Pathway of sulfate assimilation in bacteria - Sulfate uptake and assimilation - HORT640 - Metabolic Plant Physiology - Department of Horticulture and Landscape Architecture

In fungi, the pathway of sulfate assimilation proceeds via a similar reaction sequence as shown for bacteria, above [for a recent review of the molecular genetics of sulfur assimilation in yeast and filamentous fungi, see Marzluf (1997)]. In Aspergillus nidulans ATP sulfurylase (sulphurylase) and APS kinase are encoded by genes sCand sD, respectively (Clarke et al, 1997). Fungal ATP sulfurylase is allosterically inhibited by 3'-phosphoadenosine 5'-phosphosulfate (PAPS), the product of adenosine 5'-phosphosulfate (APS) kinase, the second enzyme in the sulfate activation sequence (MacRae and Segel, 1997).

In the yeast, Saccharomyces cerevisiae, mutations in six different loci (MET1, MET4, MET8, MET16, MET22, and MET25) have been reported to result in the absence of PAPS reductase activity (Thomas et al, 1990). MET16 is the structural gene for PAPS reductase; the yeast and the Escherichia coli enzymes display significant similarities (Thomas et al, 1990). Thioredoxin has been implicated in the reduction of PAPS in Saccharomyces cerevisiae as well as in E. coli; thioredoxin is proposed to play a role as a thiol carrier in the reduction of PAPS into sulfite (Thomas et al, 1990).

The MET17 and MET25 genes of Saccharomyces cerevisiae encode the enzyme O-acetylhomoserine, O-acetylserine sulfhydrylase (OAH-OAS sulphydrylase) (D'Andrea et al, 1987). met17 and met25 are both mutations in the structural gene for the OAH-OAS sulfhydrylase subunit and that each affects a different functional domain of the enzyme allowing subunit complementation in the met17 X met25 diploid (D'Andrea et al, 1987). met17 and met25 mutants are devoid of PAPS reductase activity; this activity is fully restored in the met17 X met25 diploid. This suggests interactions between OAH-OAS sulfhydrylase and PAPS reductase (D'Andrea et al, 1987). In Saccharomyces cerevisiae, the MET25 gene is repressed by the presence of S-adenosylmethionine (AdoMet) in the growth medium (Thomas et al, 1989).

In bacteria, fungi, yeast and plants, the two enzymes ATP sulfurylase and APS kinase are present on separate polypeptide chains. However, in the marine worm, Urechis caupo, Drosophila, mouse and humans, ATP sulfurylase and APS kinase activities occur as a bifunctional enzyme, PAPS synthetase (Rosenthal and Leustek, 1995; Li et al, 1995, Jullien et al, 1997) [the human homolog is termed PAPS synthase (Venkatachalam et al, 1998; Yanagisawa et al, 1998)]. The NH₂-terminal portion of the protein contains APS kinase activity and the COOH-terminal portion ATP sulfurylase (Venkatachalam et al, 1999). The animal genes may have evolved through the fusion of the ATP sulfurylase- and APS kinase-encoding genes from lower organisms (Rosenthal and Leustek, 1995). Fusion of the two enzymes specifically enhances the intrinsic stability of the sulfurylase activity (Deyrup et al, 1999). Sequence alignment analysis of PAPS synthases and the superfamily of TagD-related nucleotidylyltransferases reveals the presence of a highly conserved HXGH motif in the ATP sulfurylase domain of PAPS synthases, a motif implicated in the alpha-beta phosphodiesterase activity of cytidylyltransferases (Venkatachalam et al, 1999).

The cysK gene of Escherichia coli encodes O-acetylserine sulfydrylase A (Levy and Danchin, 1988). The deduced amino acid sequence of the carboxy-terminal moiety of O-acetylserine sulfydrylase A [EC 4.2.99.8] shows significant similarity to the amino acid sequence of tryptophan synthase beta chain [EC 4.2.1.20] from several organisms (Levy and Danchin, 1988). This sequence similarity reflects the structural homologies of substrates shared by both enzymes. These proteins, although catalyzing different reactions in distinct metabolic pathways, may have evolved from a common ancestral gene (Levy and Danchin, 1988). This sequence similarity was confirmed and extended to other pyridoxal-phosphate-dependent enzymes by Bork and Rohde (1990). Tryptophan synthase beta subunit consensus motifs share significant similarities with O-acetylserine sulfhydrolases [EC 4.2.99.8], threonine synthases [EC 4.2.99.2], L- and D-serine dehydratases [EC 4.2.1.13/EC 4.2.1.14] and threonine dehydratases [EC 4.2.1.16] (Bork and Rohde, 1990).

