The calponin homology domain (also known as CH-domain) is a superfamily of actin-binding domains found in both cytoskeletal proteins and signal transduction proteins [1]. It comprises the following groups of actin-binding domains:

• Actinin-type (including spectrin, fimbrin, ABP-280) (see IPR001589).
• Calponin-type (see IPR000557).

A comprehensive review of proteins containing this type of actin-binding domains is given in [2].

The CH domain is involved in actin binding in some members of the family. However, in calponins there is evidence that the CH domain is not involved in their actin binding activity [3]. Most proteins have two copies of the CH domain, however some proteins such as calponin and the human vav proto-oncogene (P15498) have only a single copy. The structure of an example CH-domain has recently been solved [4].

Proteins containing a calponin domain include:

• Calponin, which is involved in the regulation of contractility and organisation of the actin cytoskeleton in smooth muscle cells [5].
• Beta-spectrin, a major component of a submembrane cytoskeletal network connecting actin filaments to integral plasma membrane proteins [6].
• The actin-cross-linking domain of the fimbrin/plastin family of actin filament bundling or cross-linking proteins [7].
• Utrophin,a close homologue of dystrophin [8].
• Dystrophin, the protein found to be defective in Duchenne muscular dystrophy; this protein contains a tandem repeat of two CH domains [9].
• Actin-binding domain of plectin, a large and widely expressed cytolinker protein [10].
• The N-terminal microtubule-binding domain of microtubule-associated protein eb1 (end-binding protein), a member of a conserved family of proteins that localise to the plus-ends of microtubules [11].
• Ras GTPase-activating-like protein rng2, an IQGAP protein that is essential for the assembly of an actomyosin ring during cytokinesis [12].
• Transgelin, which suppresses androgen receptor transactivation [13].

1. Does Vav bind to F-actin through a CH domain? FEBS Lett. 374, 149-51
2. Actin-binding proteins. 1: Spectrin super family. J. Mol. Biol. 2, 703-800
3. The single CH domain of calponin is neither sufficient nor necessary for F-actin binding. J. Cell. Sci. 111 ( Pt 13), 1813-21
4. Crystal structure of a calponin homology domain. Nat. Struct. Biol. 4, 175-9
5. Solution structure of the calponin CH domain and fitting to the 3D-helical reconstruction of F-actin:calponin. Acta Crystallogr. D Biol. Crystallogr. 10, 249-58
6. beta-Spectrin functions independently of Ankyrin to regulate the establishment and maintenance of axon connections in the Drosophila embryonic CNS. Mol. Endocrinol. 134, 273-84
7. The structure of an actin-crosslinking domain from human fimbrin. Development 4, 708-12
8. The 2.0 A structure of the second calponin homology domain from the actin-binding region of the dystrophin homologue utrophin. Structure 285, 1257-64
9. The structure of the N-terminal actin-binding domain of human dystrophin and how mutations in this domain may cause Duchenne or Becker muscular dystrophy. Structure 8, 481-91
10. Actin-binding domain of mouse plectin. Crystal structure and binding to vimentin. Nat. Struct. Biol. 271, 1873-84
11. Crystal structure of the amino-terminal microtubule-binding domain of end-binding protein 1 (EB1). Eur. J. Biochem. 278, 36430-4
12. Structure, crystal packing and molecular dynamics of the calponin-homology domain of Schizosaccharomyces pombe Rng2. J. Biol. Chem. 60, 1396-403
13. Transgelin functions as a suppressor via inhibition of ARA54-enhanced androgen receptor transactivation and prostate cancer cell growth. null 21, 343-58

The calponin homology domain (also known as CH-domain) is a superfamily of actin-binding domains
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