The Role of Amino Acid Permeases and Tryptophan Biosynthesis in <i>Cryptococcus neoformans</i> Survival

<div><p>Metabolic diversity is an important factor during microbial adaptation to different environments. Among metabolic processes, amino acid biosynthesis has been demonstrated to be relevant for survival for many microbial pathogens, whereas the association between pathogenesis and amino acid uptake and recycling are less well-established. <i>Cryptococcus neoformans</i> is an opportunistic fungal pathogen with many habitats. As a result, it faces frequent metabolic shifts and challenges during its life cycle. Here we studied the <i>C</i>. <i>neoformans</i> tryptophan biosynthetic pathway and found that the pathway is essential. RNAi indicated that interruptions in the biosynthetic pathway render strains inviable. However, auxotroph complementation can be partially achieved by tryptophan uptake when a non preferred nitrogen source and lower growth temperature are applied, suggesting that amino acid permeases may be the target of nitrogen catabolism repression (NCR). We used bioinformatics to search for amino acid permeases in the <i>C</i>. <i>neoformans</i> and found eight potential global permeases (<i>AAP</i>1 to <i>AAP</i>8). The transcriptional profile of them revealed that they are subjected to regulatory mechanisms which are known to respond to nutritional status in other fungi, such as (i) quality of nitrogen (<u>N</u>itrogen <u>C</u>atabolism <u>R</u>epression, NCR) and carbon sources (<u>C</u>arbon <u>C</u>atabolism <u>R</u>epression, CCR), (ii) amino acid availability in the extracellular environment (SPS-sensing) and (iii) nutritional deprivation (<u>G</u>lobal <u>A</u>mino <u>A</u>cid <u>C</u>ontrol, GAAC). This study shows that <i>C</i>. <i>neoformans</i> has fewer amino acid permeases than other model yeasts, and that these proteins may be subjected to complex regulatory mechanisms. Our data suggest that the <i>C</i>. <i>neoformans</i> tryptophan biosynthetic pathway is an excellent pharmacological target. Furthermore, inhibitors of this pathway cause <i>Cryptococcus</i> growth arrest <i>in vitro</i>.</p>