A Cholesterol Biosynthesis Inhibitor Blocks Staphylococcus aureus Virulence

Abstract

Staphylococcus aureus produces hospital-and community-acquired infections, with methicillinresistant S. aureus posing a serious public health threat. The golden carotenoid pigment of S. aureus, staphyloxanthin, promotes resistance to reactive oxygen species and host neutrophil-based killing, and early enzymatic steps in staphyloxanthin production resemble those for cholesterol biosynthesis. We determined the crystal structures of S. aureus dehydrosqualene synthase (CrtM) at 1.58 angstrom resolution, finding structural similarity to human squalene synthase (SQS). We screened nine SQS inhibitors and determined the structures of three, bound to CrtM. One, previously tested for cholesterol-lowering activity in humans, blocked staphyloxanthin biosynthesis in vitro (median inhibitory concentration ~100 nM), resulting in colorless bacteria with increased susceptibility to killing by human blood and to innate immune clearance in a mouse infection model. This finding represents proof of principle for a virulence factor-based therapy against S. aureus.Over the past 20 years, there has been an explosion in the prevalence of antibiotic-resistant bacterial infections, both in the hospital and in the general community; in the United States,

Inhibition of staphyloxanthin biosynthesis in Staphylococcus aureus by rhodomyrtone, a novel antibiotic candidate

“…In contrast, the compound probably induced the activity of the CrtM enzyme, which condenses two molecules of farnesyl diphosphate to form dehydrosqualene. A team of researchers discovered recently that inhibition of S. aureus CrtM and CrtN reduced bacterial survival during infections, suggesting a novel virulencetargeted approach for antibiotic therapy (Hammond & White, 1970a, b;Liu et al, 2008). The first committed step in the staphyloxanthin biosynthetic pathway proceeds through presqualene diphosphate and then dehydrosqualene, catalysed by CrtM (Pelz et al, 2005), and is very similar to that catalysed by SQS in plants, animals and some protozoa, as demonstrated in Fig.…”

“…Liu et al (2005) reported that blocking S. aureus carotenogenesis made the organism more susceptible to killing by 1.5 % H 2 O 2 and decreased whole-blood survival. Moreover, non-pigmented S. aureus cells were more susceptible to innate immune clearance in a mouse infection model (Liu et al, 2008).…”

“…1 (Song et al, 2009b). Liu et al (2008) recently observed that the crystal structure of S. aureus CrtM is very similar to that of human SQS used in cholesterol biosynthesis in humans (Liu et al, 2008). However, a distinction occurs in the last step of catalysis.…”

“…Staphyloxanthin of S. aureus is a virulence factor for the organism (Song et al, 2009a, b). The golden-coloured pigment is a typical secondary metabolite that is not essential for growth and reproduction of the pathogen (Liu et al, 2008) but might aid invasiveness in vivo (Pelz et al, 2005). To investigate the biological activities of rhodomyrtone on S. aureus pigment production, carotenoids were extracted from rhodomyrtone-treated S. aureus.…”

“…Inhibition of the CrtN enzyme by diphenylamine has been known for many years to result in colourless bacteria (Hammond & White, 1970a, b). Liu et al (2008) Fig. 1.…”