Microbial Products

Definition
Microbial peptides are derived from microbes and act against host cells. Microbial peptides are usually all cyclic and they often co-occur with diketopiperazine units (DKPs) containing amino-acids found in the peptide. D-ammo-acids are usually present in some these peptides.

Discovery
This 34-residue anionic amphiphatic antimicrobial peptide named dermaseptin was purified from amphibian skin ¹. Mor et al., (1994) have reported that individual dermaseptins have distinct spectra of anti-microbial activity. Some of them synergize strongly, with certain combinations showing a 100-fold increase in antibiotic activity over the activity of single peptides ².  Another microbial peptide PvMSP - 1 peptide 19 (378 - 397) fragment of malaria Plasmodium vivax (PvMSP-1) is merozoite surface antigen, T-helper epitope. This T-cell epitope is present in the merozoite surface protein-1 of PvMSP-1 ³. Ovine antimicrobial anionic peptide, is the surfactant-associated ovine antimicrobial anionic peptide (AP) plays a role in protection of the respiratory tree ^{4, 5}.

Structural Characteristics
Microbial peptides are derived wholly, or in part, by enzymatically controlled condensations and ring expansions of diketopiperazine units (DKPs) because they are virtually all cyclic and they often co-occur with DKPs containing amino-acids found in the peptide ⁶.  Dermaseptins peptides possess a common preproregion and a variable C-terminal antimicrobial domain. Dermaseptins and related family members show extensive sequence identities with precursors of opioid peptides dermorphin, dermenkephalin, and deltorphins, as well as adenoregulin ⁷. Amino acid sequence of Dermaseptins-1 is ALWKTMLKKLGTMALHAGKAALGAAADTISQGTQMPF. Ovine pulmonary surfactant associated anionic peptides are smaller in size, opposite in charge, and are bactericidal in zinc saline solution ⁵. Hemoglobin, 3037a, Malaria FRET Substrate II sequence is DABCYL - GABA - Glu - Arg - Met - Phe - Leu - Ser - Phe - Pro – EDANS ⁸.

Mode of Action
Bacterial killing of ovine pulmonary surfactant appears to be due to a combination of pulmonary surfactant peptides and zinc in the serum. Ovine serum contains 15 mM zinc. The zinc is bound loosely to serum proteins, particularly albumin. The mechanisms of cell death are related to the pH of surfactant containing anionic peptide or involve a metabolic event by which the anionic peptide and zinc are taken up by the bacterial cell ⁵.  The NH₂-terminal α-helical domain 1-18 of dermaseptin has been shown to be responsible for antimicrobial activity. Dermaseptin is active against Leishmania mexicana. It stimulates microbicidal activities of polymorphonuclear leukocytes and stimulates production of reactive oxygen species, release of myeloperoxidase, and a rapid and transient elevation of cytosolic-free calcium concentration and phospholipase D activity in neutrophils ⁹. 

Functions

Bactericidal activity: Ovine pulmonary surfactant kills several gram-positive and gram-negative bacteria in zinc saline solutions ⁵.

Dermaseptin: Possesses highly potent antimicrobial activity against pathogenic fungi at micromolar concentration and is not hemolytic for erythrocytes. Dermaseptin-1 has the ability to reduce the infectivity of channel catfish virus (CCV) and frog virus 3 (FV3). Dermaseptin-4 has potent spermicidal activities ⁹.

Malaria CSP (334 - 342): This is amino acids 334 to 342 fragment of malaria CSP derived from malaria circumsporozoite protein. It is commonly used as a control peptide for melanoma vaccine studies ¹⁰.

PvMSP - 1 peptide 19 (378 - 397): It induces lymphoproliferative responses in cells from individuals with previous P. vivax infections ³.

Hemoglobin, 3037a, Malaria FRET Substrate II: This peptide was used to characterize the molecular mechanism underlying Hb degradation by plasmepsin II (PM II). N-terminal (GABA) extension results in higher maximal velocity and dramatic concentration-dependent substrate inhibition ⁸.

PvMSP-1 T-cell epitopes: Linear-peptide chimeras containing the promiscuous PvMSP-1 T-cell epitopes, synthesized in tandem with the Plasmodium falciparum immunodominant circumsporozoite protein (CSP) B-cell epitope, induced high specific antibody titers, cytokine production, long-lasting immune responses, and immunoglobulin G isotype class switching in BALB/c mice. The anti-peptide antibodies generated to the CSP B-cell epitope inhibited the invasion of P. falciparum sporozoites into human hepatocytes. These data and the simplicity of design of the chimeric constructs highlight the potential of multimeric, multistage, and multispecies linear-peptide chimeras containing parasite promiscuous T-cell epitopes for malaria vaccine development ³.

References

1. Mor A, Nguyen VH, Delfour A, Migliore-Samour D, Nicolas P (1991). Isolation, amino acid sequence, and synthesis of dermaseptin, a novel antimicrobial peptide of amphibian skin. Biochemistry, 30(36): 8824-8830.   
2. Mor A, Hani K, Nicolas P (1994). The vertebrate peptide antibiotics dermaseptins have overlapping structural features but target specific microorganisms. Journal of Biological Chemistry, 269(50):31635-31641.
3. Caro-Aguilar I, Rodríguez A, Calvo-Calle JM, Guzmán F, De la Vega P, Patarroyo ME, Galinski MR, Moreno A (2002). Plasmodium vivax Promiscuous T-Helper epitopes defined and evaluated as linear peptide chimera immunogens. Infect. Immun., 70:3479-3492.
4. Brogden KA, Ackermann M, Huttner KM (1998). Detection of anionic antimicrobial peptides in ovine bronchoalveolar lavage fluid and respiratory epithelium. Infection and Immunity., 66(12):5948-5954.
5. Brogden K (1996). Isolation of an ovine pulmonary surfactant-associated anionic      peptide bactericidal for Pasteurella haemolytica. PNAS., 93:412-416.
6. Bycroft BW (1969). Structural Relationships in Microbial Peptides. Nature, 224:595-597.
7. Amiche M, Seon AA, Pierre TN, Nicolas P  (1999). The dermaseptin precursors: a protein family with a common preproregion and a variable C-terminal antimicrobial domain. FEBS Letters., 456(3):352-356.
8. Istvan E, Goldberet DE (2005). Distal substrate interactions enhance plasmepsin activity. J. Biol. Chem., 280: 6890-6896.
9. Yamshchikov GV, Mullins DW, Chang CC, Ogino T, Thompson L, Presley J, Galavotti H, Aquila W, Deacon D, Ross W, Patterson JW, Engelhard VH, Ferrone S, Slingluff CL Jr (2005).  Sequential immune escape and shifting of T cell responses in a long-term survivor of melanoma. J. Immunol., 174(11):6863-6871.