Cecropin family | |||||||||
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Identifiers | |||||||||
Symbol | Cecropin | ||||||||
Pfam | PF00272 | ||||||||
InterPro | IPR000875 | ||||||||
PROSITE | PDOC00241 | ||||||||
SCOP2 | 1f0d / SCOPe / SUPFAM | ||||||||
TCDB | 1.C.17 | ||||||||
OPM superfamily | 151 | ||||||||
OPM protein | 1d9j | ||||||||
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Cecropins are antimicrobial peptides. [1] [2] They were first isolated from the hemolymph of Hyalophora cecropia , whence the term cecropin was derived. Cecropins lyse bacterial cell membranes; they also inhibit proline uptake and cause leaky membranes.
Cecropins [3] [4] [5] constitute a main part of the innate immune system of insects. Cecropins are small proteins anywhere from 31 - 37 amino acids long and are active against both gram-positive and gram-negative bacteria. Cecropins isolated from insects other than Hyalophora cecropia (Cecropia moth) have been given various names, such as bactericidin, lepidopterin, and sarcotoxin. All of these peptides are structurally related.
Members include:
A derivative of Cecropin B is an anticancer polypeptide(L). Structure consists of mainly alpha helixes, determined by solution NMR. Protein molecular weight = 4203.4g/mol. [9]
Some of the cecropins (e.g. cecropin A, and cecropin B) have anticancer properties and are called anticancer peptides (ACPs). [6] : 3 Hybrid ACPs based on Cecropin A have been studied for anticancer properties. [6] : 7.1
Anticancer activities of cecropin B, cecropin P1, and Shiva-1 were first demonstrated with in vitro studies of mammalian leukemia and lymphoma cell lines, where cells were sensitive to peptide concentrations on the order of 10−6 M. [10] Two multidrug-resistant breast and ovarian cancer cell lines also showed sensitivity to the peptides. [10] Further, peptide anticancer activity is reported as being complete within one hour of treatment. [10] In vivo studies of murine ascitic colon adenocarcinoma cells showed a similar trend, where mice treated with cecropin B exhibited increased survival time compared to untreated mice. [10] Structural studies of cecropin B and its derivative cecropin B3 showed that anticancer activity arises from the ability of the antimicrobial peptides to form pores in stomach carcinoma cell membranes. [6] [11] Measuring electrical currents on cell surfaces showed that cecropin B, but not cecropin B3, induces outward currents indicative of pore formation. [11] Further, cecropin B3 lacks an amphipathic group present in cecropin B, suggesting that this amphipathic group is necessary for cecropin B to insert into cell membranes and form pores. [11] Cecropin B has strong activity on bacteria as well as cancer cells, while B3 has little effect on either. [11] Notably, another derivative, cecropin B1, has two amphipathic regions and exhibits potent activity against human leukemia cell lines at concentrations that do not affect normal fibroblasts or red blood cells. [6]
Different cecropins act on different types of human cancer cells and show activity at concentrations that are not harmful to normal cells. For example, a recent study of Cecropins A and B demonstrated strongly cytotoxic activity against four bladder cancer cell lines, while benign murine and human fibroblasts were not susceptible to Cecropin A or B. [12] Cecropins from many insect species have been shown to be active against a diverse range of human cancer cell lines. For example, Mdcec, a cecropin originating from the common housefly, has been shown to have an antiproliferative effect on human hepatocellular carcinoma cell line BEL-7402 without affecting normal liver cells. [13] Flow cytometry and RT-PCR experiments revealed that treatment with Mdcec increased expression of pro-apoptotic genes such as caspase-3, leading to cancer cell death. [13] These same genes did not show significant expression changes in healthy cells upon treatment with Mdcec. [13] This suggests a degree of specificity which has promise for development of novel cancer therapies.
