Activity of Protegrins against Yeast-Phase Candida albicans

Abstract

We used a two-stage radial diffusion assay to perform a structure-activity study of the antifungal effects of protegrin-1 (PG-1) on yeast-phase Candida albicans. While doing so, we computed MICs from the radial diffusion assay data by three methods and compared the respective values with results from colony count and broth microdilution assays. This allowed us to identify several technical modifications that improved the sensitivity and accuracy of radial diffusion assays. We found that both PG-1 and enantiomeric PG-1 (composed exclusively of d-amino acids) were potently fungicidal for yeast-phase C. albicans. The protegrins PG-2, -3, and -5, but not PG-4, were as effective as PG-1. At least one intramolecular disulfide bond was required to retain optimal candidacidal activity at physiological NaCl concentrations. Truncated variants of PG-1 that lacked its first four residues showed decreased candidacidal activity, although their activity against bacteria was substantially intact. Altering the β-turn region (residues 9 to 12) of PG-1 or its variants further decreased candidacidal activity. These studies suggest that only 12 residues are needed to endow protegrin molecules with strong antibacterial activity and that at least 4 additional residues are needed to add potent antifungal properties. Thus, the 16-residue protegrin PG-2 likely represents the minimal structure needed for broad-spectrum antimicrobial activity encompassing bacteria and fungi.

Antifungal activity of synthetic peptide derived from halocidin, antimicrobial peptide from the tunicate, Halocynthia aurantium

“…As a result, di‐K19Hc emerged as the most promising candidate for the development of a new antibiotic against antibiotic‐resistant bacteria. As in the case of many other peptides, including cecropin [29], magainin II [30], and protegrin [31], all of which exhibited antifungal and antibacterial effects, di‐K19Hc was also anticipated to exhibit antifungal properties. Hence, in this study, we have assessed the activity of di‐K19Hc against a panel of fungi, in a series of assays that were conducted in accordance with NCCLS procedures.…”

Clavaspirin, an antibacterial and haemolytic peptide from Styela clava

“…The diameters of the clear zones were measured to the nearest 0.1 mm, and were expressed in units after subtracting the well diameter, 3.2 mm (10 units = 1 mm). The principles of the radial diffusion assay (9,10) and when it may be preferable to National Committee for Clinical Laboratory Standards (NCCLS) microbroth dilution assays for studying cationic peptides (11).…”

Antimicrobial peptides: key components of the innate immune system

“…However, this rigid structure, in naturally occurring forms, prevents PG to undergo significant conformational changes upon association with membranes or upon oligomerization and also accounts for higher toxicity against eukaryotic cells (Ostberg and Kaznessis, 2005). In contrast to defensins, disulphide bond in PG is necessary for their antimicrobial activity, removing them decreases the activity significantly or abolishes it totally (Tamamura et al, 1995;Qu et al, 1997;Cho et al, 1998b). Recently Wang et al, showed that disulphide in Ib-AMP1, a 20-residue β-sheet AMP found in the seeds of Impatiens balsamina, is responsible for the intracellular activity.…”