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14  structures 7  species 1  interaction 921  sequences 7  architectures

Family: SAG (PF04092)

Summary: SRS domain

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This is the Wikipedia entry entitled "SAG1 protein domain". More...

SAG1 protein domain Edit Wikipedia article

Surface Antigen 1 (SAG1)
PDB 1ynt EBI.jpg
Structure of the immunodominant epitope displayed by the Surface Antigen 1 (SAG1) of Toxoplasma gondii complexed to a monoclonal antibody.
Identifiers
Symbol SAG
Pfam PF04092
InterPro IPR007226
SCOP 1kzq
SUPERFAMILY 1kzq

In molecular biology, the SAG1 protein domain is an example of a group of glycosylphosphatidylinositol (GPI)-linked proteins named SRSs (SAG1 related sequence).[1] SAG1 is found on the surface of a protozoan parasite Toxoplasma gondii. This parasite infects almost any warm-blooded vertebrate. The surface of T. gondii is coated with a family of developmentally regulated glycosylphosphatidylinositol (GPI)-linked proteins (SRSs), of which SAG1 is the prototypic member.[2]

Function[edit]

SAG1 and the rest of the SRS protein family mediate cell adhesion to the host cell. They also recognise herapin sulphate proteoglycans, which are part of the Extracellular matrix.[3]

Structure[edit]

The structure of the immunodominant SAG1 antigen reveals a homodimeric configuration.[3] This family of surface antigens is found in other apicomplexans. This particular antigen contains many cysteine residues which lead to disulphide bridge formation.[2]

N-terminal domain[edit]

This domain has a sequence length of at least 130 amino acids which fold to give a beta sheet sandwich.[1]

C terminal domain[edit]

This protein domain contains 120 amino acids.[1]

SRS fold[edit]

There is a fold within this structure which is conserved amongst SRS proteins, and therefore named the SRS fold. The role of this fold is to aid the binding to cells, and promote infection within the host organism. The structure of this fold is analogous to the topology topology of the cupredoxin, azurin, a form of copper binding protein.[1]

References[edit]

  1. ^ a b c d He XL, Grigg ME, Boothroyd JC, Garcia KC (2002). "Structure of the immunodominant surface antigen from the Toxoplasma gondii SRS superfamily.". Nat Struct Biol 9 (8): 606–11. doi:10.1038/nsb819. PMID 12091874. 
  2. ^ a b Cesbron-Delauw MF, Tomavo S, Beauchamps P, Fourmaux MP, Camus D, Capron A et al. (1994). "Similarities between the primary structures of two distinct major surface proteins of Toxoplasma gondii.". J Biol Chem 269 (23): 16217–22. PMID 8206924. 
  3. ^ a b Swirnoff AH, Apel ED, Svaren J, Sevetson BR, Zimonjic DB, Popescu NC, Milbrandt J (January 1998). "Nab1, a corepressor of NGFI-A (Egr-1), contains an active transcriptional repression domain". Mol. Cell. Biol. 18 (1): 512–24. PMC 115883. PMID 9418898. 

This article incorporates text from the public domain Pfam and InterPro IPR007226

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.

SRS domain Provide feedback

Toxoplasma gondii is a persistent protozoan parasite capable of infecting almost any warm-blooded vertebrate. The surface of Toxoplasma is coated with a family of developmentally regulated glycosylphosphatidylinositol (GPI)-linked proteins (SRSs), of which SAG1 is the prototypic member. SRS proteins mediate attachment to host cells and interface with the host immune response to regulate the virulence of the parasite. SAG1 is composed of two disulphide linked SRS domains. These have 6 cysteines that form 1-6,2-5 and 3-4 pairings. The structure of the immunodominant SAG1 antigen reveals a homodimeric configuration [2]. The SRS domain is found in a single copy in the SAG2 proteins. This family of surface antigens are found in other apicomplexans.

Literature references

  1. Cesbron-Delauw MF, Tomavo S, Beauchamps P, Fourmaux MP, Camus D, Capron A, Dubremetz JF; , J Biol Chem 1994;269:16217-16222.: Similarities between the primary structures of two distinct major surface proteins of Toxoplasma gondii. PUBMED:8206924 EPMC:8206924

  2. He XL, Grigg ME, Boothroyd JC, Garcia KC; , Nat Struct Biol 2002;0:0-0.: Structure of the immunodominant surface antigen from the Toxoplasma gondii SRS superfamily. PUBMED:12091874 EPMC:12091874

  3. Lekutis C, Ferguson DJ, Grigg ME, Camps M, Boothroyd JC. , Int J Parasitol 2001;31:1285-1292.: Surface antigens of Toxoplasma gondii: variations on a theme. PUBMED:11566296 EPMC:11566296


External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR007226

Toxoplasma gondii is a persistent protozoan parasite capable of infecting almost any warm-blooded vertebrate. The surface of T. gondii is coated with a family of developmentally regulated glycosylphosphatidylinositol (GPI)-linked proteins (SRSs), of which SAG1 is the prototypic member. SRS proteins mediate attachment to host cells and interface with the host immune response to regulate the virulence of the parasite. The structure of the immunodominant SAG1 antigen reveals a homodimeric configuration [PUBMED:9418898]. This family of surface antigens is found in other apicomplexans.

Gene Ontology

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Domain organisation

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Alignments

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We make a range of alignments for each Pfam-A family. You can see a description of each above. You can view these alignments in various ways but please note that some types of alignment are never generated while others may not be available for all families, most commonly because the alignments are too large to handle.

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(58)
Full
(921)
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(924)
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(325)
RP35
(325)
RP55
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RP75
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  Seed
(58)
Full
(921)
Representative proteomes NCBI
(924)
Meta
(0)
RP15
(325)
RP35
(325)
RP55
(768)
RP75
(768)
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  Seed
(58)
Full
(921)
Representative proteomes NCBI
(924)
Meta
(0)
RP15
(325)
RP35
(325)
RP55
(768)
RP75
(768)
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You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.

External links

MyHits provides a collection of tools to handle multiple sequence alignments. For example, one can refine a seed alignment (sequence addition or removal, re-alignment or manual edition) and then search databases for remote homologs using HMMER3.

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Curation and family details

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Curation View help on the curation process

Seed source: Pfam-B_1675 (release 7.3)
Previous IDs: none
Type: Family
Author: Bateman A
Number in seed: 58
Number in full: 921
Average length of the domain: 131.00 aa
Average identity of full alignment: 20 %
Average coverage of the sequence by the domain: 67.81 %

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 20.8 20.8
Trusted cut-off 20.8 20.8
Noise cut-off 20.6 20.4
Model length: 124
Family (HMM) version: 8
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Species distribution

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Interactions

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SAG

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 SAG domain has been found. There are 14 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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