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15  structures 286  species 1  interaction 2609  sequences 25  architectures

Family: Septin (PF00735)

Summary: Septin

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Septin Edit Wikipedia article

Cell division/GTP binding protein
Identifiers
Symbol Cell_Div_GTP_bd
Pfam PF00735
Pfam clan CL0023
InterPro IPR000038

Septins are a group of highly conserved GTP binding proteins found in eukaryotes. In yeast cells, they build scaffolding to provide structural support during cell division and compartmentalize parts of the cell. Recent research in human cells suggests that septins build cages around bacterial pathogens, immobilizing the harmful microbes and preventing them from invading other cells.[1]

Septins in Saccharomyces cerevisiae[edit]

Septins in Saccharomyces cerevisiae (fluorescent micrograph)
• Green: septins (AgSEP7-GFP)
• Red: cell outline (phase contrast)
• Scale bar: 10 μm

History[edit]

The septins were discovered in 1970 by Leland H. Hartwell and colleagues in a screen for temperature-sensitive mutants affecting cell division (cdc mutants). The screen revealed four mutants which prevented cytokinesis at restrictive temperature. The corresponding genes represent the four original septins, ScCDC3, ScCDC10, ScCDC11, and ScCDC12. Despite disrupted cytokinesis, the cells continued budding, DNA synthesis, and nuclear division, which resulted in large multinucleate cells with multiple, elongated buds. In 1976, analysis of electron micrographs revealed ~20 evenly spaced striations of 10-nm filaments around the mother-bud neck in wild-type but not in septin-mutant cells. Immunofluorescence studies revealed that the septin proteins colocalize into a septin ring at the neck. The localization of all four septins is disrupted in conditional Sccdc3 and Sccdc12 mutants, indicating interdependence of the septin proteins. Strong support for this finding was provided by biochemical studies: The four original septins co-purified on affinity columns, together with a fifth septin protein, encoded by ScSEP7 or ScSHS1. Purified septins from budding yeast, Drosophila, Xenopus, and mammalian cells are able to self associate in vitro to form highly ordered, filamentous structures. How the septins interact in vitro to form heteropentamers that assemble into filaments was studied in detail in S. cerevisiae. Based on these and former studies, the septins are composed of a variable N-terminus with a basic phosphoinositide binding motif, a conserved core comprising a GTP-binding domain, a septin-unique element and a C-terminal extension including a predicted coiled coil.

Micrographs of purified filaments raised the possibility that the septins are organized in parallel to the mother-bud axis. The 10-nm striations seen on electron micrographs may be the result of lateral interaction between the filaments. Mutant strains lacking factors important for septin organization support this view. Instead of continuous rings, the septins form bars oriented along the mother-bud axis in deletion mutants of ScGIN4, ScNAP1 and ScCLA4.

Functions[edit]

Scaffold[edit]

The septins act as a scaffold, recruiting many proteins. These protein complexes are involved in cytokinesis, chitin deposition, cell polarity, spore formation, in the morphogenesis checkpoint, spindle alignment checkpoint and bud site selection.

Cytokinesis[edit]

Budding yeast cytokinesis is driven through two septin dependent, redundant processes: recruitment and contraction of the actomyosin ring and formation of the septum by vesicle fusion with the plasma membrane. In contrast to septin mutants, disruption of one single pathway only leads to a delay in cytokinesis, not complete failure of cell division. Hence, the septins are predicted to act at the most upstream level of cytokinesis.

Cell polarity[edit]

After the isotropic-apical switch in budding yeast, cortical components, supposedly of the exocyst and polarisome, are delocalized from the apical pole to the entire plasma membrane of the bud, but not the mother cell. The septin ring at the neck serves as a cortical barrier that prevents membrane diffusion of these factors between the two compartments. This asymmetric distribution is abolished in septin mutants.

Some conditional septin mutants do not form buds at their normal axial location. Moreover, the typical localization of some bud-site-selection factors in a double ring at the neck is lost or disturbed in these mutants. This indicates that the septins may serve as anchoring site for such factors in axially budding cells.

