Summary: Rhomboid family
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Rhomboid protease Edit Wikipedia article
The rhomboid proteases are a family of enzymes that exist in almost all species. They are proteases: they cut the polypeptide chain of other proteins. This proteolytic cleavage is irreversible in cells, and an important type of cellular regulation. Although proteases are one of the earliest and best studied class of enzyme, rhomboids belong to a much more recently discovered type: the intramembrane proteases. What is unique about intramembrane proteases is that their active sites are buried in the lipid bilayer of cell membranes, and they cleave other transmembrane proteins within their transmembrane domains. About 30% of all proteins have transmembrane domains, and their regulated processing often has major biological consequences. Accordingly, rhomboids regulate many important cellular processes, and may be involved in a wide range of human diseases.
Rhomboids are intramembrane serine proteases. The other types of intramembrane protease are aspartyl- and metallo-proteases, respectively. The presenilins and signal peptide peptidase-like family, which are intramembrane aspartyl proteases, cleave substrates that include the Notch receptor and the amyloid precursor protein, which is implicated in Alzheimer's disease. The site-2 protease family, which are intramembrane metalloproteases, regulate among other things cholesterol biosynthesis and stress responses in bacteria. The different intramembrane protease families are evolutionarily and mechanistically unrelated, but there are clear common functional themes that link them. Rhomboids are perhaps the best characterised class.
History of rhomboid discovery
Rhomboids were first named after a mutation in the fruit fly Drosophila, discovered in a famous genetic screen that led to a Nobel Prize for Christiane Nüsslein-Volhard and Eric Wieschaus. In that screen they found a number of mutants with similar phenotypes: ‘pointy’ embryonic head skeletons. They named them each with a pointy-themed name – one was rhomboid. Genetic analysis later proved that this group of genes were members of the epidermal growth factor (EGF) receptor signalling pathway, and that rhomboid was needed to generate the signal that activates the EGF receptor. The molecular function of rhomboid took a bit longer to unravel but a combination of genetics and molecular techniques led to the discovery that Drosophila rhomboid and other members of the family were the first known intramembrane serine proteases.
Biological role of rhomboids
Rhomboids were first discovered as proteases that regulate EGF receptor signalling in Drosophila. By releasing the extracellular domain of the growth factor Spitz, from its transmembrane precursor, rhomboid triggers signalling. Since then, many other important biological functions have been proposed.
- Although less well established than in Drosophila, there is some evidence that rhomboids may participate in growth factor signalling in mammals, including humans. They have also been implicated in ephrin signalling, the cleavage of the anticoagulant protein thrombomodulin  and wound healing.
- All eukaryotes have a mitochondrial rhomboid. In yeast this has been shown to control mitochondrial function and morphology by regulating membrane fusion via the cleavage of a dynamin-like GTPase called Mgm1p, the orthologue of human OPA1. In Drosophila, the mitochondrial rhomboid also regulates mitochondrial membrane fusion. In mammals too, mitochondrial function is disrupted in mutants of PARL, the mitochondrial rhomboid, but the range of functions is more complex. PARL regulates the remodelling of mitochondrial cristae, is implicated in cell death  and metabolism, and there is increasing evidence of an important role in Parkinson's Disease;
- Apicomplexan parasites like Plasmodium (the agent that causes malaria) and Toxoplasma appear to use rhomboids to cleave cell surface proteins that participate in the host invasion process. Rhomboids have also been implicated in the pathogenicity of other parasites.
- A rhomboid in the Gram-negative bacterium Providencia stuartii is required for the function of the twin-arginine protein translocation (TAT) machinery.
Structure and enzyme function of rhomboids
Rhomboids were the first intramembrane proteases for which a high resolution crystal structure was solved. These structures confirmed predictions that rhomboids have a core of six transmembrane domains, and that the catalytic site depends on a serine and histidine catalytic dyad. The structures also explained how a proteolytic reaction, which requires water molecules, can occur in the hydrophobic environment of a lipid bilayer: one of the central mysteries of intramembrane proteases. The active site of rhomboid protease is in a hydrophilic indentation, in principle accessible to water from the bulk solution. However, it has been proposed that there might be an auxiliary mechanism to facilitate access of water molecules to the catalytic dyad at the bottom of the active site to ensure catalytic efficiency.
