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PDBsum entry 5irr
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References listed in PDB file
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Key reference
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Title
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Filaments and fingers: novel structural aspects of the single septin fromchlamydomonas reinhardtii.
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Authors
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A.P.A.Pinto,
H.M.Pereira,
A.E.Zeraik,
H.Ciol,
F.M.Ferreira,
J.Brandão-Neto,
R.Demarco,
M.V.A.S.Navarro,
C.Risi,
V.E.Galkin,
R.C.Garratt,
A.P.U.Araujo.
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Ref.
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J Biol Chem, 2017,
292,
10899-10911.
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PubMed id
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Abstract
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Septins are filament-forming GTP-binding proteins involved in many essential
cellular events related to cytoskeletal dynamics and maintenance. Septins can
self-assemble into heterocomplexes, which polymerize into highly organized, cell
membrane-interacting filaments. The number of septin genes varies among
organisms, and although their structure and function have been thoroughly
studied in opisthokonts (including animals and fungi), no structural studies
have been reported for other organisms. This makes the single septin
fromChlamydomonas(CrSEPT) a particularly attractive model for
investigating whether functional homopolymeric septin filaments also exist.
CrSEPT was detected at the base of the flagella inChlamydomonas,
suggesting that CrSEPT is involved in the formation of a membrane-diffusion
barrier. Using transmission electron microscopy, we observed that recombinant
CrSEPT forms long filaments with dimensions comparable with those of the
canonical structure described for opisthokonts. The GTP-binding domain of CrSEPT
purified as a nucleotide-free monomer that hydrolyzes GTP and readily binds its
analog guanosine 5'-3-O-(thio)triphosphate. We also found that upon
nucleotide binding, CrSEPT formed dimers that were stabilized by an interface
involving the ligand (G-interface). Across this interface, one monomer supplied
a catalytic arginine to the opposing subunit, greatly accelerating the rate of
GTP hydrolysis. This is the first report of an arginine finger observed in a
septin and suggests that CrSEPT may act as its own GTP-activating protein. The
finger is conserved in all algal septin sequences, suggesting a possible
correlation between the ability to form homopolymeric filaments and the
accelerated rate of hydrolysis that it provides.
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