Protegrin-4

The porcine leukocyte protegrins are a family of cysteine-rich antimicrobial peptides the primary structures of which combine features of defensins and tachyplesins. We cloned three protegrins from porcine bone marrow mRNA by PCR, including one (PG-4) that was previously unknown. The 691 bp protegrin cDNAs were > 98.8% identical, and each was surrounded by highly conserved 5' and (in some instances) 3' sequences present in structurally dissimilar antimicrobial and LPS-binding peptides of animal leukocytes.

Protegrin-4 (PG-4) is a member of the porcine leukocyte protegrins family of cysteine-rich antimicrobial peptides (AMPs) isolated from Sus scrofa. It consists of 18 amino acid residues and works as a part of innate immune system. In this study, we examined the intrinsic aggregation propensity of this AMP using multiple computational algorithms, namely, TANGO, AGGRESCAN, FOLDAMYLOID, AMYLPRED, and ZYGGREGATOR, and found that the peptide is predicted to have a high propensity for the β sheet formation that disposes this peptide to be amyloidogenic. Under in vitro conditions, PG-4 formed visible aggregates and displayed the hallmark properties of typical amyloids such as enhanced binding of Congo red, increased fluorescence with Thioflavin-T, and fibrillar morphology under transmission electron microscopy. Then we examined its antimicrobial activity against Bacillus subtilis and found that the aggregated peptide retained its antimicrobial activity. Additionally, the aggregates remain non-toxic to the HEK293 and Caco2 cells. Our study suggests that the inherent aggregation properties of AMP can rationally be explored as a potential source of peptide-based antimicrobials with enhanced stability.

Respiratory infections are a real threat for humans, and therefore the pig model is of interest for studies. As one of a case for studies, Actinobacillus pleuropneumoniae (APP) caused infections and still worries many pig breeders around the world. To better understand the influence of pathogenic effect of APP on a respiratory system-lungs and tracheobronchial lymph nodes (TBLN), we aimed to employ matrix-assisted laser desorption/ionization time-of-flight mass spectrometry imaging (MALDI-TOF MSI). In this study, six pigs were intranasally infected by APP and two were used as non-infected control, and 48 cryosections have been obtained. MALDI-TOF MSI and immunohistochemistry (IHC) were used to study spatial distribution of infectious markers, especially interleukins, in cryosections of porcine tissues of lungs (necrotic area, marginal zone) and tracheobronchial lymph nodes (TBLN) from pigs infected by APP. CD163, interleukin 1β (IL‑1β) and a protegrin-4 precursor were successfully detected based on their tryptic fragments. CD163 and IL‑1β were confirmed also by IHC. The protegrin-4 precursor was identified by MALDI-TOF/TOF directly on the tissue cryosections. CD163, IL‑1β and protegrin‑4 precursor were all significantly (p < 0.001) more expressed in necrotic areas of lungs infected by APP than in marginal zone, TBLN and in control lungs.