The active site of rhomboid protease is protected laterally from the lipid bilayer by its six constituent transmembrane helices, suggesting that substrate access to rhomboid active site is regulated. One area of uncertainty has been the route of substrate access. Substrates were initially proposed to enter between transmembrane segments (TMSs) 1 and 3, but current evidence strongly supports an alternative access point, between TMSs 2 and 5. This notion is also supported by the fact that mutations in TMS 5 have only a marginal effect on the thermodynamic stability of rhomboid, unlike other regions of the molecule. Very recently, the first ever co-crystal structure of an intramembrane protease - the Escherichia coli rhomboid protease GlpG - and a substrate-derived peptide bound in the active site  confirms and extends this substrate access model and provides implications for the mechanism of other rhomboid-superfamily proteins. The details of how a substrate TMS may be recognized by rhomboid are however still unclear. Some authors propose that substrate access involves a large lateral displacement movement of TMS 5 to open up the core of rhomboid. Other reports instead suggest that large lateral movement of TMS 5 is not required, and propose that the surface of TMSs 2 and 5 rather serves as an "intramembrane exosite" mediating the recognition of substrate TMS.
Rhomboids do not cleave all transmembrane domains. In fact, they are highly specific, with a limited number of substrates. Most natural Rhomboid substrates known so far are type 1 single transmembrane domain proteins, with their amino termini in the luminal/extracellular compartment. However, recent studies suggested that type 2 membrane protein (i.e. with opposite topology: the amino terminus is cytoplasmic), or even multipass membrane proteins could act as rhomboid substrates. The specificity of rhomboids underlies their ability to control functions in a wide range of biological processes and, in turn, understanding what makes a particular transmembrane domain into a rhomboid substrate can shed light on rhomboid function in different contexts.
Initial work indicated that rhomboids recognise instability of the transmembrane alpha-helix at the site of cleavage as the main substrate determinant. More recently, it has been found that rhomboid substrates are defined by two separable elements: the transmembrane domain and a primary sequence motif in or immediately adjacent to it. This recognition motif directs where the substrate is cleaved, which can occur either within, or just outside, the transmembrane domain, in the juxtamembrane region. In the former case helix destabilising residues downstream in substrate TMS are also necessary for efficient cleavage. A detailed enzyme kinetics analysis has in fact shown that the recognition motif interactions with rhomboid active site determine the kcat of substrate cleavage. The principles of substrate TMS recognition by rhomboid remain poorly understood, but numerous lines of evidence indicate that rhomboids (and perhaps also other intramembrane proteases) somehow recognise the structural flexibility or dynamics of transmembrane domain of their substrates. Full appreciation of the biophysical and structural principles involved will require structural characterisation of the complex of rhomboid with the full transmembrane substrate. As a first step towards this goal, a recent co-crystal structure of the enzyme in complex with a substrate-derived peptide containing mechanism-based inhibitor explains the observed recognition motif sequence preferences in rhomboid substrates structurally, and provides a significant advance in the current understanding of rhomboid specificity and mechanism of rhomboid-family proteins.
In some Gram-negative bacteria, including Shewanella and Vibrio, up to thirteen proteins are found with GlyGly-CTERM, a C-terminal homology domain consisting of a glycine-rich motif, a highly hydrophobic transmembrane helix, and a cluster of basic residues. This domain appears to be the recognition sequence for rhombosortase, a branch of the rhomboid protease family limited to just those bacteria with the GlyGly-CTERM domain.
Medical significance of rhomboids
The diversity of biological functions already known to depend on rhomboids is reflected in evidence that rhomboids play a role in a variety if diseases including cancer, parasite infection, and diabetes. It is important to note, however, that there is no case yet established where a precise medical significance is fully validated.
No drugs that modulate rhomboid activity have yet been reported, although a recent study has identified small molecule, mechanism-based inhibitors that could provide a basis for future drug development.
The rhomboid-like family
Rhomboid proteases appear to be conserved in all eukaryotes and the vast majority of prokaryotes. Bioinformatic analysis highlights that some members of the rhomboid family lack the amino acid residues essential for proteolysis, implying that they cannot cleave substrates. These ‘pseudoproteases’ include a subfamily that have been named the iRhoms  (also known as RHBDF1 and RHBDF2). iRhoms can promote the ER associated degradation (ERAD) of EGF receptor ligands in Drosophila, thus providing a mechanism for regulating EGF receptor activity in the brain. This implies that the fundamental cellular quality control mechanism is exploited by multicellular organisms to regulate signalling between cells. Interestingly, in the mouse, iRhoms are key trafficking chaperones required for the ER export of ADAM17/TACE and its maturation. iRhoms are thus required for the TNF-alpha and EGF receptor signalling, making them medically highly attractive.
