Novel antimicrobial peptides from the venom of the eusocial bee Halictus sexcinctus (Hymenoptera: Halictidae) and their analogs

Abstract

Two novel antimicrobial peptides, named halictines, were isolated from the venom of the eusocial bee Halictus sexcinctus. Their primary sequences were established by ESI-QTOF mass spectrometry, Edman degradation and enzymatic digestion as Gly-Met-Trp-Ser-Lys-Ile-Leu-Gly-His-Leu-Ile-Arg-NH2 (HAL-1), and Gly-Lys-Trp-Met-Ser-Leu-Leu-Lys-His-Ile-Leu-Lys-NH2 (HAL-2). Both peptides exhibited potent antimicrobial activity against Gram-positive and Gram-negative bacteria but also noticeable hemolytic activity. The CD spectra of HAL-1 and HAL-2 measured in the presence of trifluoroethanol or SDS showed ability to form an amphipathic alpha-helical secondary structure in an anisotropic environment such as bacterial cell membrane. NMR spectra of HAL-1 and HAL-2 measured in trifluoroethanol/water confirmed formation of helical conformation in both peptides with a slightly higher helical propensity in HAL-1. Altogether, we prepared 51 of HAL-1 and HAL-2 analogs to study the effect of such structural parameters as cationicity, hydrophobicity, alpha-helicity, amphipathicity, and truncation on antimicrobial and hemolytic activities. The potentially most promising analogs in both series are those with increased net positive charge, in which the suitable amino acid residues were replaced by Lys. This improvement basically relates to the increase of antimicrobial activity against pathogenic Pseudomonas aeruginosa and to the mitigation of hemolytic activity.

The antifungal effect of peptides from hymenoptera venom and their analogs

“…The peptides were prepared by the solid-phase method as previously described [22][23][24]26]. They were purified by preparative RP-HPLC using a Vydac C-18 column (250 x 10 mm) at a 3.0 ml/min flow rate.…”

“…The antibacterial activity of the new analogs was determined quantitatively as previously described [22][23][24]26] …”

“…Hemolytic activity was tested using rat or human (healthy volunteer) red blood cells as described previously [22][23][24].…”

“…Very recently, we have identified new AMPs, one in the venom of the solitary cleptoparasitic bee Melecta albifrons which we named melectin, MEP [22], three in the venom of the eusocial bee Lasioglossum laticeps which we have named lasioglossins, LL-I, LL-II and LL-III [23], and two from the eusocial bee Halictus sexcinctus which we named halictines, HAL-1 and HAL-2 [24]. For their structures and molecular weights see Table 1.…”

“…In this paper, we focused our attention on antifungal activity using as an experimental model the yeast Candida. We studied the antifungal effect not only of the AMPs and their analogs already described [22][23][24] but also of some new structural analogs, whose synthesis will be described elsewhere, against the five most common Candida species. A preliminary communication has been published [25].…”