{PDOC51719}
{PS51719; G_SEPTIN}
{BEGIN}
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* Septin-type guanine nucleotide-binding (G) domain profile *
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The P-loop  (see  <PDOC00017>)  guanosine  triphosphatases (GTPases) control a
multitude of  biological  processes, ranging from cell division, cell cycling,
and signal  transduction,  to ribosome assembly and protein synthesis. GTPases
exert their  control  by interchanging between an inactive GDP-bound state and
an active  GTP-bound  state,  thereby acting as molecular switches. The common
denominator of  GTPases is the highly conserved guanine nucleotide-binding (G)
domain that is responsible for binding and hydrolysis of guanine nucleotides.

Septins are a family of eukaryotic cytoskeletal proteins conserved from yeasts
to humans.  The  septin  family belongs to the guanosine-triphosphate (GTP)ase
superclass of P-loop nucleoside triphosphate (NTP)ases. Septins participate in
diverse cellular functions including cytokinesis, vesicle trafficking, vesicle
fusion, axonal   guidance   and   migration,   diffusion  barrier,  scaffolds,
pathogenesis and  others.  Septin  monomers  form  homo- and hetero-oligomeric
complexes that  assemble  into filaments. Structurally all septins have a GTP-
binding domain  flanked  by  N- and C-terminal regions of variable length. The
GTP-binding domain  is  the  most highly conserved and is characterized by the
presence of  three  of the five classical GTP-binding motifs. The G1 motif (or
Walker A  box, GxxxxGKS/T) forms the P-loop, which interacts directly with the
nucleotide, whereas  the  G3  (DxxG)  and  G4  (xKxD)  motifs are respectively
essential for  Mg(2+)  binding and for conferring GTP binding specificity over
other nucleotides.  The  basic  structure  of the septin-type G domain closely
resembles the canonical G domain exemplified by Ras, with six beta-strands and
five alpha-helices.  A  unique  feature  of  the  septin-type  G domain is the
presence of  four  additional elements compared to Ras (see <PDB:2QA5>). These
are the  helix  alpha5' between alpha4 and beta6, the two antiparallel strands
beta7 and  beta8,  and the alpha6 C-terminal helix that points away from the G
domain at  a  90°  angle  relative to the axis of interaction between subunits
[1,2,3,4,5].

The profile we developed covers the entire septin-type G domain.

-Sequences known to belong to this class detected by the profile: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.
-Last update: May 2014 / First entry.

[ 1] Leipe D.D., Wolf Y.I., Koonin E.V., Aravind L.
     "Classification and evolution of P-loop GTPases and related ATPases."
     J. Mol. Biol. 317:41-72(2002).
     PubMed=11916378; DOI=10.1006/jmbi.2001.5378
[ 2] Versele M., Thorner J.
     "Some assembly required: yeast septins provide the instruction
     manual."
     Trends Cell Biol. 15:414-424(2005).
     PubMed=16009555; DOI=10.1016/j.tcb.2005.06.007
[ 3] Sirajuddin M., Farkasovsky M., Hauer F., Kuehlmann D., Macara I.G.,
     Weyand M., Stark H., Wittinghofer A.
     "Structural insight into filament formation by mammalian septins."
     Nature 449:311-315(2007).
     PubMed=17637674; DOI=10.1038/nature06052
[ 4] Macedo J.N.A:, Valadares N.F., Marques I.A., Ferreira F.M.,
     Damalio J.C.P., Pereira H.M., Garratt R.C., Araujo A.P.U.
     "The structure and properties of septin 3: a possible missing link in
     septin filament formation."
     Biochem. J. 450:95-105(2013).
     PubMed=23163726; DOI=10.1042/BJ20120851
[ 5] Zeraik A.E., Rinaldi G., Mann V.H., Popratiloff A., Araujo A.P.U.,
     Demarco R., Brindley P.J.
     "Septins of Platyhelminths: identification, phylogeny, expression and
     localization among developmental stages of Schistosoma mansoni."
     PLoS Negl. Trop. Dis. 7:E2602-E2602(2013).
     PubMed=24367716; DOI=10.1371/journal.pntd.0002602

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