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58  structures 1893  species 0  interactions 3383  sequences 23  architectures

Family: SQS_PSY (PF00494)

Summary: Squalene/phytoene synthase

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Squalene/phytoene synthase Provide feedback

No Pfam abstract.

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR002060

Squalene synthase EC (farnesyl-diphosphate farnesyltransferase) (SQS) and Phytoene synthase EC (PSY) share a number of functional similarities. These similarities are also reflected at the level of their primary structure [PUBMED:8294001, PUBMED:8474436, PUBMED:8250898]. In particular three well conserved regions are shared by SQS and PSY; they could be involved in substrate binding and/or the catalytic mechanism.

SQS catalyzes the conversion of two molecules of farnesyl diphosphate (FPP) into squalene. It is the first committed step in the cholesterol biosynthetic pathway. The reaction carried out by SQS is catalyzed in two separate steps: the first is a head-to-head condensation of the two molecules of FPP to form presqualene diphosphate; this intermediate is then rearranged in a NADP-dependent reduction, to form squalene: 2 FPP -> presqualene diphosphate + NADP -> squalene SQS is found in eukaryotes. In yeast it is encoded by the ERG9 gene, in mammals by the FDFT1 gene. SQS seems to be membrane-bound.

PSY catalyzes the conversion of two molecules of geranylgeranyl diphosphate (GGPP) into phytoene. It is the second step in the biosynthesis of carotenoids from isopentenyl diphosphate. The reaction carried out by PSY is catalyzed in two separate steps: the first is a head-to-head condensation of the two molecules of GGPP to form prephytoene diphosphate; this intermediate is then rearranged to form phytoene. 2 GGPP -> prephytoene diphosphate -> phytoene PSY is found in all organisms that synthesize carotenoids: plants and photosynthetic bacteria as well as some non- photosynthetic bacteria and fungi. In bacteria PSY is encoded by the gene crtB. In plants PSY is localized in the chloroplast.

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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Alignments

We store a range of different sequence alignments for families. As well as the seed alignment from which the family is built, we provide the full alignment, generated by searching the sequence database using the family HMM. We also generate alignments using four representative proteomes (RP) sets, the NCBI sequence database, and our metagenomics sequence database. More...

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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.

  Seed
(152)
Full
(3383)
Representative proteomes NCBI
(3142)
Meta
(2434)
RP15
(384)
RP35
(788)
RP55
(1058)
RP75
(1260)
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Format an alignment

  Seed
(152)
Full
(3383)
Representative proteomes NCBI
(3142)
Meta
(2434)
RP15
(384)
RP35
(788)
RP55
(1058)
RP75
(1260)
Alignment:
Format:
Order:
Sequence:
Gaps:
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We make all of our alignments available in Stockholm format. You can download them here as raw, plain text files or as gzip-compressed files.

  Seed
(152)
Full
(3383)
Representative proteomes NCBI
(3142)
Meta
(2434)
RP15
(384)
RP35
(788)
RP55
(1058)
RP75
(1260)
Raw Stockholm Download   Download   Download   Download   Download   Download   Download   Download  
Gzipped Download   Download   Download   Download   Download   Download   Download   Download  

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.

Pfam alignments:

HMM logo

HMM logos is one way of visualising profile HMMs. Logos provide a quick overview of the properties of an HMM in a graphical form. You can see a more detailed description of HMM logos and find out how you can interpret them here. More...

Trees

This page displays the phylogenetic tree for this family's seed alignment. We use FastTree to calculate neighbour join trees with a local bootstrap based on 100 resamples (shown next to the tree nodes). FastTree calculates approximately-maximum-likelihood phylogenetic trees from our seed alignment.

Note: You can also download the data file for the tree.

Curation and family details

This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.

Curation View help on the curation process

Seed source: Prosite
Previous IDs: none
Type: Domain
Author: Finn RD
Number in seed: 152
Number in full: 3383
Average length of the domain: 253.00 aa
Average identity of full alignment: 23 %
Average coverage of the sequence by the domain: 78.59 %

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 26.0 26.0
Trusted cut-off 26.0 26.1
Noise cut-off 25.8 25.9
Model length: 267
Family (HMM) version: 14
Download: download the raw HMM for this family

Species distribution

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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 SQS_PSY domain has been found. There are 58 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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