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8  structures 19  species 3  interactions 44  sequences 1  architecture

Family: Feld-I_B (PF09252)

Summary: Allergen Fel d I-B chain

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Fel d 1 Edit Wikipedia article

Major allergen I polypeptide chain 2
Fel d 1.png
Crystallographic structure of the Fel d 1 dimer, the primary allergen present in cat saliva.[1]
Symbol CH2
Alt. symbols Fel d I, AG4, Allergen Cat-1
Entrez 677879
UniProt P30440
Allergen Fel d I-B chain
PDB 2ejn EBI.jpg
structural characterization of the tetrameric form of the major cat allergen fel d 1
Symbol Feld-I_B
Pfam PF09252
Pfam clan CL0370
InterPro IPR015332
SCOP 1puo

Fel d 1 is a protein that in cats is encoded by the CH1 (chain 1/Fel d 1-A) and CH2 (chain 2/Fel d 1-B) genes.[2][3]

Fel d 1, produced largely in cat saliva and sebaceous glands, is the primary allergen present on cats and kittens.[1] Fel d 1 is also produced by cat skin itself.[4] The protein is of an unknown function to the animal but causes an IgG or IgE reaction in sensitive humans (either as an allergic or asthmatic response). Removal of soft surfaces in the home (carpet, furniture), frequent washings of bed linens, HEPA filters and even washing cats has been proven to reduce the amounts of Fel d 1 present in the home.

Female cats produce a lower level of Fel d 1 than males, and neutered males produce a lower level of Fel d 1 than unneutered males.[5]

Neutered males produce Fel d 1 in levels similar to females (both intact and spayed females produce Fel d 1 in similar levels). Even though females and neutered males produce Fel d 1 in lower levels, they still produce enough to cause allergic symptoms in sensitive individuals.

A variant of Fel-D1 is present in the venom of the slow loris (Primate: Nycticebus). Slow lorises are one of only a few venomous mammals and the only known venomous primate, possessing a dual-composite venom of saliva and brachial gland exudate (BGE) [6]. The BGE possesses a protein resembling Fel-D1, which may effect host species as an allergen as a constitute of the venom, and possess a communicative function.


The complete quaternary structure of Fel d 1 has been determined.[1] The allergen is a tetrameric glycoprotein consisting of two disulfide-linked heterodimers of chains 1 and 2. Fel d 1 chains 1 and 2 share structural similarity with uteroglobin, a secretoglobin superfamily member; chain 2 is a glycoprotein with N-linked oligosaccharides. Both chains share an all alpha-helical structure.[1]

See also


  1. ^ a b c d PDB: 1PUO​; Kaiser L, Grönlund H, Sandalova T, Ljunggren HG, van Hage-Hamsten M, Achour A, Schneider G (September 2003). "The crystal structure of the major cat allergen Fel d 1, a member of the secretoglobin family". J. Biol. Chem. 278 (39): 37730–5. doi:10.1074/jbc.M304740200. PMID 12851385. 
  2. ^ Morgenstern JP, Griffith IJ, Brauer AW, Rogers BL, Bond JF, Chapman MD, Kuo MC (November 1991). "Amino acid sequence of Fel dI, the major allergen of the domestic cat: protein sequence analysis and cDNA cloning". Proc. Natl. Acad. Sci. U.S.A. 88 (21): 9690–4. doi:10.1073/pnas.88.21.9690. PMC 52784Freely accessible. PMID 1946388. 
  3. ^ Griffith IJ, Craig S, Pollock J, Yu XB, Morgenstern JP, Rogers BL (April 1992). "Expression and genomic structure of the genes encoding FdI, the major allergen from the domestic cat". Gene. 113 (2): 263–8. doi:10.1016/0378-1119(92)90405-E. PMID 1572548. 
  4. ^ DABROWSKI, A; VANDERBREMPT, X; SOLER, M; SEGURET, N; LUCCIANI, P; CHARPIN, D; VERVLOET, D. "Cat skin as an important source of Fel d I allergen". Journal of Allergy and Clinical Immunology. 86 (4): 462–465. doi:10.1016/S0091-6749(05)80200-3. 
  5. ^ Sex difference in Fel d 1 allergen production. . Accessed 31 Oct 2016.
  6. ^ Nekaris, K. Anne-Isola; Moore, Richard S.; Rode, E. Johanna; Fry, Bryan G. (2013-09-27). "Mad, bad and dangerous to know: the biochemistry, ecology and evolution of slow loris venom". Journal of Venomous Animals and Toxins including Tropical Diseases. 19: 21. doi:10.1186/1678-9199-19-21. ISSN 1678-9199. 

This article incorporates text from the public domain Pfam and InterPro IPR015332

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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.

Allergen Fel d I-B chain Provide feedback

Members of this family of cat allergens adopt a helical structure consisting of eight alpha helices, in a Uteroglobin-like fold. They are one of the most important causes of allergic asthma worldwide [1].

Literature references

  1. Kaiser L, Gronlund H, Sandalova T, Ljunggren HG, van Hage-Hamsten M, Achour A, Schneider G; , J Biol Chem. 2003;278:37730-37735.: The crystal structure of the major cat allergen Fel d 1, a member of the secretoglobin family. PUBMED:12851385 EPMC:12851385

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External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR015332

Allergies are hypersensitivity reactions of the immune system to specific substances called allergens (such as pollen, stings, drugs, or food) that, in most people, result in no symptoms. A nomenclature system has been established for antigens (allergens) that cause IgE-mediated atopic allergies in humans. The nomenclature system uses the first three letters of the genus, followed by the first letter of the species name, followed by a number (additional letters can be added to the name as required to discriminate between similar designations).

Fel d 1 is allergen 1 from Felis silvestris catus (Cat), which is an important agent in human allergic reactions [PUBMED:17543334]. The protein is expressed in saliva and sebaceous glands. The complete primary structure of Fel d 1 has been determined [PUBMED:12851385]. The allergen is tetrameric glycoprotein consisting of two disulphide-linked heterodimers of chains 1 and 2, which have been shown to be encoded by different genes. Fel d 1 chains 1 and 2 share structural similarity with uteroglobin, a secretoglobin superfamily member; chain 2 is a glycoprotein with N-linked oligosaccharides.

This entry represents Fel d 1 chain 2.

Gene Ontology

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Domain organisation

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Pfam Clan

This family is a member of clan Uteroglobin (CL0370), which has the following description:

Members of this superfamily are disulfide-linked dimers of two identical chains, with 4 helices in each. They constitute important new cat, rat and rabbit allergens that are contributing to asthma world-wide.

The clan contains the following 2 members:

Feld-I_B Uteroglobin


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Seed source: pdb_1puo
Previous IDs: none
Type: Domain
Sequence Ontology: SO:0000417
Author: Sammut SJ
Number in seed: 15
Number in full: 44
Average length of the domain: 65.00 aa
Average identity of full alignment: 41 %
Average coverage of the sequence by the domain: 59.77 %

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HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 45638612 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 24.0 24.0
Trusted cut-off 25.6 25.3
Noise cut-off 23.2 22.8
Model length: 67
Family (HMM) version: 10
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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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There are 3 interactions for this family. More...

Uteroglobin Uteroglobin Feld-I_B


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 Feld-I_B domain has been found. There are 8 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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