Cryptococcus neoformans laccase catalyses melanin synthesis from both d- and l-DOPA

Abstract

The human fungal pathogen Cryptococcus neoformans produces melanin in the presence of various substrates, including the L enantiomer of 3,4-dihydroxyphenylalanine (DOPA). The enzyme laccase catalyses the formation of melanin by oxidizing L-DOPA, initiating a series of presumably spontaneous reactions that ultimately leads to the polymerization of the pigment in the yeast cell wall. There, melanin protects the cell from a multitude of environmental and host assaults. Thus, the ability of C. neoformans to produce pigments from a variety of available substrates is likely to confer a survival advantage. A number of C. neoformans isolates of different serotypes produced pigments from D-DOPA, the stereoisomer of L-DOPA. Acid-resistant particles were isolated from pigmented C. neoformans cells grown in the presence of D-DOPA. Biophysical characterization showed the particles had a stably detectable free-radical signal by EPR, and negative zeta potential, similar to L-DOPA-derived particles. No major differences were found between L-and D-DOPA ghosts in terms of binding to anti-melanin antibodies, or in overall architecture when imaged by electron microscopy. C. neoformans cells utilized L-and D-DOPA at a similar rate. Overall, our results indicate that C. neoformans shows little stereoselectivity for utilizing DOPA in melanin synthesis. The ability of C. neoformans to use both L and D enantiomers for melanization implies that this organism has access to a greater potential pool of substrates for melanin synthesis, and this could potentially be exploited in the design of therapeutic inhibitors of laccase.

Growth and Pigment Production on d -Tryptophan Medium by Cryptococcus gattii , Cryptococcus neoformans , and Candida albicans

“…D-DOPA can also serve as a substrate, and melanization occurred equally well with both enantiomers (15). Both laccase and the pigment melanin are associated with the virulence of C. neoformans (39,40,47,58).…”

Polyphenoloxidase Silencing Affects Latex Coagulation in Taraxacum Species

“…In the presence of 3,4-dihydroxy-L-phenylalanine (L-DOPA), a PPO substrate that is also oxidized by laccases (Eisenman et al, 2007) and peroxidases (Albrecht and Kohlenbach, 1990), we observed total latex enzymatic activities of approximately 0.218 mkat mg 21 (T. officinale) and approximately 0.237 mkat mg 21 (T. kok-saghyz). Addition of the potent PPO inhibitor tropolone (Fuerst et al, 2006) caused a significant reduction in the total enzymatic activity to approximately 0.004 mkat mg 21 for T. officinale and approximately 0.002 mkat mg 21 for T. koksaghyz (Fig.…”

Melanins: Skin Pigments and Much More—Types, Structural Models, Biological Functions, and Formation Routes

“…This basidiomycetous fungus infects the human brain and it contains a very active phenol oxidase able to oxidize the catecholamine neurotransmitters, dopamine, and norepinephrine to melanin polymers [120,121]. As these pigments are formed in the brain after infection, a pathogenic neuromelanin is formed using brain compounds [122] and that increases the virulence of the infection. On the other hand, C. neoformans is also able to synthesize pyomelanin derived from a fungal metabolite, homogentisic acid (HGA, Figure 1(h)) [123].…”