Retinol dehydrogenases: membrane-bound enzymes for the visual function.

Area of Science:

• Biochemistry
• Molecular Biology
• Vision Science

Background:

• Retinoid metabolism is vital for vision, involving a cascade of reactions in photoreceptors and retinal pigment epithelium.
• Retinol dehydrogenases (RDHs) are key enzymes in the visual cycle, belonging to the short-chain dehydrogenases/reductases family.
• Light absorption by rhodopsin triggers the isomerization of 11-cis retinal to all-trans retinal, initiating the visual cycle.

Purpose of the Study:

• To review the current knowledge on the functional and structural characteristics of RDHs in the visual cycle.
• To present proposed models for RDH structure, including the common Rossman fold.
• To discuss the role of RDHs as integral or peripheral enzymes and their membrane-binding topology.

Main Methods:

• Bioinformatic tools were utilized to predict the structure of RDHs.
• Analysis of existing literature on RDH function, structure, and knockout models.
• Examination of cofactor preferences (NAD(H)/NADP(H)) influencing enzyme activity.

Main Results:

• RDHs possess similar predicted structures featuring a Rossman fold.
• Enzyme activity direction is determined by cofactor availability and preference.
• A topology model for membrane binding of RDHs via N- and/or C-terminal domains has been proposed.

Conclusions:

• RDHs play critical roles in retinoid metabolism essential for vision.
• Understanding RDH structure and membrane association is key due to hydrophobic substrate interactions.
• Further research into RDHs, including knockout models, will elucidate their precise functions in the visual cycle.