1jhd
Crystal Structure of Bacterial ATP Sulfurylase from the Riftia pachyptila Symbiont
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OverviewOverview
In sulfur chemolithotrophic bacteria, the enzyme ATP sulfurylase functions, to produce ATP and inorganic sulfate from APS and inorganic pyrophosphate, which is the final step in the biological oxidation of hydrogen sulfide to, sulfate. The giant tubeworm, Riftia pachyptila, which lives near, hydrothermal vents on the ocean floor, harbors a sulfur chemolithotroph as, an endosymbiont in its trophosome tissue. This yet-to-be-named bacterium, was found to contain high levels of ATP sulfurylase that may provide a, substantial fraction of the organisms ATP. We present here, the crystal, structure of ATP sulfurylase from this bacterium at 1.7 A resolution. As, predicted from sequence homology, the enzyme folds into distinct, N-terminal and catalytic domains, but lacks the APS kinase-like C-terminal, domain that is present in fungal ATP sulfurylase. The enzyme crystallizes, as a dimer with one subunit in the crystallographic asymmetric unit. Many, buried solvent molecules mediate subunit contacts at the interface., Despite the high concentration of sulfate needed for crystallization, no, ordered sulfate was observed in the sulfate-binding pocket. The structure, reveals a mobile loop positioned over the active site. This loop is in a, "closed" or "down" position in the reported crystal structures of fungal, ATP sulfurylases, which contained bound substrates, but it is in an "open", or "up" position in the ligand-free Riftia symbiont enzyme. Thus, closure, of the loop correlates with occupancy of the active site, although the, loop itself does not interact directly with bound ligands. Rather, it, appears to assist in the orientation of residues that do interact with, active-site ligands. Amino acid differences between the mobile loops of, the enzymes from sulfate assimilators and sulfur chemolithotrophs may, account for the significant kinetic differences between the two classes of, ATP sulfurylase.
About this StructureAbout this Structure
1JHD is a Single protein structure of sequence from Bacteria with SO4 and BR as ligands. Active as Sulfate adenylyltransferase, with EC number 2.7.7.4 Full crystallographic information is available from OCA.
ReferenceReference
Crystal structure of ATP sulfurylase from the bacterial symbiont of the hydrothermal vent tubeworm Riftia pachyptila., Beynon JD, MacRae IJ, Huston SL, Nelson DC, Segel IH, Fisher AJ, Biochemistry. 2001 Dec 4;40(48):14509-17. PMID:11724564
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