbial death. This means that even if a particular MIC shows inhibition, plating the bacteria onto agar might still result in organism proliferation because the antimicrobial did not cause death. Antibacterial agents are usually regarded as bactericidal if the MBC is no more than four times the MIC. Because the MBC test uses colony-forming units as a proxy measure of bacterial viability, it can be confounded by antibacterial agents which cause aggregation of bacterial cells. Examples of antibacterial agents which do this include flavonoids and peptides.
Beta defensins are a family of vertebrate defensins. The beta defensins are antimicrobial peptides implicated in the resistance of epithelial surfaces to microbial colonization.
Arthropod defensins are a family defensin proteins found in mollusks, insects, and arachnids. These cysteine-rich antibacterial peptides are primarily active against Gram-positive bacteria and fungi in vitro. However Drosophila fruit flies mutant for the fly defensin were more susceptible to infection by the Gram-negative bacteria Providencia burhodogranariea, and resisted infection against Gram-positive bacteria like wild-type flies. It remains to be seen how in vitro activity relates to in vivo function. Mutants for the defensin-like antimicrobial peptide Drosomycin were more susceptible to fungi, validating a role for defensin-like peptides in anti-fungal defence.
Protegrins are small peptides containing 16-18 amino acid residues. Protegrins were first discovered in porcine leukocytes and were found to have antimicrobial activity against bacteria, fungi, and some enveloped viruses. The amino acid composition of protegrins contains six positively charged arginine residues and four cysteine residues. Their secondary structure is classified as cysteine-rich β-sheet antimicrobial peptides, AMPs, that display limited sequence similarity to certain defensins and tachyplesins. In solution, the peptides fold to form an anti-parallel β-strand with the structure stabilized by two cysteine bridges formed among the four cysteine residues. Recent studies suggest that protegrins can bind to lipopolysaccharide, a property that may help them to insert into the membranes of gram-negative bacteria and permeabilize them.
Adrenorphin, also sometimes referred to as metorphamide, is an endogenous, C-terminally amidated, opioid octapeptide (Tyr-Gly-Gly-Phe-Met-Arg-Arg-Val-NH2, YGGFMRRV-NH2) that is produced from proteolytic cleavage of proenkephalin A and is widely distributed throughout the mammalian brain. It was named based on the fact that it was originally detected in human phaeochromocytoma tumour derived from the adrenal medulla, and was subsequently found in normal human and bovine adrenal medulla as well. Adrenorphin exhibits potent opioid activity, acting as a balanced μ- and κ-opioid receptor agonist while having no effects on δ-opioid receptors. It possesses analgesic and respiratory depressive properties.
Coagulin is a gel-forming protein of hemolymph that hinders the spread of invaders by immobilising them. It is produced in the coagulogen form before being cleaved into the active form. In human medicine, coagulation of coagulin is the basis of detection of bacterial endotoxin in the LAL test for parenteral medications.
Tachystatins are antimicrobial chitin-binding peptides from Japanese horseshoe crab. Amino acid residues Tyr(14) and Arg(17) in Tachystatin B are thought to be the essential residues for chitin binding. These small proteins contain a cysteine-stabilised triple-stranded beta-sheet with an inhibitor cystine knot motif and show features common to membrane-interactive peptides. Tachystatin A is thought to have an antimicrobial activity similar to defensins.
Arenicins are a group of antimicrobial peptides being studied to combat Gram-negative bacteria.
Limulus clotting factor overbar C is an enzyme. This enzyme catalyses the following chemical reaction
Limulus clotting factor B is an enzyme. This enzyme catalyses the following chemical reaction
Limulus clotting enzyme is an enzyme. This enzyme catalyses the following chemical reaction
Halocidin is an antimicrobial peptide isolated from the Halocynthia aurantium species of tunicate. In mouse models, derivative peptides have shown efficacy in the treatment of fungicidal resistant Candida Albacans when used as a mouthwash additive.
Halocyaminess are antibiotic peptides isolated from the ascidian Halocynthia roretzi.
Clavanin B is an alpha-helical antimicrobial peptide isolated from Styela clava.
Spooky toxin (SsTx) is a small peptide neurotoxin. It is found in the venom of Chinese red-headed centipedes, also known as golden head centipedes. It is originally composed of 76 amino acids, with a molecular weight of 6017.5 Daltons, but loses the first 23 residues and becomes 53 residues long. SsTx is currently thought to be unique to Scolopendra subspinipes mutilans.
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