Domain repeats can also allow duplication of active sites or binding sites such as the calcium binding sites in calmodulin or the 9 DNA-binding zinc fingers of the transcription factor TFIIID.
A few examples:
1. an immunoglobulin Fab fragment which contains two ig constant domains and two ig variable domains
2. the two lobes of lactoferrin, each being composed of two similar domains
3. the bi-lobal monomeric aspartic proteinase, pepsin, and the dimeric HIV proteinase which possesses similar activities
4. zinc fingers
back to top
back to roles of protein domains