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19  structures 1457  species 0  interactions 6315  sequences 147  architectures

Family: Sad1_UNC (PF07738)

Summary: Sad1 / UNC-like C-terminal

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This is the Wikipedia entry entitled "SUN domain". More...

SUN domain Edit Wikipedia article

Symbol Sad1_UNC
Pfam PF07738
Pfam clan CL0202
InterPro IPR012919

SUN (Sad1p, UNC-84) domains are conserved C-terminal protein regions a few hundred amino acids long. SUN domains are usually found following a transmembrane domain and a less conserved region of amino acids. Most proteins containing SUN domains are thought to be involved in the positioning of the nucleus in the cell. It is thought that SUN domains interact directly with KASH domains in the space between the outer and inner nuclear membranes to bridge the nuclear envelope and transfer force from the nucleoskeleton to the cytoplasmic cytoskeleton which enables mechanosensory roles in cells.[1] SUN proteins are thought to localize to the inner nuclear membrane.[2] The S. pombe Sad1 protein localises at the spindle pole body. In mammals, the SUN domain is present in two proteins, Sun1 and Sun2. The SUN domain of Sun2 has been demonstrated to be in the periplasm.[3][4]

Examples of SUN Proteins

Caenorhabditis elegans

  • SUN-1/matefin
  • UNC-84

Drosophila melanogaster

  • Klaroid
  • Spag4


Schizosaccharomyces pombe

  • Sad1p

Saccharomyces cerevisiae

  • Mps3p


  • SUN1, SUN2, SUN3, SUN4, SUN5


  • SUN1, SUN2


  1. ^ Uzer G, Thompson WR, Sen B, Xie Z, Yen SS, Miller S, Bas G, Styner M, Rubin CT, Judex S, Burridge K, Rubin J (June 2015). "Cell Mechanosensitivity to Extremely Low-Magnitude Signals Is Enabled by a LINCed Nucleus". Stem Cells. 33 (6): 2063–76. doi:10.1002/stem.2004. PMC 4458857Freely accessible. PMID 25787126. 
  2. ^ Tzur YB, Wilson KL, Gruenbaum Y (October 2006). "SUN-domain proteins: 'Velcro' that links the nucleoskeleton to the cytoskeleton". Nature Reviews. Molecular Cell Biology. 7 (10): 782–8. doi:10.1038/nrm2003. PMID 16926857. 
  3. ^ Hodzic DM, Yeater DB, Bengtsson L, Otto H, Stahl PD (June 2004). "Sun2 is a novel mammalian inner nuclear membrane protein". The Journal of Biological Chemistry. 279 (24): 25805–12. doi:10.1074/jbc.M313157200. PMID 15082709. 
  4. ^ Raff JW (September 1999). "The missing (L) UNC?". Current Biology. 9 (18): R708–10. doi:10.1016/S0960-9822(99)80446-1. PMID 10508607. 

This article incorporates text from the public domain Pfam and InterPro IPR012919

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.

Sad1 / UNC-like C-terminal Provide feedback

The C. elegans UNC-84 protein is a nuclear envelope protein that is involved in nuclear anchoring and migration during development. The S. pombe Sad1 protein localises at the spindle pole body. UNC-84 and and Sad1 share a common C-terminal region, that is often termed the SUN (Sad1 and UNC) domain [1-2]. In mammals, the SUN domain is present in two proteins, Sun1 and Sun2 [1]. The SUN domain of Sun2 has been demonstrated to be in the periplasm [2].

