High levels of Tryptophan reduce cell wall or membrane stress tolerance in Saccharomyces cerevisiae

Tryptophan (Trp) is a proteinogenic aromatic amino acid; however, high levels of Trp are toxic in animals and yeast with unknown mechanisms. Previously, we suggested that aromatic aminotransferase Aro9 is important for excess Trp degradation. Besides, Schroeder and Ikui showed that aro9Δis sensitive to membrane stress by sodium dodecyl sulfate. Therefore, Trp accumulation may reduce the cell wall or membrane (CW/M) stress tolerance through participation of cell wall integrity (CWI) pathway, which detects and responds to CW/M perturbations. In this study, we found that yeast mutants of the CWI mitogen-activated protein kinase cascade were susceptible to excess Trp. Also, the Trp degradation deficient mutant aro8Δaro9Δcells, in which Trp accumulation was confirmed, were sensitive to several CW/M stresses. These results indicated that accumulation of Trp is adverse for the CW/M stress resistance and may disturb appropriate signal transduction responding to the stress.