title: A conserved mechanism for sulfonucleotide reduction.
abstract: Sulfonucleotide reductases are a diverse family of enzymes that catalyze the first committed step of reductive sulfur assimilation. In this reaction, activated sulfate in the context of adenosine-5'-phosphosulfate (APS) or 3'-phosphoadenosine 5'-phosphosulfate (PAPS) is converted to sulfite with reducing equivalents from thioredoxin. The sulfite generated in this reaction is utilized in bacteria and plants for the eventual production of essential biomolecules such as cysteine and coenzyme A. Humans do not possess a homologous metabolic pathway, and thus, these enzymes represent attractive targets for therapeutic intervention. Here we studied the mechanism of sulfonucleotide reduction by APS reductase from the human pathogen Mycobacterium tuberculosis, using a combination of mass spectrometry and biochemical approaches. The results support the hypothesis of a two-step mechanism in which the sulfonucleotide first undergoes rapid nucleophilic attack to form an enzyme-thiosulfonate (E-Cys-S-SO(3-)) intermediate. Sulfite is then released in a thioredoxin-dependent manner. Other sulfonucleotide reductases from structurally divergent subclasses appear to use the same mechanism, suggesting that this family of enzymes has evolved from a common ancestor.
authors: Department of Chemistry, University of California, Berkeley, California, USA.
authors: Kate S
authors: KS
authors: Carroll
authors: Hong
authors: H
authors: Gao
authors: Huiyi
authors: H
authors: Chen
authors: C David
authors: CD
authors: Stout
authors: Julie A
authors: JA
authors: Leary
authors: Carolyn R
authors: CR
authors: Bertozzi
mesh_terms: D000250:Adenosine Phosphosulfate / Q000737:chemistry*; D002384:Catalysis; D003545:Cysteine / Q000737:chemistry; D004926:Escherichia coli / Q000201:enzymology; D005583:Fourier Analysis; D013058:Mass Spectrometry / Q000379:methods; D008969:Molecular Sequence Data; D009169:Mycobacterium tuberculosis / Q000201:enzymology*; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000737:chemistry* / Q000378:metabolism; D010724:Phosphoadenosine Phosphosulfate / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000201:enzymology; D017386:Sequence Homology, Amino Acid; D013447:Sulfites / Q000378:metabolism; D013879:Thioredoxins / Q000378:metabolism
chemical_list: D013447:Sulfites; D010724:Phosphoadenosine Phosphosulfate; D000250:Adenosine Phosphosulfate; D013879:Thioredoxins; D010088:Oxidoreductases; D050862:Oxidoreductases Acting on Sulfur Group Donors; C052449:3'-phosphoadenylyl-5'-phosphosulfate reductase; C019618:adenylylsulfate reductase; D003545:Cysteine