Literature references

  1. Raff JW; , Curr Biol 1999;9:708-710.: The missing (L) UNC?. PUBMED:10508607 EPMC:10508607

  2. Hodzic DM, Yeater DB, Bengtsson L, Otto H, Stahl PD; , J Biol Chem 2004;279:25805-25812.: Sun2 is a novel mammalian inner nuclear membrane protein. PUBMED:15082709 EPMC:15082709

Internal database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR012919

Sad1/UNC-84 (SUN)-domain proteins are inner nuclear membrane (INM) proteins that are part of bridging complexes linking cytoskeletal elements with the nucleoskeleton. Originaly identified based on an ~150-amino acid region of homology between the C terminus of the Schizosaccharomyces pombe Sad1 protein and the Caenorhabditis elegans UNC-84 protein, SUN proteins are present in the proteomes of most eucaryotes. In addition to the SUN domain, these proteins contain a transmembrane sequence and at least one coiled-coil domain and localise to the inner nuclear envelope. SUN proteins are anchored in the inner nuclear envelope by their transmembrane segment and oriented in the membrane such that the C-terminal SUN domain is located in the space between the inner and outer nuclear membrane. Here, the SUN domain can interact with the C- terminal tail of an outer nuclear envelope protein that binds to the cytoskeleton, including the centrosome [ PUBMED:15611647 , PUBMED:16923827 , PUBMED:19807882 ].

Some proteins known to contain a SUN domain are listed below:

  • Fission yeast spindle pole body-associated protein Sad1.
  • Yeast spindle pole body assembly component MPS3, essential for nuclear division and fusion.
  • Yeast uncharacterised protein SLP1.
  • Caenorhabditis nuclear migration and anchoring protein UNC-84.
  • Caenorhabditis SUN domain-containing protein 1 (sun-1), involved in centrosome attachment to the nucleus.
  • Mammalian sperm-associated antigen 4 protein (SPAG4), may assist the organisation and assembly of outer dense fibres (ODFs), a specific structure of the sperm tail.
  • Mammalian sperm-associated antigen 4-like protein (SPAG4L).
  • Mammalian SUN1.
  • Mammalian SUN2.
  • Mammalian SUN3.

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 GBD (CL0202), which has the following description:

This large superfamily contains beta sandwich domains with a jelly roll topology. Many of these families are involved in carbohydrate recognition. Despite sharing little sequence similarity they do share a weak sequence motif, with a conserved bulge in the C-terminal beta sheet. The probable role of this bulge is in bending of the beta sheet that contains the bulge. This enables the curvature of the sheet forming the sugar binding site [1].

The clan contains the following 70 members:

7TMR-DISMED2 Agarase_CBM Allantoicase ANAPC10 Arabino_trans_C Bac_rhamnosid_N BcsB BetaGal_dom4_5 BPA_C Calpain_III CBM-like CBM27 CBM32 CBM46 CBM60 CBM65_1 CBM_11 CBM_15 CBM_17_28 CBM_26 CBM_35 CBM_4_9 CBM_6 CE2_N CIA30 Clenterotox Cry1Ac_D5 DUF4465 DUF4627 DUF5000 DUF5010_C DUF5077 DUF5625 DUF642 Endotoxin_C Ephrin_lbd Exop_C F5_F8_type_C FBA FlhE GH101_N GH115_C Glft2_N Glyco_hydro_2_N GxDLY HA70_C Laminin_B Laminin_N Lectin_like Lipl32 Lyase_N Malectin Malectin_like Muskelin_N NPCBM P_proprotein PA-IL PAW PCMD PepX_C PINIT PITH PPC PulA_N1 Sad1_UNC SGBP_B_XBD TcA_TcB_BD Thioredoxin_10 XRCC1_N YpM


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Curation and family details

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Curation View help on the curation process

Seed source: Pfam-B_5052 (release 14.0)
Previous IDs: none
Type: Family
Sequence Ontology: SO:0100021
Author: Wood V , Finn RD
Number in seed: 23
Number in full: 6315
Average length of the domain: 122.10 aa
Average identity of full alignment: 24 %
Average coverage of the sequence by the domain: 14.95 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 57096847 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 20.7 20.7
Trusted cut-off 20.7 20.7
Noise cut-off 20.6 20.6
Model length: 131
Family (HMM) version: 15
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Species distribution

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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 Sad1_UNC domain has been found. There are 19 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 sequence.

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