Helix-Loop-Helix Domain

Definition 1

In transcription regulators of cell cycle control, cell determination, and cell differentiation, the conserved HLH (Helix-Loop-Helix) Domain of 40-50 amino acids forms amphipathic helixes between a variable loop. HLHs typically mediate homo- or heterodimerization through interactions with self or other motifs to activate or inactivate trans-activating function. The N-helix often contains DNA-interacting basic residues; the C-helix typically contains characteristically spaced hydrophobic residues. An adjacent basic region of 15 amino acids in most HLH proteins binds to DNA. Basic (b)HLH proteins bind variants of the 'CANNTG' E-box. Proteins lacking the basic domain act as inhibitors, failing to bind DNA. bHLH proteins exhibit specific dimerization partner combinations. In calcium-binding proteins, certain invariant hydrophilic loop residues in the HLH motif bind calcium. (NCI Thesaurus)

Definition 2

Recurring supersecondary structures characterized by 20 amino acids folding into two alpha helices connected by a non-helical "loop" segment. They are found in many sequence-specific DNA-BINDING PROTEINS and in CALCIUM-BINDING PROTEINS. (NLM, Medical Subject Headings)

YOU MAY ALSO LIKE

Helix

A twisted curved structure such as a coil spring or corkscrew.

Helium

A gaseous element with atomic symbol He, atomic number 2, and atomic weight 4.00.

Heliotropium arborescens

A plant whose roots are used as a sedative and to treat certain medical conditions. It is being studied as a way…

Helifix Coil Device Component

A coil designed to allow a Helifix pacing electrode to be placed in the endocardium.

Helicotrema

An opening in the cochlea where the scala tympani and scala vestibuli join to communicate.

Helicobacteraceae

A taxonomic family of bacterium in the phylum Proteobacteria that includes the genera Helicobacter, Flexispira and Wolinella, among others.