Two novel 21-residue antimicrobial peptides, arenicin-1 and arenicin-2, exhibiting activity against Gram-positive and Gram-negative bacteria and fungi, were purified from coelomocytes of marine polychaeta Arenicola marina (lugworm) by preparative gel electrophoresis and RP-HPLC. Molecular masses (2758.3 and 2772.3 Da) and complete amino acid sequences (RWCVYAYVRVRGVLVRYRRCW and RWCVY-AYVRIRGVLVRYRRCW) 1 were determined for each isoform. Each arenicin has one disulfide bond (Cys3-Cys20). The total RNA was isolated from the lugworm coelomocytes, RT-PCR and cloning were performed, and cDNA was sequenced. A 202-residue preproarenicin contains a putative signal peptide (25 amino acids) and a long prodomain. Arenicins have no structure similarity to any previously identified antimicrobial peptides.
Among a variety of molecular factors of the plant innate immune system, small
proteins that transfer lipids and exhibit a broad spectrum of biological
activities are of particular interest. These are lipid transfer proteins
(LTPs). LTPs are interesting to researchers for three main features. The first
feature is the ability of plant LTPs to bind and transfer lipids, whereby these
proteins got their name and were combined into one class. The second feature is
that LTPs are defense proteins that are components of plant innate immunity.
The third feature is that LTPs constitute one of the most clinically important
classes of plant allergens. In this review, we summarize the available data on
the plant LTP structure, biological properties, diversity of functions,
mechanisms of action, and practical applications, emphasizing their role in
plant physiology and their significance in human life.
The membrane-active, cationic, β-hairpin peptide, arenicin, isolated from marine polychaeta Arenicola marina exhibits a broad spectrum of antimicrobial activity. The peptide in aqueous solution adopts the significantly twisted β-hairpin conformation without pronounced amphipathicity. To assess the mechanism of arenicin action, the spatial structure and backbone dynamics of the peptide in membrane-mimicking media and its pore-forming activity in planar lipid bilayers were studied. The spatial structure of the asymmetric arenicin dimer stabilized by parallel association of N-terminal strands of two β-hairpins was determined using triple-resonance nuclear magnetic resonance (NMR) spectroscopy in dodecylphosphocholine (DPC) micelles. Interaction of arenicin with micelles and its oligomerization significantly decreased the right-handed twist of the β-hairpin, increased its amphipathicity, and led to stabilization of the peptide backbone on a picosecond to nanosecond time scale. Relaxation enhancement induced by water-soluble (Mn(2+)) and lipid-soluble (16-doxylstearate) paramagnetic probes pointed to the dimer transmembrane arrangement. Qualitative NMR and circular dichroism study of arenicin-2 in mixed DPC/1,2-dioleoyl-sn-glycero-3-phosphoglycerol bicelles, sodium dodecyl sulfate micelles, and lipid vesicles confirmed that a similar dimeric assembly of the peptide was retained in membrane-mimicking systems containing negatively charged lipids and detergents. Arenicin-induced conductance was dependent on the lipid composition of the membrane. Arenicin low-conductivity pores were detected in the phosphatidylethanolamine-containing lipid mixture, whereas the high-conductivity pores were observed in an exclusively anionic lipid system. The measured conductivity levels agreed with the model in which arenicin antimicrobial activity was mediated by the formation of toroidal pores assembled of two, three, or four β-structural peptide dimers and lipid molecules. The structural transitions involved in arenicin membrane-disruptive action are discussed.
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