Further supporting therapeutic efficacy, a study of cecropin A affirmed that cecropin A selectively lyses leukemia cells while exerting little effect on normal lymphocytes. [14] In the same study, chemotherapy drugs cytarabine and 5-fluorouracil synergize with cecropin A in vitro to enhance cytotoxic effects on leukemia cells. [14] This indicates potential for therapeutic application of antimicrobial peptides in cancer, where treatment with cecropins could lower the required dosage of chemotherapy drugs, reducing undesirable side effects. Major challenges to the use of cecropins as cancer therapeutics are delivery of the peptides to tumor cells. [6] [15] Repeated administration of peptides is necessary to maintain systemic levels of cecropins at sufficient concentrations for anti-cancer activity. [6] [15] This need for repeated administration complicates potential treatment plans. One proposed alternative suggests use of gene therapy to introduce cecropin genes into cancer cells. [6] [15] A study in which cecropin genes were expressed in a human bladder carcinoma cell line showed that tumor cells bearing cecropin genes have reduced tumorigenicity, up to complete loss of tumorigenicity in some cell clones. [15]
More recent studies have identified new cecropins, which may be prove useful in development of cancer therapeutics. For example, genome and transcriptome analyses of the spruce budworm Choristoneura fumiferana resulted in identification of novel cecropins which differ from previously characterized cecropins in that they are negatively charged, rather than positively charged. [16] A BH3-like motif (amino acid sequence G-[KQR]-[HKQNR]-[IV]-[KQR]) is present in both anionic and cationic cecropins, and analysis suggests that this motif may interact with Bcl-2, a protein implicated in apoptosis. [16] Further study of cecropin structure and anticancer properties may inform design of novel cancer therapeutics.
Cecropin A can destroy planktonic and sessile biofilm-forming uropathogenic E. coli (UPEC) cells, either alone or when combined with the antibiotic nalidixic acid, synergistically clearing infection in vivo (in the insect host Galleria mellonella ) without off-target cytotoxicity. The multi-target mechanism of action involves outer membrane permeabilization followed by biofilm disruption triggered by the inhibition of efflux pump activity and interactions with extracellular and intracellular nucleic acids. [17]
Pardaxin is a peptide produced by the Red Sea sole and the Pacific Peacock sole that is used as a shark repellent. It causes lysis of mammalian and bacterial cells, similar to melittin.
Lactoferrin (LF), also known as lactotransferrin (LTF), is a multifunctional protein of the transferrin family. Lactoferrin is a globular glycoprotein with a molecular mass of about 80 kDa that is widely represented in various secretory fluids, such as milk, saliva, tears, and nasal secretions. Lactoferrin is also present in secondary granules of PMNs and is secreted by some acinar cells. Lactoferrin can be purified from milk or produced recombinantly. Human colostrum has the highest concentration, followed by human milk, then cow milk (150 mg/L).
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 signaling 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 antimicrobials 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.
An amphiphile, or amphipath, is a chemical compound possessing both hydrophilic and lipophilic (fat-loving) properties. Such a compound is called amphiphilic or amphipathic. Amphiphilic compounds include surfactants. The phospholipid amphiphiles are the major structural component of cell membranes.
Dermcidin is a protein with 110 amino acids that in humans is encoded by the DCD gene. The full-length protein produces derived peptides as proteolysis-inducing factor (PIF) and other anti-microbial peptides, secreted by human eccrine sweat glands onto the skin as a part of the innate host defense of the immune system. PIF is involved in muscular proteolysis.
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.
Cell-penetrating peptides (CPPs) are short peptides that facilitate cellular intake and uptake of molecules ranging from nanosize particles to small chemical compounds to large fragments of DNA. The "cargo" is associated with the peptides either through chemical linkage via covalent bonds or through non-covalent interactions.
Alpha defensins are a family of mammalian defensin peptides of the alpha subfamily. In mammals they are also known as cryptdins and are produced within the small bowel. Cryptdin is a portmanteau of crypt and defensin.