Organization[edit]

It seems that one single septin organization should not be sufficient to fulfill such a variety of tasks. Accordingly, the septin cortex undergoes several changes throughout the cell cycle: The first visible septin structure is a distinct ring which appears ~15 min before bud emergence. After bud emergence, the ring broadens to assume the shape of an hourglass around the mother-bud neck. During cytokinesis, the septin cortex splits into a double ring which eventually disappears. How can the septin cortex undergo such dramatic changes, although some of its functions may require it to be a stable structure? FRAP analysis has revealed that the turnover of septins at the neck undergoes multiple changes during the cell cycle. The predominant, functional conformation is characterized by a low turnover rate (frozen state), during which the septins are phosphorylated. Structural changes require a destabilization of the septin cortex (fluid state) induced by dephosphorylation prior to bud emergence, ring splitting and cell separation.

The composition of the septin cortex does not only vary throughout the cell cycle but also along the mother-bud axis. This inherent polarity of septin filaments allows concentration of some proteins primarily to the mother side of the neck, some to the center and others to the bud site.

Septins in filamentous fungi[edit]

Since their discovery in S. cerevisiae, septin homologues have been found throughout the eukaryotic kingdom, with the exception of plants. The variety of different shapes that septins can assume within a single cell is especially apparent in filamentous fungi, where they control aspects of filamentous morphology.

Candida albicans[edit]

The genome of C. albicans encodes homologues to all S. cerevisiae septins (CaCDC3, CaCDC10, CaCDC11, CaCDC12, CaSEP7). They form a diffuse band at the base of emerging hyphae, a bright double ring at septation sites, an extended diffuse cap at hyphal tips and elongated filaments stretching around the spherical chlamydospores. As an effect of maturation, double rings reflect hyphal polarity by disassembling the tip proximal ring. CaCdc3p and CaCdc12p are essential for proliferation in yeast or hyphal forms. Cacdc10Δ and Cacdc11Δ deletion mutants are viable but show aberrant chitin localization and cannot properly maintain hyphal growth direction.

Aspergillus nidulans[edit]

Five septins are found in A. nidulans (AnAspAp, AnAspBp, AnAspCp, AnAspDp, AnAspEp). AnAspBp forms single rings at septation sites that eventually split into double rings. Additionally, AnAspBp forms a ring at sites of branch emergence which broadens into a band as the branch grows. Like in C. albicans, double rings reflect polarity of the hypha, but by disassembling the more basal ring. Bases for the various patterns of septin organization could be different modifications and/or localization of different septin interaction partners. Conditional mutants of the essential AnAspBp display diffuse chitin deposition and a hyper-branching phenotype.

Ashbya gossypii[edit]

Septins in Ashbya gossypii (fluorescent micrograph) • Green: septins (AgSEP7-GFP)
• Red: cell outline (phase contrast)
• Inlay: 3D reconstruction of a discontinuous septin ring
• Scale bars: 10 μm

The ascomycete A. gossypii possesses homologues to all S. cerevisiae septins, with one being duplicated (AgCDC3, AgCDC10, AgCDC11A, AgCDC11B, AgCDC12, AgSEP7). In vivo studies of AgSep7p-GFP have revealed that septins assemble into discontinuous hyphal rings close to growing tips and sites of branch formation and into asymmetric structures at the base of branching points. Rings are made of filaments which are long and diffuse close to growing tips and short and compact further away from the tip. During septum formation, the septin ring splits into two to form a double ring. Agcdc3Δ, Agcdc10Δ and Agcdc12Δ deletion mutants display aberrant morphology and are defective for actin-ring formation, chitin-ring formation, and sporulation. Due to the lack of septa, septin deletion mutants are highly sensitive, and damage of a single hypha can result into complete lysis of a young mycelium.

Human septins[edit]

Most studies of septins, or guanosine-5′-triphosphate (GTP) binding proteins, have been confined to yeast cells. The latest research in human cells suggests that septins build 'cages' around bacterial pathogens, immobilizing the harmful microbes and preventing them from invading other healthy cells. This cellular defence system could be explored to create therapies for dysentery and other illnesses. “This is a new way for cells to control an infection,” Shigella, a bacterium that causes sometimes lethal diarrhoea in humans and other primates. To propagate from cell to cell, Shigella bacteria develop actin-polymer 'tails', which propel the microbes around and allow them to force their way into neighbouring host cells. To counterattack, human cells produce a cell-signalling protein called TNF-α. The researchers found that when TNF-α is present, thick bundles of septin filaments encircle the microbes. This, in turn, interferes with tail formation and stops Shigella in its tracks. Microbes that become trapped in septin cages are broken down in a stage of the cell's life cycle called autophagy. “Autophagy is more efficient because of the septin cage, and the septin cage does not occur if you do not have the autophagy. Many research groups are working on understand the link between septins and autophagy, and to determine how important septins are in humans in vivo. Disruptions in septins and mutations in the genes that code for them could be involved in causing leukaemia, colon cancer and neurodegenerative conditions such as Parkinson's disease and Alzheimer's disease. Potential therapies for these, as well as for bacterial conditions such as dysentery caused by Shigella, might bolster the body’s immune system with drugs that mimic the behaviour of TNF-α and allow the septin cages to proliferate.[1]