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- Urban, S.; Lee, J. R.; Freeman, M. (2001-10-19). "Drosophila rhomboid-1 defines a family of putative intramembrane serine proteases". Cell. 107 (2): 173–182. ISSN 0092-8674. PMID 11672525.
- Lemberg, Marius K.; Menendez, Javier; Misik, Angelika; Garcia, Maite; Koth, Christopher M.; Freeman, Matthew (2005-02-09). "Mechanism of intramembrane proteolysis investigated with purified rhomboid proteases". The EMBO journal. 24 (3): 464–472. doi:10.1038/sj.emboj.7600537. ISSN 0261-4189. PMC . PMID 15616571.
- Urban, Sinisa; Wolfe, Michael S. (2005-02-08). "Reconstitution of intramembrane proteolysis in vitro reveals that pure rhomboid is sufficient for catalysis and specificity". Proceedings of the National Academy of Sciences of the United States of America. 102 (6): 1883–1888. doi:10.1073/pnas.0408306102. ISSN 0027-8424. PMC . PMID 15684070.
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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.
Rhomboid family Provide feedback
This family contains integral membrane proteins that are related to Drosophila rhomboid protein P20350. Members of this family are found in bacteria and eukaryotes. Rhomboid promotes the cleavage of the membrane-anchored TGF-alpha-like growth factor Spitz, allowing it to activate the Drosophila EGF receptor. Analysis has shown that Rhomboid-1 is an intramembrane serine protease  ( EC:184.108.40.206). Parasite-encoded rhomboid enzymes are also important for invasion of host cells by Toxoplasma and the malaria parasite .
Bier E, Jan LY, Jan YN; , Genes Dev 1990;4:190-203.: rhomboid, a gene required for dorsoventral axis establishment and peripheral nervous system development in Drosophila melanogaster. PUBMED:2110920 EPMC:2110920
Koonin EV, Makarova KS, Rogozin IB, Davidovic L, Letellier MC, Pellegrini L; , Genome Biol 2003;4:R19.: The rhomboids: a nearly ubiquitous family of intramembrane serine proteases that probably evolved by multiple ancient horizontal gene transfers. PUBMED:12620104 EPMC:12620104
Urban S, Wolfe MS; , Proc Natl Acad Sci U S A. 2005;102:1883-1888.: Reconstitution of intramembrane proteolysis in vitro reveals that pure rhomboid is sufficient for catalysis and specificity. PUBMED:15684070 EPMC:15684070
Brossier F, Jewett TJ, Sibley LD, Urban S; , Proc Natl Acad Sci U S A. 2005;102:4146-4151.: A spatially localized rhomboid protease cleaves cell surface adhesins essential for invasion by Toxoplasma. PUBMED:15753289 EPMC:15753289
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR022764This entry represents a six transmembrane helix rhomboid domain.
This domain is found in serine peptidases belonging to the MEROPS peptidase family S54 (Rhomboid, clan ST). They are integral membrane proteins related to the Drosophila melanogaster (Fruit fly) rhomboid protein SWISSPROT. Members of this family are found in archaea, bacteria and eukaryotes.
The D. melanogaster rhomboid protease cleaves type-1 transmembrane domains using a catalytic triad composed of serine, histidine and asparagine contributed by different transmembrane domains. It cleaves the transmembrane proteins Spitz, Gurken and Keren within their transmembrane domains to release a soluble TGFalpha-like growth factor. Cleavage occurs in the Golgi, following translocation of the substrates from the endoplasmic reticulum membrane by Star, another transmembrane protein. The growth factors are then able to activate the epidermal growth factor receptor [PUBMED:2110920, PUBMED:11672525].
Few substrates of mammalian rhomboid homologues have been determined, but rhomboid-like protein 2 has been shown to cleave ephrin B3 [PUBMED:15047175]. Parasite-encoded rhomboid enzymes are also important for invasion of host cells by Toxoplasma and the malaria parasite.
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Cellular component||integral component of membrane (GO:0016021)|
|Molecular function||serine-type endopeptidase activity (GO:0004252)|
Below is a listing of the unique domain organisations or architectures in which this domain is found. More...
