title: Styelin D, an extensively modified antimicrobial peptide from ascidian hemocytes.
abstract: We isolated styelin D, a 32-residue, C-terminally amidated antimicrobial peptide, from the blood cells (hemocytes) of the solitary ascidian, Styela clava. Styelin D had remarkably extensive post-translational modifications, containing two novel amino acids, dihydroxyarginine and dihydroxylysine, and two distinctly unusual ones, 6-bromotryptophan and 3,4-dihydroxyphenylalanine. In addition, the peptide exhibited microheterogeneity because of differential mono- and dihydroxylation of several lysine residues. The primary sequence of one variant was: GW(*)LR(**)K(**)AAK(**)SVGK(**)FY(*)Y(*)K(**)HK(*)Y(*) Y(*)IK(*)AAWQIG KHAL-NH(2), where W(*) is 6-bromotryptophan, R(**) is dihydroxyarginine, Y(*) is 3,4-dihydroxyphenylalanine, K(*) is 5-hydroxylysine, and K(**) is dihydroxylysine. Styelin D exhibited activity against Gram-negative and Gram-positive bacteria, and this activity was retained in 200 mm NaCl. The role of the extensive modifications may be to preserve activity at low pH and/or high salinity because, under these conditions, the native peptide was considerably more active against the Gram-positive bacterial strains than its unmodified synthetic analogue. The peptide was also hemolytic and quite cytotoxic to eukaryotic cells. These broad ranging activities, combined with its relative abundance in ascidian hemocytes, suggest that styelin D plays a significant role in the innate immune mechanisms of S. clava.
authors.affiliation: Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0204, USA. swtaylor@ucsd.edu
authors.forename: S W
authors.initials: SW
authors.lastname: Taylor
authors.forename: A G
authors.initials: AG
authors.lastname: Craig
authors.forename: W H
authors.initials: WH
authors.lastname: Fischer
authors.forename: M
authors.initials: M
authors.lastname: Park
authors.forename: R I
authors.initials: RI
authors.lastname: Lehrer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology; D023181:Antimicrobial Cationic Peptides; D002463:Cell Membrane Permeability / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D004295:Dihydroxyphenylalanine / Q000032:analysis; D004926:Escherichia coli / Q000187:drug effects / Q000502:physiology; D008401:Gas Chromatography-Mass Spectrometry; D006434:Hemocytes / Q000737:chemistry*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D011506:Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology; D014364:Tryptophan / Q000031:analogs & derivatives / Q000032:analysis; D014561:Urochordata
chemical_list: C110059:6-bromotryptophan; D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D010446:Peptide Fragments; D011506:Proteins; C107549:styelin D; D004295:Dihydroxyphenylalanine; D014364:Tryptophan