Sulfurylase: Application & Overview

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Sulfurylase: Overview

Sulfurylase is an enzyme that catalyzes the chemical reaction forming pyrophosphate and adenylyl sulfate as products from ATP and sulfate substrates. The enzyme is also known as Sulfate Adenylyltransferase, ATP sulfurylase (ATPS), or adenosine triphosphate sulfurylase. 

ATP + Sulfate ⇌ Pyrophosphate + Adenlyl sulfate

Sulfurylase belongs to the family of enzyme transferases that catalyze the transfer of a particular group from one chemical compound to the other. Sulfurylase specifically belongs to the nucleotidyl transferases that facilitate the transfer of phosphate-containing nucleotide groups.

The enzyme can be a monomer, homodimer, or homo-oligomer based on the type of organism. For example, in yeast and bacteria, the sulfurylase enzyme is observed in a homohexamer form. 

In Saccharomyces cerevisiae and Penicillium chrysogenum, the enzyme is comprised of four domains:

  • Domain I: It’s similar to pyruvate kinase, having an N-terminus end with beta-barrels.
  • Domain II: It’s composed of right-handed alpha beta folds. It has an active site and substrate-binding motif. The active site resides in the center of the enzyme, which is composed of hydrophobic residues towards the inside of the groove and hydrophilic residues towards the edge.
  • Domain III: It has a region that links domain I with domain II.
  • Domain IV: It forms a typical alpha/beta fold and contains the C-terminus of the sulfurylase enzyme.
Figure: The crystal structure of ATP sulfurylase.

These enzymes participate in three metabolic pathways: sulfur metabolism, purine metabolism, and seleno amino acid metabolism. 

Additionally, some sulfurylases are also associated with the APS kinase enzyme (or adenosyl phosphosulfate kinase) for PAPS (phosphoadenosine-phosphosulfate) synthesis from inorganic sulfate. This bifunctional APS kinase/ATP sulfurylase coupled enzyme is known as PAPS synthase (or 3′-phosphoadenosine 5′-phosphosulfate synthase). Some studies also refer to these coupled enzymes as PAPS synthetase.

In this article, we will cover the working mechanism of ATP sulfurylases, their functions in organisms, and their applications in a myriad of lab workflows and biotech industries.

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How Does Sulfurylase Work?

 The reaction involving sulfurylase is a two-step process:

  • First step: It involves the nonreductive adenylation of sulfate by ATP sulfurylase. The enzyme catalyzes the synthesis of adenosine 5′-phosphosulfate (APS) 5 and inorganic pyrophosphate (PPi) from sulfate and ATP substrates.

APS formation in the process is energetically unfavorable, which hinders the reaction to move forward. Thus, it needs to be eliminated. This is done by the enzyme APS reductase, which catalyzes the reduction of APS to bisulfite and AMP. The resulting sulfite supports the cysteine biosynthesis and completes the sulfur assimilation pathway.

Moreover, the PPi formed in the reaction also needs to be pulled out because it’s not thermodynamically favorable. Done by the enzyme pyrophosphatase.

  • Second step: At this step, the formation of PAPS occurs from the phosphorylation of the substrates adenosine 5′-phosphosulfate using ATP.

The sulfurylase enzyme also performs the assimilatory sulfur reduction and dissimilatory redox reactions. The reaction involved in the dissimilatory sulfate reduction include:

  • The Serine acetyltransferase (SAT) enzyme catalyzes the reduction of sulfate(+6) to Adenosine 5′-phosphosulfate (APS) without utilizing ATP.
  • Then, APS is further reduced to sulfite(+4) and then sulfide (-2). In the dissimilatory sulfate oxidation process, the sulfate adenylyltransferase enzyme combines the pyrophosphate (PPi) with APS to form sulfate.

Sulfurylase in plants

Sulfurylase is found in a range of organisms with different structural forms. For example, in E.coli it can be tetramer encoded by genes cysD and cysN genes. However, in Saccharomyces cerevisiae and Penicillium chrysogenum it’s found in hexamer forms.

Plants contain different isoforms of sulfurylase that are mainly located in the plastid and cytosol of plant cells. For example, the soybean has four sulfurylase isoforms, which include: GmATP sulfurylase I of ∼100 kDa (made of two catalytic subunits of 48-kDa), GmATP sulfurylase II, GmATP sulfurylase III, and GmATP sulfurylase IV.

