
4  structures 464  species 0  interactions 514  sequences 2  architectures

Family: DUF4426 (PF14467)

Summary: Domain of unknown function (DUF4426)


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Domain of unknown function Edit Wikipedia article

A domain of unknown function (DUF) is a protein domain that has no characterised function. These families have been collected together in the Pfam database using the prefix DUF followed by a number, with examples being DUF2992 and DUF1220. As of 2019, there are almost 4,000 DUF families within the Pfam database representing over 22% of known families. Some DUFs are not named using the nomenclature due to popular usage but are nevertheless DUFs.[1]

The DUF designation is tentative, and such families tend to be renamed to a more specific name (or merged to an existing domain) after a function is identified.[2][3]


The DUF naming scheme was introduced by Chris Ponting, through the addition of DUF1 and DUF2 to the SMART database.[4] These two domains were found to be widely distributed in bacterial signaling proteins. Subsequently, the functions of these domains were identified and they have since been renamed as the GGDEF domain and EAL domain respectively.[2]


Structural genomics programmes have attempted to understand the function of DUFs through structure determination. The structures of over 250 DUF families have been solved. This (2009) work showed that about two thirds of DUF families had a structure similar to a previously solved one and therefore likely to be divergent members of existing protein superfamilies, whereas about one third possessed a novel protein fold.[5]

Some DUF families share remote sequence homology with domains that has characterized function. Computational work can be used to link these relationships. An 2015 work was able to assign 20% of the DUFs to characterized structual superfamilies.[6] Pfam also continuously perform the (manually-verified) assignment in "clan" superfamily entries.[1]

Frequency and conservation

Protein domains and DUFs in different domains of life. Left: Annotated domains. Right: domains of unknown function. Not all overlaps shown.[7]

More than 20% of all protein domains were annotated as DUFs in 2013. About 2,700 DUFs are found in bacteria compared with just over 1,500 in eukaryotes. Over 800 DUFs are shared between bacteria and eukaryotes, and about 300 of these are also present in archaea. A total of 2,786 bacterial Pfam domains even occur in animals, including 320 DUFs.[7]

Role in biology

Many DUFs are highly conserved, indicating an important role in biology. However, many such DUFs are not essential, hence their biological role often remains unknown. For instance, DUF143 is present in most bacteria and eukaryotic genomes.[8] However, when it was deleted in Escherichia coli no obvious phenotype was detected. Later it was shown that the proteins that contain DUF143, are ribosomal silencing factors that block the assembly of the two ribosomal subunits.[8] While this function is not essential, it helps the cells to adapt to low nutrient conditions by shutting down protein biosynthesis. As a result, these proteins and the DUF only become relevant when the cells starve.[8] It is thus believed that many DUFs (or proteins of unknown function, PUFs) are only required under certain conditions.

Essential DUFs

Goodacre et al. identified 238 DUFs in 355 essential proteins (in 16 model bacterial species), most of which represent single-domain proteins, clearly establishing the biological essentiality of DUFs. These DUFs are called "essential DUFs" or eDUFs.[7]