In mitochondria[edit]

The septin localized in the mitochondria is called mitochondrial septin (M-septin). It was identified as a CRMP/CRAM-interacting protein in developing mouse brain.[2]

References[edit]

  1. ^ a b Mascarelli A (December 2011). "Septin proteins take bacterial prisoners: A cellular defence against microbial pathogens holds therapeutic potential". Nature. doi:10.1038/nature.2011.9540. 
  2. ^ Takahashi S, Inatome R, Yamamura H, Yanagi S (February 2003). "Isolation and expression of a novel mitochondrial septin that interacts with CRMP/CRAM in the developing neurones". Genes Cells 8 (2): 81–93. doi:10.1046/j.1365-2443.2003.00617.x. PMID 12581152. 

Further reading[edit]

This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.

Septin Provide feedback

Members of this family include CDC3, CDC10, CDC11 and CDC12/Septin. Members of this family bind GTP. As regards the septins, these are polypeptides of 30-65kDa with three characteristic GTPase motifs (G-1, G-3 and G-4) that are similar to those of the Ras family. The G-4 motif is strictly conserved with a unique septin consensus of AKAD. Most septins are thought to have at least one coiled-coil region, which in some cases is necessary for intermolecular interactions that allow septins to polymerise to form rod-shaped complexes. In turn, these are arranged into tandem arrays to form filaments. They are multifunctional proteins, with roles in cytokinesis, sporulation, germ cell development, exocytosis and apoptosis [2].

Literature references

  1. Casamayor A, Snyder M; , Mol Cell Biol 2003;23:2762-2777.: Molecular dissection of a yeast septin: distinct domains are required for septin interaction, localization, and function. PUBMED:12665577 EPMC:12665577

  2. Kinoshita M; , Genome Biol 2003;4:236.: The septins. PUBMED:14611653 EPMC:14611653


External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR000038

Septins constitute a eukaryotic family of guanine nucleotide-binding proteins, most of which polymerise to form filaments [PUBMED:14611653]. Members of the family were first identified by genetic screening for Saccharomyces cerevisiae (Baker's yeast) mutants defective in cytokinesis [PUBMED:4950437]. Temperature-sensitive mutations in four genes, CDC3, CDC10, CDC11 and CDC12, were found to cause cell-cycle arrest and defects in bud growth and cytokinesis. The protein products of these genes localise at the division plane between mother and daughter cells, indicating a role in mother-daughter separation during cytokinesis [PUBMED:3316985]. Members of the family were therefore termed septins to reflect their role in septation and cell division. The identification of septin homologues in higher eukaryotes, which localise to the cleavage furrow in dividing cells, supports an orthologous function in cytokinesis. Septins have since been identified in most eukaryotes, except plants [PUBMED:10805747].

Septins are approximately 40-50 kDa in molecular mass, and typically comprise a conserved central core domain (more than 35% sequence identity between mammalian and yeast homologues) flanked by more divergent N- and C-termini. Most septins possess a P-loop motif in their N-terminal domain (which is characteristic of GTP-binding proteins), and a predicted C-terminal coiled-coil domain [PUBMED:10481176].

A number of septin interaction partners have been identified in yeast, many of which are components of the budding site selection machinery, kinase cascades or of the ubiquitination pathway. It has been proposed that septins may act as a scaffold that provides an interaction matrix for other proteins [PUBMED:10805747, PUBMED:10481176]. In mammals, septins have been shown to regulate vesicle dynamics [PUBMED:11942624]. Mammalian septins have also been implicated in a variety of other cellular processes, including apoptosis, carcinogenesis and neurodegeneration [PUBMED:9203580].

This entry represents a variety of septins and homologous sequences involved in the cell division process.

Gene Ontology

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Domain organisation

Below is a listing of the unique domain organisations or architectures in which this domain is found. More...

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Pfam Clan

This family is a member of clan P-loop_NTPase (CL0023), which has the following description:

AAA family proteins often perform chaperone-like functions that assist in the assembly, operation, or disassembly of protein complexes [2].

