HOMEODOMAIN family

General information

Homeodomain is a DNA-binding domain presented in a number of eukariotic transcription factors that are resposible for regulation of key developmental processes. Homeodomains contain three alpha-helixes forming helix-turn-helix (HTH) topology and a flexible, enriched with basic amino acids N-terminal "hand" (residues 1–9), which changes its conformation during DNA binding. The third alpha-helix is responsible for contact with the major groove of the DNA.

Homeodomain obtaines its name because it is encoded by a highly conserved 180-nucleotides sequence called homeobox, which was firstly discovered in homeotic genes of Drosophila. Later homeoboxes were found in many other genes of various species of eukaryotes. Though they were not found in prokaryotic genomes.

Homeodomains are widely presented in eukaryote proteins. Many of the homeoproteins have been shown to be transcriptional factors, implicating regulation of gene expression, during a variety of important biological processes. They act as activators or repressors of transcription. Homeoproteins can also perform complex functions, for example, they can be both activator and repressor factor of transcription by forming multicomponental complexes with other transcriptional factors. Such complexes gain in high specific binding and affinity to DNA. Homeodomains have higly conserved residues in the third helix: tryptophan in the position 48, asparagine in the position 51 and arginine in the position 53. Homeodomains have conserved primary, secondary and tertuary structure so it can be concluded that they have a single principle and mechanism of recognition of DNA sequence.

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