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PDBsum entry 1jpj
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Signaling protein
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PDB id
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1jpj
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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The conformation of bound gmppnp suggests a mechanism for gating the active site of the srp gtpase.
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Authors
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S.Padmanabhan,
D.M.Freymann.
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Ref.
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Structure, 2001,
9,
859-867.
[DOI no: ]
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PubMed id
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Abstract
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BACKGROUND: The signal recognition particle (SRP) is a phylogenetically
conserved ribonucleoprotein that mediates cotranslational targeting of secreted
and membrane proteins to the membrane. Targeting is regulated by GTP binding and
hydrolysis events that require direct interaction between structurally
homologous "NG" GTPase domains of the SRP signal recognition subunit
and its membrane-associated receptor, SR alpha. Structures of both the apo and
GDP bound NG domains of the prokaryotic SRP54 homolog, Ffh, and the prokaryotic
receptor homolog, FtsY, have been determined. The structural basis for the
GTP-dependent interaction between the two proteins, however, remains unknown.
RESULTS: We report here two structures of the NG GTPase of Ffh from Thermus
aquaticus bound to the nonhydrolyzable GTP analog GMPPNP. Both structures reveal
an unexpected binding mode in which the beta-phosphate is kinked away from the
binding site and magnesium is not bound. Binding of the GTP analog in the
canonical conformation found in other GTPase structures is precluded by
constriction of the phosphate binding P loop. The structural difference between
the Ffh complex and other GTPases suggests a specific conformational change that
must accompany movement of the nucleotide from an "inactive" to an
"active" binding mode. CONCLUSIONS: Conserved side chains of the
GTPase sequence motifs unique to the SRP subfamily may function to gate
formation of the active GTP bound conformation. Exposed hydrophobic residues
provide an interaction surface that may allow regulation of the GTP binding
conformation, and thus activation of the GTPase, during the association of SRP
with its receptor.
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Figure 1.
Figure 1. GMPPNP Binding to the NG DomainOmit difference
(F[o] - F[c]) electron density maps contoured at 3 s (light
blue) and 6 s (dark blue) for (a) structure N1 and (b) structure
N2a. The triplet of electron-dense peaks to the right in each
image indicates the positions of the phosphate groups. Two
residues, Gln107 and Thr112, define the top and bottom of the P
loop jaws
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The above figure is
reprinted
by permission from Cell Press:
Structure
(2001,
9,
859-867)
copyright 2001.
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