Plant defensins are a family of primitive, highly stable, cysteine-rich defensins found in plants that function to defend them against pathogens and parasites. Defensins are integral components of the innate immune system and belong to the ancient superfamily of antimicrobial peptides (AMPs). AMPs are also known as host defense peptides (HDPs), and they are thought to have diverged about 1.4 billion years ago before the evolution of prokaryotes and eukaryotes. They are ubiquitous in almost all plant species, functionally diverse, and their primary structure varies significantly from one species to the next, except for a few cysteine residues, which stabilize the protein structure through disulfide bond formation. Plant defensins usually have a net positive charge due to the abundance of cationic amino acids and are generally divided into two classes. Those in the class II category contain a C-terminal pro-peptide domain of approximately 33 amino acids and are targeted to the vacuole, while the class I defensins lack this domain and mature in the cell wall. Unlike their class I counterparts, class II plant defensins are relatively smaller, and their acidic C-terminal prodomain is hypothesized to contribute to their vacuolar targeting. The first plant defensins were discovered in barley and wheat in 1990 and were initially designated as γ-thionins. In 1995, the name was changed to 'plant defensin' when it was identified that they are evolutionarily unrelated to other thionins and were more similar to defensins from insects and mammals.
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.
Pseudin is a peptide derived from Pseudis paradoxa. Pseudins have some antimicrobial function.
FDC-SP or follicular dendritic cell-secreted protein, is a small, secreted protein, located on chromosome 4 in humans. It is thought to play an immune role in the junctional epithelium at the gingival crevice in the human mouth. It is very similar in structure to statherin, a protein contained in saliva.
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.
Anticancer genes exhibit a preferential ability to kill cancer cells while leaving healthy cells unharmed. This phenomenon is achieved through various processes such as apoptosis following a mitotic catastrophe, necrosis, and autophagy. In the late 1990s, extensive research in the field of cancer cells led to the discovery of anticancer genes. Currently, 291 anticancer genes have been identified. The deregulation of these genes due to base substitutions leading to insertions, deletions, or alterations in missense amino acids can cause frameshifts, thereby altering the protein. A change in gene copy number or rearrangements is also essential for deregulating these genes. The loss or alteration of these anticancer genes due to mutations or rearrangements may lead to the development of cancer.
Attacin is a glycine-rich protein of about 20 kDa belonging to the group of antimicrobial peptides (AMP). It is active against Gram-negative bacteria.
Hans Gustaf Boman (1924-2008) was a Swedish microbiologist with a special focus on innate immunity. Boman was born on 16 August 1924 in Engelbrekt Parish, Stockholm, Sweden, and died on 3 December 2008. Boman's pioneering research on insect immunity formed the basis for the Nobel Prize in Physiology or Medicine that was awarded to Jules Hoffman in 2011.
Drosocin is a 19-residue long antimicrobial peptide (AMP) of flies first isolated in the fruit fly Drosophila melanogaster, and later shown to be conserved throughout the genus Drosophila. Drosocin is regulated by the NF-κB Imd signalling pathway in the fly.
The Imd pathway is a broadly-conserved NF-κB immune signalling pathway of insects and some arthropods that regulates a potent antibacterial defence response. The pathway is named after the discovery of a mutation causing severe immune deficiency. The Imd pathway was first discovered in 1995 using Drosophila fruit flies by Bruno Lemaitre and colleagues, who also later discovered that the Drosophila Toll gene regulated defence against Gram-positive bacteria and fungi. Together the Toll and Imd pathways have formed a paradigm of insect immune signalling; as of September 2, 2019, these two landmark discovery papers have been cited collectively over 5000 times since publication on Google Scholar.
Halovir refers to a multi-analogue compound belonging to a group of oligopeptides designated as lipopeptaibols which have membrane-modifying capacity and are fungal in origin. These peptides display interesting microheterogeneity; slight variation in encoding amino acids gives rise to a mixture of closely related analogues and have been shown to have antibacterial/antiviral properties.