Effects of microplusin, a copper-chelating antimicrobial peptide, against Cryptococcus neoformans

Abstract

Microplusin is an antimicrobial peptide isolated from the cattle tick Rhipicephalus (Boophilus) microplus. Its copper-chelating ability is putatively responsible for its bacteriostatic activity against Micrococcus luteus as microplusin inhibits respiration in this species, which is a copper-dependent process. Microplusin is also active against Cryptococcus neoformans (MIC(50) = 0.09 μM), the etiologic agent of cryptococcosis. Here, we show that microplusin is fungistatic to C. neoformans and this inhibitory effect is abrogated by copper supplementation. Notably, microplusin drastically altered the respiratory profile of C. neoformans. In addition, microplusin affects important virulence factors of this fungus. We observed that microplusin completely inhibited fungal melanization, and this effect correlates with the inhibition of the related enzyme laccase. Also, microplusin significantly inhibited the capsule size of C. neoformans. Our studies reveal, for the first time, a copper-chelating antimicrobial peptide that inhibits respiration and growth of C. neoformans and modifies two major virulence factors: melanization and formation of a polysaccharide capsule. These features suggest that microplusin, or other copper-chelation approaches, may be a promising therapeutic for cryptococcosis.

Mechanisms of Infection by the Human Fungal Pathogen Cryptococcus Neoformans

“…High expression of the copper transporter protein Ctr4 was observed in both macrophage-internalized and brain isolated cryptococci, implying that copper acquisition is essential for C. neoformans intracellular survival and dissemination to the brain [93]. Denying C. neoformans access to copper by the copper chelator microplusin reduces growth and completely inhibits melanization in vitro [94]. In addition to copper, iron is an essential micronutrient required by many microbial organisms.…”

Regulation of Copper Toxicity by Candida albicans GPA2

“…Alspaugh et al demonstrated that CnGPA1 regulates capsule production and melanization by showing that a strain harboring a deletion in CnGPA1 displays defects in these processes (37). In a study performed 14 years later, Silva et al observed that treatment of C. neoformans cells with microplusin, a copper-chelating antimicrobial peptide, inhibited both capsule production and melanization (42). One possible explanation for the similarities in phenotypes shared by deletion of CnGPA1 and depletion of copper by chelation is that a Cngpa1⌬ mutant has a defect in copper import, similar to what we observed in C. albicans.…”

Functional analysis of a novel cysteine-rich antimicrobial peptide from the salivary glands of the tick Rhipicephalus haemaphysaloides

“…A large number of AMPs have been identified in different organisms; these AMPs can be effective and powerful weapons in plants and invertebrate animals with respect to resisting infection by pathogenic microbes (Li et al 2007). Several small AMPs, such as Hb98-114, defDM, microplusin, vitellin-degrading cysteine endopeptidase (VTDCE), and HlMS-defensin, have been identified from the hemolymph, salivary glands, and midgut of ticks Silva et al 2011;Belmonte et al 2012;Oldiges et al 2012;Zheng et al 2012;Chrudimská et al 2014). These naturally occurring molecules exhibit peptidase activity, play a defensive role in ticks, and are highly potent against several bacterial, fungi, yeast, and Lyme borreliosis spirochetes (Bulet et al 1999;Hynes et al 2005;Esteves et al 2009).…”