References

Bork P, Rohde K 1990 Sequence similarities between tryptophan synthase beta subunit and other pyridoxal-phosphate-dependent enzymes. Biochem. Biophys. Res. Commun. 171: 1319-1325.

Clarke DL, Newbert RW, Turner G 1997 Cloning and characterisation of the adenosyl phosphosulphate kinase gene from Aspergillus nidulans. Curr. Genet. 32: 408-412.

D'Andrea R, Surdin-Kerjan Y, Pure G, Cherest H 1987 Molecular genetics of met 17 and met 25 mutants of Saccharomyces cerevisiae: intragenic complementation between mutations of a single structural gene. Mol. Gen. Genet. 207: 165-170.

Deyrup AT, Krishnan S, Singh B, Schwartz NB 1999 Activity and stability of recombinant bifunctional rearranged and monofunctional domains of ATP-sulfurylase and adenosine 5'-phosphosulfate kinase. J. Biol. Chem. 274: 10751-10757.

Jullien D, Crozatier M, Kas E 1997 cDNA sequence and expression pattern of the Drosophila melanogaster PAPS synthetase gene: a new salivary gland marker. Mech. Dev. 68: 179-186.

Levy S, Danchin A 1988 Phylogeny of metabolic pathways: O-acetylserine sulphydrylase A is homologous to the tryptophan synthase beta subunit. Mol. Microbiol. 2: 777-783.

Li H, Deyrup A, Mensch JR Jr, Domowicz M, Konstantinidis AK, Schwartz NB 1995 The isolation and characterization of cDNA encoding the mouse bifunctional ATP sulfurylase-adenosine 5'-phosphosulfate kinase. J. Biol. Chem. 270: 29453-29459.

MacRae I, Segel IH 1997 ATP sulfurylase from filamentous fungi: which sulfonucleotide is the true allosteric effector? Arch. Biochem. Biophys. 337: 17-26.

Marzluf GA 1997 Molecular genetics of sulfur assimilation in filamentous fungi and yeast. Annu. Rev. Microbiol. 51: 73-96.

Rosenthal E, Leustek T 1995 A multifunctional Urechis caupo protein, PAPS synthetase, has both ATP sulfurylase and APS kinase activities. Gene 165: 243-248.

Schmidt A, Jager K 1992 Open questions about sulfur metabolism in plants. Annu. Rev. Plant Physiol. 43: 325-349.

Thomas D, Barbey R, Surdin-Kerjan Y 1990 Gene-enzyme relationship in the sulfate assimilation pathway of Saccharomyces cerevisiae. Study of the 3'-phosphoadenylylsulfate reductase structural gene. J. Biol. Chem. 265: 15518-15524.

Thomas D, Cherest H, Surdin-Kerjan Y 1989 Elements involved in S-adenosylmethionine-mediated regulation of the Saccharomyces cerevisiae MET25 gene. Mol. Cell Biol. 9: 3292-3298.

Venkatachalam KV, Akita H, Strott CA 1998 Molecular cloning, expression, and characterization of human bifunctional 3'-phosphoadenosine 5'-phosphosulfate synthase and its functional domains. J. Biol. Chem. 273: 19311-19320.

Venkatachalam KV, Fuda H, Koonin EV, Strott CA 1999 Site-selected mutagenesis of a conserved nucleotide binding HXGH motif located in the ATP sulfurylase domain of human bifunctional 3'-phosphoadenosine 5'-phosphosulfate synthase. J. Biol. Chem. 274: 2601-2604.

Yanagisawa K, Sakakibara Y, Suiko M, Takami Y, Nakayama T, Nakajima H, Takayanagi K, Natori Y, Liu MC 1998 cDNA cloning, expression, and characterization of the human bifunctional ATP sulfurylase/adenosine 5'-phosphosulfate kinase enzyme. Biosci. Biotechnol. Biochem. 62: 1037-1040.


David Rhodes Department of Horticulture & Landscape Architecture Horticulture Building 625 Agriculture Mall Drive Purdue University West Lafayette, IN 47907-2010 Last Update: 10/01/09