Hydramacin-1 in Action: Scrutinizing the Barnacle Model

Abstract

c Hydramacin-1 (HM1) from the metazoan Hydra exerts antimicrobial activity against a wide range of bacterial strains. Notably, HM1 induces the aggregation of bacterial cells, accompanied by precipitation. To date, the proposed mechanism of peptide-lipid interaction, termed the barnacle model, has not been described on the molecular level. Here, we show by biochemical and biophysical techniques that the lipid-peptide interactions of HM1 are initiated by electrostatic and hydrophobic effects, in particular, by tryptophan and neighboring polar amino acid residues that cause an interfacial localization of the peptide between two self-contained lipid bilayers. The high binding constants of HM1 upon lipid interaction are in the range of other potent antimicrobial peptides, e.g., magainin, and can be reasonably explained by two distinct epitopes on the surface of the peptide's global structure, which both contain SWT(K/R) motifs. The residues of this motif favor localization of the peptide in the head group region of phospholipid bilayers up to a penetration depth of 4 Å and a minor participation of the lipids' hydrocarbon regions. Our results expand the knowledge about the molecular modes of action antimicrobial peptides use to tackle their target cells. Furthermore, the aggregation of living bacteria by HM1 was observed for a broad range of Gram-positive and Gram-negative bacteria. Therefore, the detailed view of peptide-lipid interactions described by the barnacle model consolidates it among the established models. Various antimicrobial peptides and proteins exert their antimicrobial activities by directly targeting the microbial membrane (1). Currently, only a few mechanistic models describe the peptides' modes of action in detail. Certain peptides form transient or stable membrane pores, as represented by the aggregate model, the toroidal-pore model, or the barrel stave model (2), or lead to micellization of membrane lipids, as specified by the carpet model (3). Furthermore, the peptides can translocate via the microbial membrane (aggregate model) and disturb essential intracellular processes. In addition, some antimicrobial peptides are reported to exert their modes of action more specifically, for example, by binding particular membrane compounds, such as lipid II, leading to inhibition of cell wall synthesis (4).Recently, members of a new antimicrobial protein family, the macins, were pronounced to exhibit a mode of action that clearly deviates from well-established mechanisms of membrane permeabilization. Peptides from this family lead to aggregation of bacteria, which originates from their striking molecular surface properties comprising two uncharged and hydrophobic hemispheres that sandwich a belt of positive charges (5, 6). The corresponding mechanistic model was termed the barnacle model and was described for the first time for hydramacin-1 (HM1), the macin family founder (5). It suggested a dual electrostatic, as well as hydrophobic, peptide-membrane interaction applied in parallel to two individual bact...

Honey Glycoproteins Containing Antimicrobial Peptides, Jelleins of the Major Royal Jelly Protein 1, Are Responsible for the Cell Wall Lytic and Bactericidal Activities of Honey

“…The main events involved in bacterial killing by AMPs include attachment to the bacterial membrane, insertion and membrane permeabilization via formation of transmembrane pores and micellarization or dissolution of the membrane [ 30 , 31 ]. Several models have been proposed to provide a mechanistic view of how the transmembrane pores are formed and lead to the membrane lysis: the barrel-stave model [ 32 ], the lytic, detergent-like mechanism represented by the “carpet” model [ 33 ] and most recently, the barnacle model [ 34 ]. Interestingly, recently discovered AMP hydramacin-1 isolated from Hydra , also displayed action with double functionality including bacterial agglutination and membrane disruptions in both Gram-negative and Gram positive bacteria [ 34 ].…”

Structure and Interactions of A Host Defense Antimicrobial Peptide Thanatin in Lipopolysaccharide Micelles Reveal Mechanism of Bacterial Cell Agglutination

“…In contrast to pore forming AMPs, cell agglutinating AMPs do not permeabilize cell membrane. Rather, as a mode of action, they directly interact with the outer membrane lipopolysaccharide (LPS) of Gram negative or cell wall peptidoglycans of Gram positive bacteria 10 – 13 . Atomic-resolution structures of cell agglutinating AMPs in complex with LPS or peptidoglycans would be essential to garner mechanistic insights in cell killing.…”

Piloting the Membranolytic Activities of Peptides with a Self‐organizing Map

“…[42,43] Briefly, this descriptor method results in a sequence-length-independent numerical molecular representation of the pharmacophoric feature distribution (hydrogen bonding, lipophilic, aromatic, charged interaction potential) along the amino acid sequence. [44] It captures all pairwise residue correlation patterns along the peptide sequence.…”

“…[17] We chose this molecular representation because it exhaustively captures residue neighborhoods, which was shown to be important for the activities of some AMPs with direct membrane lytic activity. [42, 43] Briefly, this descriptor method results in a sequence-length-independent numerical molecular representation of the pharmacophoric feature distribution (hydrogen bonding, lipophilic, aromatic, charged interaction potential) along the amino acid sequence. [44] It captures all pairwise residue correlation patterns along the peptide sequence.…”