**Peicho Petkov 1, Elena Lilkova 2, Nevena Ilieva 2,3,\* and Leandar Litov <sup>1</sup>**


Received: 2 October 2019; Accepted: 28 October 2019; Published: 1 November 2019

**Abstract:** Antimicrobial peptides (AMPs) are a diverse group of membrane-active peptides which play a crucial role as mediators of the primary host defense against microbial invasion. Many AMPs are found to be fully or partially disordered in solution and to acquire secondary structure upon interaction with a lipid membrane. Here, we report molecular dynamics simulations studies on the solution behaviour of a specific AMP, bombinin H2. We show that in monomeric form in water solution the peptide is somewhat disordered and preferably adopts a helix-loop-helix conformation. However, when more than a single monomer is placed in the solution, the peptides self-associate in aggregates. Within the aggregate, the peptides provide each other with an amphipathic environment that mimics the water–membrane interface, which allows them to adopt a single-helix structure. We hypothesise that this is the mechanism by which bombinin H2 and, possibly, other small linear AMPs reach the target membrane in a functional folded state and are able to effectively exert their antimicrobial action on it.

**Keywords:** antimicrobial peptides; self-association; aggregation; promotion of folding
