Summary

BTK motif

Zinc-binding motif containing conserved cysteines and a histidine. Always found C-terminal to PH domains. The crystal structure [1] shows this motif packs against the PH domain. The PH+Btk module pair has been called the Tec homology (TH) region [3].

Literature references

Hyvonen M, Saraste M; , EMBO J 1997;16:3396-3404.: Structure of the PH domain and Btk motif from Bruton's tyrosine kinase: molecular explanations for X-linked agammaglobulinaemia. PUBMED:9218782
Vihinen M, Nore BF, Mattsson PT, Backesjo CM, Nars M, Koutaniemi S, Watanabe C, Lester T, Jones A, Ochs HD, Smith CI; , FEBS Lett 1997;413:205-210.: Missense mutations affecting a conserved cysteine pair in the TH domain of Btk. PUBMED:9280283
Vihinen M, Nilsson L, Smith CI; , FEBS Lett 1994;350:263-265.: Tec homology (TH) adjacent to the PH domain. PUBMED:8070576

InterPro entry IPR001562

The Btk-type zinc finger or Btk motif (BM) is a conserved zinc-binding motif containing conserved cysteines and a histidine that is present in certain eukaryotic signalling proteins. The motif is named after Bruton's tyrosine kinase (Btk), an enzyme which is essential for B cell maturation in humans and mice PUBMED:8070576, PUBMED:15661031. Btk is a member of the Tec family of protein tyrosine kinases (PTK). These kinases contain a conserved Tec homology (TH) domain between the N-terminal pleckstrin homology (PH) domain () and the Src homology 3 (SH3) domain (). The N-terminal of the TH domain is highly conserved and known as the Btf motif, while the C-terminal region of the TH domain contains a proline-rich region (PRR). The Btk motif contains a conserved His and three Cys residues that form a zinc finger (although these differ from known zinc finger topologies), while PRRs are commonly involved in protein-protein interactions, including interactions with G proteins PUBMED:9280283, PUBMED:9796816. The TH domain may be of functional importance in various signalling pathways in different species PUBMED:8070576. A complete TH domain, containing both the Btk and PRR regions, has not been found outside the Tec family; however, the Btk motif on its own does occur in other proteins, usually C-terminal to a PH domain (note that although a Btk motif always occurs C-terminal to a PH domain, not all PH domains are followed by a Btk motif).

The crystal structures of Btk show that the Btk-type zinc finger has a globular core, formed by a long loop which is held together by a zinc ion, and that the Btk motif is packed against the PH domain PUBMED:8070576. The zinc-binding residues are a histidine and three cysteines, which are fully conserved in the Btk motif PUBMED:9218782.

Proteins known to contain a Btk-type zinc finger include:

Mammalian Bruton's tyrosine kinase (Btk), a protein tyrosine kinase involved in modulation of diverse cellular processes. Mutations affecting Btk are the cause of X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency in mice.
Mammalian Tec, Bmx, and Itk proteins, which are tyrosine protein kinases of the Tec subfamily.
Drosophila tyrosine-protein kinase Btk29A, which is required for the development of proper ring canals and of male genitalia and required for adult survival.
Mammalian Ras GTPase-activating proteins (RasGAP), which regulate the activation of inactive GDP-bound Ras by converting GDP to GTP.

Gene Ontology

Biological process

intracellular signaling cascade (GO:0007242)

External database links

PANDIT:	PF00779
SCOP:	1btk
SMART:	BTK
SYSTERS:	BTK

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...

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Alignment:	Seed (26) Full (132) NCBI (276) Metagenomics
Viewer:

Formatting options

Alignment:	Seed (26) Full (132)
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 (26) Full (132) NCBI (276) Metagenomics
Full length sequences	Full-sequences (132)

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:

Alignment kindly provided by SMART

Previous IDs:

none

Type:

Motif

Author:

SMART

Number in seed:

26

Number in full:

132

Average length of the domain:

31.80 aa

Average identity of full alignment:

37 %

Average coverage of the sequence by the domain:

4.40 %

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	21.8	21.8
Trusted cut-off	22.0	21.8
Noise cut-off	21.7	21.7

Model length:

32

Family (HMM) version:

12

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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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 MSD 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 BTK domain has been found.

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Family: BTK (PF00779)

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