1. Common structural properties specifically found in the CSalphabeta-type antimicrobial peptides in nematodes and mollusks: evidence for the same evolutionary origin?
Hong Zhang, Yusuke Kato Dev Comp Immunol. 2003 Jun-Jul;27(6-7):499-503. doi: 10.1016/s0145-305x(02)00141-6.
The structural properties of the Ascaris suum antibacterial factor (ASABF)-type antimicrobial peptides, isolated from nematodes, were compared with the CSalphabeta-type antimicrobial peptides found in other organisms. The spacing of the half-cystine residues, cysteine pairings, and organization of the precursor were different from the 'classical' CSalphabeta-type antimicrobial peptides, such as drosomycin and plant defensins, and identical only to the MGD and myticin in mollusks. In addition, ABF-5, a member of the ASABF-type antimicrobial peptides in Caenorhabditis elegans, is predicted to contain a basic mature region and an acidic pro-region, similar to MGD and myticin. These results suggest that the ASABF-type antimicrobial peptides, MGD and myticin are similar in their structure.
2. Mussel defensins are synthesised and processed in granulocytes then released into the plasma after bacterial challenge
G Mitta, F Vandenbulcke, F Hubert, P Roch J Cell Sci. 1999 Dec;112 ( Pt 23):4233-42. doi: 10.1242/jcs.112.23.4233.
MGD1 (Mytilus galloprovincialis defensin 1), a new member of the arthropod defensin family, is a 4 kDa antibacterial peptide previously isolated from the plasma of Mediterranean mussels. We report here the presence of MGD1 in the organelle-rich fraction of hemocytes and the cDNA sequence corresponding to MGD1 and one new isoform mRNA: MGD2. Sequence analysis indicated that MGDs are synthesised as precursors consisting of a putative signal peptide of 21 residues, the active peptide of 39 amino acids and a 21 residue carboxyl-terminal extension, rich in acidic amino acids. Localisation of the transcripts by northern blot revealed that the precursors are abundantly expressed in hemocytes. Immunocytochemistry at both the optical and ultrastructural levels showed that defensins (i) are predominantly located in vesicles of a granulocyte subclass of hemocytes containing small granules, (ii) are also found in large clear granules of another granulocyte subclass, and (iii) that MGD immune reactivity existed in granular structures of enterocytes. Finally, we revealed that bacterial challenge triggered a plasmatic increase of MGD1 concentration and gave evidence of the simultaneous release of the peptides from the hemocytes.
