Summary

Protein export membrane protein

This family consists of various prokaryotic SecD and SecF protein export membrane proteins. This SecD and SecF proteins are part of the multimeric protein export complex comprising SecA, D, E, F, G, Y, and YajC [1]. SecD and SecF are required to maintain a proton motive force [2].

Literature references

Bolhuis A, Broekhuizen CP, Sorokin A, van Roosmalen ML, Venema G, Bron S, Quax WJ, van Dijl JM; , J Biol Chem 1998;273:21217-21224.: SecDF of Bacillus subtilis, a molecular Siamese twin required for the efficient secretion of proteins. PUBMED:9694879
Arkowitz RA, Wickner W; , EMBO J 1994;13:954-963.: SecD and SecF are required for the proton electrochemical gradient stimulation of preprotein translocation. PUBMED:8112309

InterPro entry IPR003335

Secretion across the inner membrane in some Gram-negative bacteria occurs via the preprotein translocase pathway. Proteins are produced in the cytoplasm as precursors, and require a chaperone subunit to direct them to the translocase component PUBMED:2202721. From there, the mature proteins are either targeted to the outer membrane, or remain as periplasmic proteins. The translocase protein subunits are encoded on the bacterial chromosome.

The translocase itself comprises 7 proteins, including a chaperone protein (SecB), an ATPase (SecA), an integral membrane complex (SecCY, SecE and SecG), and two additional membrane proteins that promote the release of the mature peptide into the periplasm (SecD and SecF) PUBMED:2202721. The chaperone protein SecB PUBMED:11336818 is a highly acidic homotetrameric protein that exists as a "dimer of dimers" in the bacterial cytoplasm. SecB maintains preproteins in an unfolded state after translation, and targets these to the peripheral membrane protein ATPase SecA for secretion PUBMED:10418149. Together with SecY and SecG, SecE forms a multimeric channel through which preproteins are translocated, using both proton motive forces and ATP-driven secretion. The latter is mediated by SecA. The structure of the Escherichia coli SecYEG assembly revealed a sandwich of two membranes interacting through the extensive cytoplasmic domains PUBMED:12167867. Each membrane is composed of dimers of SecYEG. The monomeric complex contains 15 transmembrane helices.

This family consists of various prokaryotic SecD and SecF protein export membrane proteins. The SecD and SecF equivalents of the Gram-positive bacterium Bacillus subtilis are jointly present in one polypeptide, denoted SecDF, that is required to maintain a high capacity for protein secretion. Unlike the SecD subunit of the pre-protein translocase of E. coli, SecDF of B. subtilis was not required for the release of a mature secretory protein from the membrane, indicating that SecDF is involved in earlier translocation steps PUBMED:9694879. Comparison with SecD and SecF proteins from other organisms revealed the presence of 10 conserved regions in SecDF, some of which appear to be important for SecDF function. Interestingly, the SecDF protein of B. subtilis has 12 putative transmembrane domains. Thus, SecDF does not only show sequence similarity but also structural similarity to secondary solute transporters PUBMED:9694879.

Clan

This family is a member of clan RND_permease (CL0322), which contains the following 6 members:

ACR_tran GerA MMPL Patched SecD_SecF Sterol-sensing

Gene Ontology

Cellular component	type II protein secretion system complex (GO:0015627)
Molecular function	protein transporter activity (GO:0008565)
Biological process	protein secretion by the type II secretion system (GO:0015628)

External database links

PANDIT:	PF02355
SYSTERS:	SecD_SecF
Transporter classification:	3.A.5

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

There are various ways to view or download the sequence alignments that we store. You can use a sequence viewer to look at either the seed or full alignment for the family, or you can look at a plain text version of the sequence in a variety of different formats. More...

View options

Alignment:	Seed (19) Full (2916) NCBI (9837) Metagenomics (6135)
Viewer:

Formatting options

Alignment:	Seed (19) Full (2916)
Format:
Order:	Tree Alphabetical
Sequence:	Inserts lower case All upper case
Gaps:
Download/view:	Download View

Download options

Very large alignments can often cause problems for the formatting tool above. If you find that downloading or viewing a large alignment is problematic, you can also download a gzip-compressed, Stockholm-format file containing the seed or full alignment for this family.

You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.

The main seed and full alignments are generated using sequences from the UniProt sequence database. However, we also generate alignments using sequences from the NCBI sequence database and the "metaseq" metagenomics dataset.

You can view alignments from these two additional datasets using the form above, or you can download alignments of NCBI or metagenomics sequences, as gzip-compressed files.

Pfam alignments:	Seed (19) Full (2916) NCBI (9837) Metagenomics (6135)
Full length sequences	Full-sequences (2916)

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 HMMER2.

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. 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 or full alignments.

Note: You can also download the data files for the seed, full, NCBI or metagenomics trees.

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

Seed source:

Pfam-B_844 (release 5.2)

Previous IDs:

none

Type:

Family

Author:

Bashton M, Bateman A

Number in seed:

19

Number in full:

2916

Average length of the domain:

184.50 aa

Average identity of full alignment:

29 %

Average coverage of the sequence by the domain:

34.17 %

HMM information

HMM build commands:

build method: hmmbuild -o /dev/null HMM SEED

search method: hmmsearch -Z 9421015 -E 1000 HMM pfamseq

Model details:

Parameter	Sequence	Domain
Gathering cut-off	20.5	20.5
Trusted cut-off	20.5	20.5
Noise cut-off	20.4	20.4

Model length:

189

Family (HMM) version:

9

Download:

download the raw HMM for this family

Species distribution

Tree controls

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The tree shows the occurrence of this domain across different species. More...

Species trees

We show the species tree in one of two ways. For smaller trees we try to show an interactive representation, which allows you to select specific nodes in the tree and view them as an alignment or as a set of Pfam domain graphics.

Unfortunately we have found that there are problems viewing the interactive tree when the it becomes larger than a certain limit. Furthermore, we have found that Internet Explorer can become unresponsive when viewing some trees, regardless of their size. We therefore show a text representation of the species tree when the size is above a certain limit or if you are using Internet Explorer to view the site.

If you are using IE you can still load the interactive tree by clicking the "Generate interactive tree" button, but please be aware of the potential problems that the interactive species tree can cause.

Interactive tree

For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.

We also count the number of unique sequences on which each domain is found, which is shown in green. Note that a domain may appear multiple times on the same sequence, leading to the difference between these two numbers.

Finally, we group sequences from the same organism according to the NCBI code that is assigned by UniProt, allowing us to count the number of distinct sequences on which the domain is found. This value is shown in the pink boxes.

We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.

You can use the tree controls to manipulate how the interactive tree is displayed:

show/hide the summary boxes
highlight species that are represented in the seed alignment
expand/collapse the tree or expand it to a given depth
select a sub-tree or a set of species within the tree and view them graphically or as an alignment
save a plain text representation of the tree

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Family: SecD_SecF (PF02355)

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