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Sequential phosphorylation of rhodopsin at multiple sites
H Ohguro1, K Palczewski, L H Ericsson
1Department of Ophthalmology, University of Washington, Seattle 98195.
Biochemistry
|June 1, 1993
Summary
This study identifies key phosphorylation sites on rhodopsin during phototransduction quenching. It reveals the initial phosphorylation site and subsequent residues, aiding understanding of rhodopsin kinase action.
Area of Science:
- Molecular Biology
- Biochemistry
- Vision Science
Background:
- Phototransduction involves rhodopsin phosphorylation at multiple serine and threonine residues.
- Rhodopsin kinase phosphorylates rhodopsin, primarily in the C-terminal region.
- Kinetics and specific residues of rhodopsin phosphorylation were previously unknown.
Purpose of the Study:
- To determine the kinetics and identify specific phosphorylated residues in rhodopsin.
- To elucidate the sequential phosphorylation events in the C-terminal region of rhodopsin.
Main Methods:
- Proteolysis of rhodopsin with endoproteinase Asp-N to isolate the C-terminal peptide.
- Subdigestion of the peptide followed by electrospray mass spectrometry.
- Analysis of mono-, di-, and triphosphorylated peptides to identify phosphorylation sites.
Main Results:
- The major initial phosphorylation site was identified as 338Ser.
- Subsequent phosphorylation occurred at 343Ser or 336Thr residues.
- These three residues are key phosphorylation sites in the C-terminal region of rhodopsin.
Conclusions:
- The identified phosphorylation sites (338Ser, 343Ser/336Thr) are crucial for rhodopsin function during phototransduction quenching.
- Understanding the kinetics of phosphorylation enhances knowledge of rhodopsin kinase mechanism and functional significance.