The clan contains the following 198 members:

6PF2K AAA AAA-ATPase_like AAA_10 AAA_11 AAA_12 AAA_13 AAA_14 AAA_15 AAA_16 AAA_17 AAA_18 AAA_19 AAA_2 AAA_21 AAA_22 AAA_23 AAA_24 AAA_25 AAA_26 AAA_27 AAA_28 AAA_29 AAA_3 AAA_30 AAA_31 AAA_32 AAA_33 AAA_34 AAA_35 AAA_4 AAA_5 AAA_6 AAA_7 AAA_8 AAA_9 AAA_PrkA ABC_ATPase ABC_tran ABC_tran_2 Adeno_IVa2 Adenylsucc_synt ADK AFG1_ATPase AIG1 APS_kinase Arch_ATPase Arf ArgK ArsA_ATPase ATP-synt_ab ATP_bind_1 ATP_bind_2 Bac_DnaA CbiA CMS1 CoaE CobA_CobO_BtuR CobU cobW CPT CTP_synth_N Cytidylate_kin Cytidylate_kin2 DAP3 DEAD DEAD_2 DLIC DNA_pack_C DNA_pack_N DNA_pol3_delta DNA_pol3_delta2 DnaB_C dNK DUF1253 DUF1611 DUF2075 DUF2478 DUF258 DUF2791 DUF2813 DUF3584 DUF463 DUF815 DUF853 DUF87 DUF927 Dynamin_N Exonuc_V_gamma FeoB_N Fer4_NifH Flavi_DEAD FTHFS FtsK_SpoIIIE G-alpha Gal-3-0_sulfotr GBP GTP_EFTU GTP_EFTU_D2 GTP_EFTU_D4 Gtr1_RagA Guanylate_kin GvpD HDA2-3 Helicase_C Helicase_C_2 Helicase_C_4 Helicase_RecD Herpes_Helicase Herpes_ori_bp Herpes_TK IIGP IPPT IPT IstB_IS21 KaiC KAP_NTPase Kinesin Kinesin-relat_1 Kinesin-related KTI12 LpxK MCM MEDS Mg_chelatase Mg_chelatase_2 MipZ Miro MMR_HSR1 MobB MukB MutS_V Myosin_head NACHT NB-ARC NOG1 NTPase_1 ParA Parvo_NS1 PAXNEB PduV-EutP PhoH PIF1 Podovirus_Gp16 Polyoma_lg_T_C Pox_A32 PPK2 PPV_E1_C PRK Rad17 Rad51 Ras RecA ResIII RHD3 RHSP RNA12 RNA_helicase RuvB_N SbcCD_C SecA_DEAD Septin Sigma54_activ_2 Sigma54_activat SKI SMC_N SNF2_N Spore_IV_A SRP54 SRPRB Sulfotransfer_1 Sulfotransfer_2 Sulfotransfer_3 Sulphotransf T2SE T4SS-DNA_transf Terminase_1 Terminase_3 Terminase_6 Terminase_GpA Thymidylate_kin TIP49 TK TniB Torsin TraG-D_C tRNA_lig_kinase TrwB_AAD_bind UPF0079 UvrD-helicase UvrD_C UvrD_C_2 Viral_helicase1 VirC1 VirE YhjQ Zeta_toxin Zot

Alignments

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(14)
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(2609)
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Meta
(269)
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(422)
RP35
(705)
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(1111)
RP75
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  Seed
(14)
Full
(2609)
Representative proteomes NCBI
(3139)
Meta
(269)
RP15
(422)
RP35
(705)
RP55
(1111)
RP75
(1492)
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  Seed
(14)
Full
(2609)
Representative proteomes NCBI
(3139)
Meta
(269)
RP15
(422)
RP35
(705)
RP55
(1111)
RP75
(1492)
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Gzipped Download   Download   Download   Download   Download   Download   Download   Download  

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Pfam alignments:

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Curation and family details

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Curation View help on the curation process

Seed source: Pfam-B_440 (release 2.1)
Previous IDs: GTP_CDC;
Type: Family
Author: Bateman A
Number in seed: 14
Number in full: 2609
Average length of the domain: 234.50 aa
Average identity of full alignment: 37 %
Average coverage of the sequence by the domain: 62.73 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 20.0 20.0
Trusted cut-off 20.0 20.0
Noise cut-off 19.9 19.9
Model length: 281
Family (HMM) version: 13
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Species distribution

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Interactions

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Septin

Structures

For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Septin domain has been found. There are 15 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.

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