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PDBsum entry 4wcx
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References listed in PDB file
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Key reference
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Title
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X-Ray crystallographic and epr spectroscopic analysis of hydg, A maturase in [fefe]-Hydrogenase h-Cluster assembly.
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Authors
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P.Dinis,
D.L.Suess,
S.J.Fox,
J.E.Harmer,
R.C.Driesener,
L.De la paz,
J.R.Swartz,
J.W.Essex,
R.D.Britt,
P.L.Roach.
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Ref.
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Proc Natl Acad Sci U S A, 2015,
112,
1362-1367.
[DOI no: ]
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PubMed id
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Abstract
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Hydrogenases use complex metal cofactors to catalyze the reversible formation of
hydrogen. In [FeFe]-hydrogenases, the H-cluster cofactor includes a diiron
subcluster containing azadithiolate, three CO, and two CN(-) ligands. During the
assembly of the H cluster, the radical S-adenosyl methionine (SAM) enzyme HydG
lyses the substrate tyrosine to yield the diatomic ligands. These diatomic
products form an enzyme-bound Fe(CO)x(CN)y synthon that serves as a precursor
for eventual H-cluster assembly. To further elucidate the mechanism of this
complex reaction, we report the crystal structure and EPR analysis of HydG. At
one end of the HydG (βα)8 triosephosphate isomerase (TIM) barrel, a canonical
[4Fe-4S] cluster binds SAM in close proximity to the proposed tyrosine binding
site. At the opposite end of the active-site cavity, the structure reveals the
auxiliary Fe-S cluster in two states: one monomer contains a [4Fe-5S] cluster,
and the other monomer contains a [5Fe-5S] cluster consisting of a [4Fe-4S]
cubane bridged by a μ2-sulfide ion to a mononuclear Fe(2+) center. This fifth
iron is held in place by a single highly conserved protein-derived ligand:
histidine 265. EPR analysis confirms the presence of the [5Fe-5S] cluster, which
on incubation with cyanide, undergoes loss of the labile iron to yield a
[4Fe-4S] cluster. We hypothesize that the labile iron of the [5Fe-5S] cluster is
the site of Fe(CO)x(CN)y synthon formation and that the limited bonding between
this iron and HydG may facilitate transfer of the intact synthon to its cognate
acceptor for subsequent H-cluster assembly.
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