Involvement of mytilins in mussel antimicrobial defense.
Four cationic peptides were purified from mussel (Mytilus galloprovincialis) hemocytes. A combination of Edman degradation and mass spectrometry of plasma revealed (i) a previously characterized molecule, mytilin B (Charlet, M., Chernysh, S., Philippe, H., Hetrut, C., Hoffmann, J., and Bulet, P. (1996) J. Biol. Chem. 271, 21808-21813) and (ii) three new isoforms, mytilin C, D, and G1. The four molecules exhibited complementary antimicrobial properties. The cDNA sequence coding for the mytilin B precursor was obtained from a hemocyte cDNA library. This precursor contains a putative signal peptide of 22 residues, a processing peptide sequence of 34 amino acids, and a C-terminal extension of 48 residues rich in acidic residues. Distribution of mytilin B mRNA and of the corresponding peptide in various mussel tissues revealed that mytilins are synthesized and stored in a specific hemocyte subtype. Furthermore, in an experimental model of infection, we showed (i) a recruitment of hemocytes containing mytilins toward the injection site within hours following bacterial challenge, (ii) that mytilins probably play a prominent role in killing intracellular bacteria after phagocytosis, and (ii) later an increase of mytilin-like material occurred in the plasma suggesting a secondary systemic role.
Mitta
G
G
Défense et Résistance chez les Invertébrés Marins, IFREMER-CNRS, Université de Montpellier 2, cc 80, 34095 Montpellier, France.
Vandenbulcke
F
F
Hubert
F
F
Salzet
M
M
Roch
P
P
D000595:Amino Acid Sequence; D000818:Animals; D023181:Antimicrobial Cationic Peptides; D001483:Base Sequence; D049872:Bivalvia / Q000276:immunology / Q000382:microbiology*; D001798:Blood Proteins / Q000737:chemistry* / Q000502:physiology*; D015152:Blotting, Northern; D002465:Cell Movement; D002851:Chromatography, High Pressure Liquid; D018076:DNA, Complementary / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D015723:Gene Library; D006434:Hemocytes / Q000378:metabolism; D007150:Immunohistochemistry; D013058:Mass Spectrometry; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010455:Peptides; D010587:Phagocytosis; D012333:RNA, Messenger / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013997:Time Factors
D023181:Antimicrobial Cationic Peptides; D001798:Blood Proteins; D018076:DNA, Complementary; D010455:Peptides; D012333:RNA, Messenger; C408470:mytilin