Genetics and Physiology of Sulfur Metabolism in Aspergillus
Andrzej Paszewski, Jerzy Brzywczy, Marzena Sieńko and Sebastian Piłsyk
from: Aspergillus and Penicillium in the Post-genomic Era (Edited by: Ronald P. de Vries, Isabelle Benoit Gelber and Mikael Rørdam Andersen). Caister Academic Press, U.K. (2016) Pages: 113-128.
Aspergillus nidulans, as many other fungi, can utilize sulfate as a sulfur source through a highly energy consuming sulfate assimilation pathway producing sulfide which is then incorporated into cysteine. When cysteine is in excess this pathway is repressed by the hierarchical sulfur metabolite repression (SMR) system, in which the SCF ubiquitin ligase activated by cysteine brings about degradation of the MetR transcription factor specific for sulfate assimilation pathway genes. Mutational impairment of SMR causes a permanent derepression of the sulfate assimilation pathway and leads to a direct synthesis of homocysteine from sulfide as an alternative route of synthesis of sulfur amino acids. This derepression results in overproduction of sulfide and sulfur-containing organic compounds associated with a considerable dissipation of ATP and NADPH. Transcriptomic analysis of mutants dysregulated in SMR has revealed considerable remodeling of cellular metabolism manifested by changes in the levels of several hundred transcripts. Among the up‑regulated genes the most remarkable are those encoding proteins normally involved in responses to various environmental stresses. Expression of genes encoding enzymes involved in homocysteine metabolism is independent of SMR and is activated by this amino acid, which prevents its accumulation above a toxic level read more ...