The graphic that is shown by default represents the longest sequence with a given architecture. Each row contains the following information:
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This example describes an architecture with one
Gladomain, followed by two consecutive
EGFdomains, and finally a single
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This clan contains proteins from both bacteria and eukaryotes. The Rhomboid protein is an intramembrane serine protease which is involved in epidermal growth factor (EGF)-dependent signalling pathways . The DER1 family is involved in degradation of misfolded ER proteins .
The clan contains the following 3 members:DER1 DUF1751 Rhomboid
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 (reference proteomes) using the family HMM. We also generate alignments using four representative proteomes (RP) sets, the UniProtKB sequence database, 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:
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- alignment generated by searching the metagenomics sequence database using the family HMM
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1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
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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.
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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.
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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.
|Seed source:||Pfam-B_1399 (release 4.1)|
|Author:||Sohrmann M, Bateman A|
|Number in seed:||62|
|Number in full:||7182|
|Average length of the domain:||148.50 aa|
|Average identity of full alignment:||22 %|
|Average coverage of the sequence by the domain:||44.99 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 17690987 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||20|
|Download:||download the raw HMM for this family|
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This visualisation provides a simple graphical representation of the distribution of this family across species. You can find the original interactive tree in the More....
This chart is a modified "sunburst" visualisation of the species tree for this family. It shows each node in the tree as a separate arc, arranged radially with the superkingdoms at the centre and the species arrayed around the outermost ring.
How the sunburst is generated
The tree is built by considering the taxonomic lineage of each sequence that has a match to this family. For each node in the resulting tree, we draw an arc in the sunburst. The radius of the arc, its distance from the root node at the centre of the sunburst, shows the taxonomic level ("superkingdom", "kingdom", etc). The length of the arc represents either the number of sequences represented at a given level, or the number of species that are found beneath the node in the tree. The weighting scheme can be changed using the sunburst controls.
In order to reduce the complexity of the representation, we reduce the number of taxonomic levels that we show. We consider only the following eight major taxonomic levels:
Colouring and labels
Segments of the tree are coloured approximately according to their superkingdom. For example, archeal branches are coloured with shades of orange, eukaryotes in shades of purple, etc. The colour assignments are shown under the sunburst controls. Where space allows, the name of the taxonomic level will be written on the arc itself.
As you move your mouse across the sunburst, the current node will be highlighted. In the top section of the controls panel we show a summary of the lineage of the currently highlighed node. If you pause over an arc, a tooltip will be shown, giving the name of the taxonomic level in the title and a summary of the number of sequences and species below that node in the tree.
Anomalies in the taxonomy tree
There are some situations that the sunburst tree cannot easily handle and for which we have work-arounds in place.
Missing taxonomic levels
Some species in the taxonomic tree may not have one or more of the main eight levels that we display. For example, Bos taurus is not assigned an order in the NCBI taxonomic tree. In such cases we mark the omitted level with, for example, "No order", in both the tooltip and the lineage summary.
Unmapped species names
The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.
So that these nodes are not simply omitted from the sunburst tree, we group them together in a separate branch (or segment of the sunburst tree). Since we cannot determine the lineage for these unmapped species, we show all levels between the superkingdom and the species as "uncategorised".
Since we reduce the species tree to only the eight main taxonomic levels, sequences that are mapped to the sub-species level in the tree would not normally be shown. Rather than leave out these species, we map them instead to their parent species. So, for example, for sequences belonging to one of the Vibrio cholerae sub-species in the NCBI taxonomy, we show them instead as belonging to the species Vibrio cholerae.
Too many species/sequences
For large species trees, you may see blank regions in the outer layers of the sunburst. These occur when there are large numbers of arcs to be drawn in a small space. If an arc is less than approximately one pixel wide, it will not be drawn and the space will be left blank. You may still be able to get some information about the species in that region by moving your mouse across the area, but since each arc will be very small, it will be difficult to accurately locate a particular species.
The tree shows the occurrence of this domain across different species. More...
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.
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
Please note: for large trees this can take some time. While the tree is loading, you can safely switch away from this tab but if you browse away from the family page entirely, the tree will not be loaded.
There are 3 interactions for this family. More...
We determine these interactions using iPfam, which considers the interactions between residues in three-dimensional protein structures and maps those interactions back to Pfam families. You can find more information about the iPfam algorithm in the journal article that accompanies the website.
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 Rhomboid domain has been found. There are 31 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.
Loading structure mapping...