External links


  1. ^ a b El-Gebali S, Mistry J, Bateman A, Eddy SR, Luciani A, Potter SC, Qureshi M, Richardson LJ, Salazar GA, Smart A, Sonnhammer EL, Hirsh L, Paladin L, Piovesan D, Tosatto SC, Finn RD (January 2019). "The Pfam protein families database in 2019". Nucleic Acids Research. 47 (D1): D427â€“D432. doi:10.1093/nar/gky995. PMC 6324024. PMID 30357350.
  2. ^ a b Bateman A, Coggill P, Finn RD (October 2010). "DUFs: families in search of function". Acta Crystallographica. Section F, Structural Biology and Crystallization Communications. 66 (Pt 10): 1148â€“52. doi:10.1107/S1744309110001685. PMC 2954198. PMID 20944204.
  3. ^ Punta M, Coggill PC, Eberhardt RY, Mistry J, Tate J, Boursnell C, Pang N, Forslund K, Ceric G, Clements J, Heger A, Holm L, Sonnhammer EL, Eddy SR, Bateman A, Finn RD (January 2012). "The Pfam protein families database". Nucleic Acids Research. 40 (Database issue): D290â€“301. doi:10.1093/nar/gkr1065. PMC 3245129. PMID 22127870.
  4. ^ Schultz J, Milpetz F, Bork P, Ponting CP (May 1998). "SMART, a simple modular architecture research tool: identification of signaling domains". Proceedings of the National Academy of Sciences of the United States of America. 95 (11): 5857â€“64. Bibcode:1998PNAS...95.5857S. doi:10.1073/pnas.95.11.5857. PMC 34487. PMID 9600884.
  5. ^ Jaroszewski L, Li Z, Krishna SS, Bakolitsa C, Wooley J, Deacon AM, Wilson IA, Godzik A (September 2009). "Exploration of uncharted regions of the protein universe". PLoS Biology. 7 (9): e1000205. doi:10.1371/journal.pbio.1000205. PMC 2744874. PMID 19787035.
  6. ^ Mudgal R, Sandhya S, Chandra N, Srinivasan N (July 2015). "De-DUFing the DUFs: Deciphering distant evolutionary relationships of Domains of Unknown Function using sensitive homology detection methods". Biology Direct. 10 (1): 38. doi:10.1186/s13062-015-0069-2. PMC 4520260. PMID 26228684.
  7. ^ a b c Goodacre NF, Gerloff DL, Uetz P (December 2013). "Protein domains of unknown function are essential in bacteria". mBio. 5 (1): e00744â€“13. doi:10.1128/mBio.00744-13. PMC 3884060. PMID 24381303.
  8. ^ a b c HÃ¤user R, Pech M, Kijek J, Yamamoto H, Titz B, Naeve F, Tovchigrechko A, Yamamoto K, Szaflarski W, Takeuchi N, Stellberger T, Diefenbacher ME, Nierhaus KH, Uetz P (2012). Hughes D (ed.). "RsfA (YbeB) proteins are conserved ribosomal silencing factors". PLoS Genetics. 8 (7): e1002815. doi:10.1371/journal.pgen.1002815. PMC 3400551. PMID 22829778.


"DUF" families are annotated with the Domain of unknown function Wikipedia article. This is a general article, with no specific information about individual Pfam DUFs. If you have information about this particular DUF, please let us know using the "Add annotation" button below.

Domain of unknown function (DUF4426) Provide feedback

Members of this entry are found mostly in g-proteobacteria, especially in Vibrio. Strangely enough, there seems to be one eukaryotic homolog in Nematostella vectensis (NEMVEDRAFT_v1g226006), where the PA0388-like domain is fused with a domain homogous to the Methionine biosynthesis protein MetW (see below). In several Pseudomonas species, but also in Vibrio vulnificus and Azotobacter vinelandii PA0388 homologs are genomic neighbors of Nucleoside 5-triphosphatase RdgB (dHAPTP, dITP, XTP-specific) (EC and Methionine biosynthesis protein MetW. On the other hand, in most Vibrio species it appears as a part of a conserved operon involved in possible response to stress.

This tab holds annotation information from the InterPro database.

InterPro entry IPR025218

This presumed domain is functionally uncharacterised.

Domain organisation


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Pfam Clan

This family is a member of clan E-set (CL0159), which has the following description:

This clan includes a diverse range of domains that have an Ig-like fold and appear to be distantly related to each other. The clan includes: PKD domains, cadherins and several families of bacterial Ig-like domains as well as viral tail fibre proteins. it also includes several Fibronectin type III domain-containing families.

The clan contains the following 238 members:

A2M A2M_BRD A2M_recep AA9 Adeno_GP19K AlcCBM31 Alpha-amylase_N Alpha_adaptinC2 Alpha_E2_glycop Anth_Ig Arch_flagellin aRib Arylsulfotran_N ASF1_hist_chap ATG19 BACON BACON_2 BatD BIg21 Big_1 Big_10 Big_11 Big_12 Big_13 Big_2 Big_3 Big_3_2 Big_3_3 Big_3_4 Big_3_5 Big_4 Big_5 Big_6 Big_7 Big_8 Big_9 Bile_Hydr_Trans BiPBP_C bMG1 bMG10 bMG3 bMG5 bMG6 BslA BsuPI Cadherin Cadherin-like Cadherin_2 Cadherin_3 Cadherin_4 Cadherin_5 Cadherin_pro CagX Calx-beta Candida_ALS_N CARDB CBM39 CBM_X2 CD45 CelD_N Ceramidse_alk_C CHB_HEX_C CHB_HEX_C_1 ChitinaseA_N ChiW_Ig_like Chlam_OMP6 CHU_C Coatamer_beta_C COP-gamma_platf CopC CshA_repeat Cyc-maltodext_N Cytomega_US3 DsbC DUF11 DUF1410 DUF1425 DUF1929 DUF2271 DUF3244 DUF3327 DUF3416 DUF3458 DUF3501 DUF3823_C DUF3859 DUF4165 DUF4179 DUF4426 DUF4469 DUF4625 DUF4879 DUF4959 DUF4981 DUF4982 DUF4998 DUF5001 DUF5008 DUF5011 DUF5065 DUF5115 DUF525 DUF5643 DUF6383 DUF916 EB_dh ECD EpoR_lig-bind ERAP1_C EstA_Ig_like Expansin_C Filamin FixG_C Flavi_glycop_C FlgD_ig fn3 Fn3-like fn3_2 fn3_4 fn3_5 fn3_6 FN3_7 Fn3_assoc fn3_PAP GBS_Bsp-like Glucodextran_B Glyco_hydro2_C5 Glyco_hydro_2 Gmad2 GMP_PDE_delta GPI-anchored Hanta_G1 He_PIG HECW_N HemeBinding_Shp Hemocyanin_C Herpes_BLLF1 HYR IFNGR1 Ig_GlcNase Ig_mannosidase IL12p40_C Il13Ra_Ig IL17R_fnIII_D1 IL17R_fnIII_D2 IL2RB_N1 IL3Ra_N IL4Ra_N IL6Ra-bind Inhibitor_I42 Inhibitor_I71 InlK_D3 Integrin_alpha2 Interfer-bind Invasin_D3 IRK_C IrmA Iron_transport LEA_2 Lep_receptor_Ig LIFR_N Lipase_bact_N LPMO_10 LRR_adjacent LTD Mannosidase_ig MetallophosC MG1 MG2 MG3 MG4 Mo-co_dimer N_BRCA1_IG Na_K-ATPase NEAT Neocarzinostat Neurexophilin NPCBM_assoc PapD_C PBP-Tp47_c Peptidase_C25_C Phlebo_G2_C PhoD_N PKD PKD_2 PKD_3 PKD_4 PKD_5 PKD_6 Por_Secre_tail Pox_vIL-18BP Psg1 PTP_tm Pur_ac_phosph_N Qn_am_d_aII Qn_am_d_aIII RabGGT_insert Reeler REJ RET_CLD1 RET_CLD3 RET_CLD4 RGI_lyase RHD_dimer Rho_GDI Rib RibLong SCAB-Ig SKICH SLAM SoxZ SprB SusE SVA SWM_repeat T2SS-T3SS_pil_N Tafi-CsgC TarS_C1 TcA_RBD TcfC TIG TIG_2 TIG_plexin TIG_SUH Tissue_fac Top6b_C Transglut_C Transglut_N TRAP_beta TraQ_transposon UL16 Velvet WIF Wzt_C Y_Y_Y YBD ZirS_C Zona_pellucida



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Curation and family details


Curation View help on the curation process

Seed source: Pseudomonas aeruginosa PA0388, JCSG target SP19004A
Previous IDs: none
Type: Domain
Sequence Ontology: SO:0000417
Author: Godzik A
Number in seed: 40
Number in full: 514
Average length of the domain: 120.30 aa
Average identity of full alignment: 33 %
Average coverage of the sequence by the domain: 81.33 %

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 25.0 25.0
Trusted cut-off 30.8 30.5
Noise cut-off 21.6 20.2
Model length: 121
Family (HMM) version: 8
Download: download the raw HMM for this family

Species distribution

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Colour assignments

Archea Archea Eukaryota Eukaryota
Bacteria Bacteria Other sequences Other sequences
Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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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 DUF4426 domain has been found. There are 4 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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