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PDBsum entry 1ffh
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Ribonucleoprotein
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PDB id
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1ffh
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References listed in PDB file
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Key reference
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Title
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Structure of the conserved gtpase domain of the signal recognition particle.
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Authors
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D.M.Freymann,
R.J.Keenan,
R.M.Stroud,
P.Walter.
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Ref.
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Nature, 1997,
385,
361-364.
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PubMed id
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Abstract
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The signal-recognition particle (SRP) and its receptor (SR) function in the
co-translational targeting of nascent protein-ribosome complexes to the membrane
translocation apparatus. The SRP protein subunit (termed Ffh in bacteria) that
recognizes the signal sequence of nascent polypeptides is a GTPase, as is the
SR-alpha subunit (termed FtsY). Ffh and FtsY interact directly, each stimulating
the GTP hydrolysis activity of the other. The sequence of Ffh suggests three
domains: an amino-terminal N domain of unknown function, a central GTPase G
domain, and a methionine-rich M domain that binds both SRP RNA and signal
peptides. Sequence conservation suggests that structurally similar N and G
domains are present in FtsY. Here we report the structure of the nucleotide-free
form of the NG fragment of Ffh. Consistent with a role for apo Ffh in protein
targeting, the side chains of the empty active-site pocket form a tight network
of interactions which may stabilize the nucleotide-free protein. The structural
relationship between the two domains suggests that the N domain senses or
controls the nucleotide occupancy of the GTPase domain. A structural subdomain
unique to these evolutionarily conserved GTPases constitutes them as a distinct
subfamily in the GTPase superfamily.
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