Excalibur

Excalibur calcium-binding domain

• SMART accession number: SM00894
• Description: Extracellular Ca2+-dependent nuclease YokF from Bacillus subtilis and several other surface-exposed proteins from diverse bacteria are encoded in the genomes in two paralogous forms that differ by a ~45 amino acid fragment, which comprises a novel conserved domain. Sequence analysis of this domain revealed a conserved DxDxDGxxCE motif, which is strikingly similar to the Ca2+-binding loop of the calmodulin-like EF-hand domains, suggesting an evolutionary relationship between them. Functions of many of the other proteins in which the novel domain, named Excalibur (extracellular calcium-binding region), is found, as well as a structural model of its conserved motif are consistent with the notion that the Excalibur domain binds calcium. This domain is but one more example of the diversity of structural contexts surrounding the EF-hand-like calcium-binding loop in bacteria. This loop is thus more widespread than hitherto recognised and the evolution of EF-hand-like domains is probably more complex than previously appreciated.
• Interpro abstract (IPR008613):

  Extracellular Ca ²⁺ -dependent nuclease YokF from Bacillus subtilis and several other surface-exposed proteins from diverse bacteria are encoded in the genomes in two paralogous forms that differ by a ~45 amino acid fragment, which comprises a novel conserved domain. Sequence analysis of this domain revealed a conserved DxDxDGxxCE motif, which is strikingly similar to the Ca ²⁺ -binding loop of the calmodulin-like EF-hand domains, suggesting an evolutionary relationship between them. Functions of many of the other proteins in which the novel domain, named Excalibur (extracellular calcium-binding region), is found, as well as a structural model of its conserved motif are consistent with the notion that the Excalibur domain binds calcium. This domain is but one more example of the diversity of structural contexts surrounding the EF-hand-like calcium-binding loop in bacteria. This loop is thus more widespread than hitherto recognised and the evolution of EF-hand-like domains is probably more complex than previously appreciated [ (PUBMED:12694917) ].

There are 7075 Excalibur domains in 6914 proteins in SMART's nrdb database.

Cellular role (predicted cellular role)

Cellular role: interaction

Literature (relevant references for this domain)

Primary literature is listed below; Automatically-derived, secondary literature is also avaliable.

• Rigden DJ, Jedrzejas MJ, Galperin MY
• An extracellular calcium-binding domain in bacteria with a distantrelationship to EF-hands.
• FEMS Microbiol Lett. 2003; 221: 103-10

Extracellular Ca(2+)-dependent nuclease YokF from Bacillus subtilis andseveral other surface-exposed proteins from diverse bacteria are encodedin the genomes in two paralogous forms that differ by a approximately 45amino acid fragment, which comprises a novel conserved domain. Sequenceanalysis of this domain revealed a conserved DxDxDGxxCE motif, which isstrikingly similar to the Ca(2+)-binding loop of the calmodulin-likeEF-hand domains, suggesting an evolutionary relationship between them.Functions of many of the other proteins in which the novel domain, namedExcalibur (extracellular calcium-binding region), is found, as well as astructural model of its conserved motif are consistent with the notionthat the Excalibur domain binds calcium. This domain is but one moreexample of the diversity of structural contexts surrounding theEF-hand-like calcium-binding loop in bacteria. This loop is thus morewidespread than hitherto recognized and the evolution of EF-hand-likedomains is probably more complex than previously appreciated.

Links (links to other resources describing this domain)

• PFAM: Excalibur
• INTERPRO: IPR008613