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Schiff-base deprotonation is mandatory for light-dependent rhodopsin phosphorylation
1Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115.
The Biochemical Journal
|December 1, 1989
Summary
Active-site Schiff base deprotonation is essential for rhodopsin kinase phosphorylation of photolyzed rhodopsin. This finding identifies metarhodopsin II and III as the primary substrates for rhodopsin kinase activity.
Area of Science:
- Biochemistry
- Photochemistry
- Molecular Biology
Background:
- Light absorption by rhodopsin initiates a signaling cascade involving transducin activation.
- Rhodopsin kinase terminates signaling by phosphorylating activated rhodopsin (R*).
- Previous studies linked Schiff base deprotonation to R* formation and metarhodopsin II appearance.
Purpose of the Study:
- To investigate the role of active-site Schiff base deprotonation in rhodopsin phosphorylation.
- To determine which photolyzed rhodopsin intermediates are substrates for rhodopsin kinase.
Main Methods:
- Reductive dimethylation of rhodopsin's lysine residues to create permethylated rhodopsin (PMRh).
- Monomethylation of PMRh's active-site lysine to yield active-site-methylated rhodopsin (AMRh).
- Assessing phosphorylation susceptibility of photolyzed rhodopsin derivatives.
Main Results:
- Active-site Schiff base deprotonation is mandatory for forming the rhodopsin intermediate phosphorylated by rhodopsin kinase.
- This implies that metarhodopsin II and potentially metarhodopsin III are the direct substrates for rhodopsin kinase.
Conclusions:
- Schiff base deprotonation is a critical step not only for transducin activation but also for preparing rhodopsin for inactivation by rhodopsin kinase.
- The findings refine our understanding of the rhodopsin photocycle and its regulation.