Marine Arthropods as a Source of Antimicrobial Peptides

Abstract

Peptide therapeutics play a key role in the development of new medical treatments. The traditional focus on endogenous peptides has shifted from first discovering other natural sources of these molecules, to later synthesizing those with unique bioactivities. This review provides concise information concerning antimicrobial peptides derived from marine crustaceans for the development of new therapeutics. Marine arthropods do not have an adaptive immune system, and therefore, they depend on the innate immune system to eliminate pathogens. In this context, antimicrobial peptides (AMPs) with unique characteristics are a pivotal part of the defense systems of these organisms. This review covers topics such as the diversity and distribution of peptides in marine arthropods (crustacea and chelicerata), with a focus on penaeid shrimps. The following aspects are covered: the defense system; classes of AMPs; molecular characteristics of AMPs; AMP synthesis; the role of penaeidins, anti-lipopolysaccharide factors, crustins, and stylicins against microorganisms; and the use of AMPs as therapeutic drugs. This review seeks to provide a useful compilation of the most recent information regarding AMPs from marine crustaceans, and describes the future potential applications of these molecules.

Keywords: AMP; antimicrobial peptides; crustaceans; defense system; drug; shrimp.

Figure 1

Alignment of five representative penaeidins belonging to subfamilies I and II, showing the conserved Cys-rich region with the characteristic six Cys residues forming three disulfide bonds. Cys residues of the disulfide loop are highlighted in yellow and highly conserved residues, in red.

Figure 2

Crystal structure of LVPen3 (PDB 1UEO) from P. vannamei, showing the typical amphipathic α−helix structure with three disulfide loops, and the cysteine and proline-rich sequences. Model built with Pymol V1.74.

Figure 3

Domains of the classic Penaeidin-I subfamily and the newest Penaeidin-II subfamily; SP = signal peptides, Cys RD = cysteine-rich domain, Prol RD = proline-rich domain, Ser RD = serine-rich domain. Adapted from [90].

Figure 4

(A) Structure of the classic penaeidins (PEN4c), showing conserved Pro-rich (blue) and Cys-rich (red) domains (model obtained with Swiss model); (B) New penaeidin (MjPen-II) family with the same conserved regions and the Ser-rich domain, proposed by An et al. [90].

Figure 5

Alignment of nine representative crustins from type I to type VII showing the conserved WAP domain with the characteristic eight Cys residues forming the four-disulfide core (4DSC). Cys residues of the disulfide core are highlighted in yellow and highly conserved residues, in red.

Figure 6

Structural features of the seven types and subtypes of crustins. Adapted from Molecular and Functional Diversity of Crustin-Like Genes in the Shrimp Penaeus vannamei [87]. (SP = signal peptide; CYS RD = Cys-rich domain; WAP = whey acidic protein; C-t = C-terminus; GLY RD = Gly-rich domain; S N-t = short N-terminus region; Arom = aromatic residues; SER/LEU RD = Ser/Leu-rich domain).

Figure 7

Structural differences between type IIa and IIb crustins. Adapted from [48].

Figure 8

Alignment of seven representative ALFs (A-G) showing the conserved lipopolysaccharide binding domain (LBD). The secondary structure is based on the crystal structure of ALF-Pm3 from P. monodon. Aromatic residues in LBD in green, cationic residues in LBD in blue, cysteine residues of disulfide loop highlighted in yellow, and highly conserved residues in red.

Figure 9

Crystal structure of ALF-Pm3 (PDB 2JOB) from P. monodon showing the typical α₁-β₁-β₂-β₃-α₂-α₃ structure and the disulfide loop. Model built with Pymol V1.74.

Figure 10

Schematic illustration of toroidal pore formation induced by the β-hairpin structures of tachyposin I.

Figure 11

The β-hairpin structures of tachyposin I and polyphemusin I are essential for their antimicrobial activity, amphipathicity, and hydrophobicity. (Tachyplesin I 1ma2_models and Polyphemusin-1) [183].

Figure 12

Defensin and tachycitin from the horseshoe crab Tachypleus tridentatus.