Constitutively active mutants of rhodopsin.

Area of Science:

• Biochemistry
• Molecular Biology
• Vision Science

Background:

• Rhodopsin, a key visual pigment, relies on specific amino acids for its function.
• Lysine-296 (Lys-296) and Glutamic acid-113 (Glu-113) are critical for rhodopsin's structure and activity.
• Constitutive activation of opsin, the protein component of rhodopsin, can lead to photoreceptor degeneration.

Purpose of the Study:

• To investigate the role of Lys-296 and Glu-113 in rhodopsin's inactive conformation.
• To understand the mechanism by which mutations in these residues lead to constitutive opsin activation.
• To explore the link between rhodopsin mutations and retinitis pigmentosa.

Main Methods:

• Site-directed mutagenesis of rhodopsin at Lys-296 and Glu-113.
• Assaying opsin's ability to activate transducin in the absence of retinal.
• Analyzing the structural constraints maintaining opsin's inactive state.

Main Results:

• Mutations at Lys-296 and Glu-113 result in constitutive activation of opsin.
• A salt bridge between Lys-296 and Glu-113 appears to maintain opsin in an inactive conformation.
• The K296E mutant was identified in a retinitis pigmentosa family, linking the mutation to photoreceptor degeneration.

Conclusions:

• Opsin's inactive conformation is stabilized by a salt bridge between Lys-296 and Glu-113.
• Constitutive opsin activation due to mutations may underlie photoreceptor cell death in retinitis pigmentosa.
• Understanding these molecular mechanisms is crucial for developing therapies for vision disorders.