In plants, PAPS has a role in tryptophan-derived (indolic) secondary metabolites such as glucosinolates (GSs) and the production of other S-containing methionine-derived (aliphatic). Additionally, it’s also involved in the plant sulfur assimilation pathway, which results in the improved environmental stress response in plants and nutrient content.

The uptake of sulfate through the sulfur assimilation pathway also provides a substrate for the synthesis of a wide range of metabolites, such as methionine, iron-sulfur clusters, cysteine, glutathione, thiamin, biotin, and glucosinolates.

Figure: A schematic diagram of the ATP sulfurylase role in the sulfate assimilation pathway of plants and its regulation by other factors.

What is Sulfurylase Used For?

Sulfurylase has a range of applications in organisms. That’s why it’s also an essential tool for performing a spectrum of lab assays. Some of which are mentioned below.

Sulfurylase Roles in Organisms

  • The enzyme has an essential role in assimilatory sulfur reduction and dissimilatory sulfur oxidation and reduction (or redox reaction).
  • It also participates in the biogeochemically relevant sulfur cycle.
  • In organisms, the sulfurylase enzyme has an essential role in the sulfate assimilation pathway of the organisms.
  • In Penicillium, the sulfurylase enzyme plays a key role in the allosteric regulation of sulfate assimilation.
  • In a variety of organisms, the enzyme facilitates the oxidation of sulfur compounds to sulfate.

Sulfurylase Uses in Labs

  • Sulfurylase is used in molecular biology and biochemistry labs for lab assays such as pyrosequencing, cDNA formation, genomic sequencing, and cloning.
  • Sulfurylase enzyme is used to develop transgenic soybean with enhanced cysteine and methionine concentration in soy seeds through sulfur assimilatory and cysteine/methionine biosynthesis pathways.
  • It also has an application in the experiments on Arabidopsis thaliana for the functional characterization of a gene encoding a fourth ATP sulfurylase isoform.
  • Plant labs use the enzyme to study ATP sulfurylase activity during plants’ salinity stress.

Sulfate Activation

ATP sulfurylase plays a central role in sulfate activation. In order to add sulfate to the alpha phosphate, the enzyme hydrolyzes the bond between the alpha and beta phosphates of ATP. This results in the formation of APS and PPi. However, the energy stored in the phosphoric-sulfuric acid anhydride bond of APS enables the reaction to move further forward.

The concentration of APS and PPi is thermodynamically unfavorable and maintained at low levels by the enzymes APS reductase and inorganic pyrophosphatase. The APS reductase is the first enzyme involved in the catalysis of sulfate reduction. On the other hand, the APS kinase with ATP leads to the formation of PAPS, a substrate for sulfotransferases that catalyze sulfations.

Figure: A schematic diagram of reactions catalyzed by ATP sulfurylase and further sulfate assimilation reaction.

What Industries Use Sulfurylase?

Due to their extensive roles in organisms, sulfurylase is one of the essential tools in research labs and industries to conduct research studies for understanding the plant stress response or sulfate regulation in other organisms.

Microbiology

In microbiology labs, the ATP sulfurylase enzyme is used to catalyze a sulfate assimilation reaction, genome sequencing of organisms, cDNA preparation, and understanding of the sulfite oxidation pathway in microbial species.

Biotechnology

The sulfurylase enzyme has a spectrum of functions in plant biotechnology labs, such as studying the regulation of sulfate assimilation and dissimilation pathways, the stress response in plants, and the development of transgenic plants with improved nutrient content.

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ATP sulfurylase is an enzyme that catalyzes the sulfation of ATP to form APS and inorganic pyrophosphate. The enzyme is ubiquitous and has many isoforms in different organisms. It has a key role in sulfur assimilation and dissimilation pathways.

In labs, recombinant sulfurylase or coupled ATP sulfurylase/APS kinase is used for experimental studies, like understanding the plant stress or enhancing the nutritive value of some plants, like soybean.

ATP sulfurylase has a myriad of applications in Life Sciences labs in experiments, such as sequencing, cloning, and genetic engineering.

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