Basic helix-loop-helix transcription factors

Basic helix-loop-helix transcription factors (bHLH) are a group of transcription factors that play crucial roles in the regulation of gene expression in various biological processes. They are characterized by a specific protein structure known as the basic helix-loop-helix (bHLH) domain.

Structure

The bHLH domain consists of approximately 60 amino acids and is divided into two functionally distinct regions. The basic region is responsible for DNA binding, while the helix-loop-helix region facilitates protein-protein interactions. The basic region contains positively charged amino acids that interact with the negatively charged phosphate backbone of DNA. The helix-loop-helix region consists of two alpha helices separated by a loop of variable length.

Function

bHLH transcription factors bind to specific DNA sequences, known as E-boxes, to regulate gene expression. They can function as homodimers or heterodimers, which allows for a high degree of specificity in target gene regulation. bHLH transcription factors are involved in a wide range of biological processes, including cell cycle regulation, neuronal differentiation, and muscle development.

Classification

bHLH transcription factors can be classified into six groups (A-F) based on their structural characteristics and functional roles. Group A includes general bHLH proteins that are expressed in many cell types, while groups B-F contain tissue-specific bHLH proteins.

Clinical significance

Mutations in bHLH transcription factors have been associated with various human diseases, including cancer, neurodegenerative diseases, and developmental disorders. For example, mutations in the bHLH transcription factor HES1 are associated with Hirschsprung's disease, a congenital disorder of the colon.

See also

• Transcription (genetics)
• Gene expression
• Protein structure
• DNA binding domain
• E-box