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Understanding GFP chromophore biosynthesis: controlling backbone cyclization and modifying post-translational
David P Barondeau1, Carey J Kassmann, John A Tainer
1Department of Molecular Biology, The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
Biochemistry
|February 9, 2005
Summary
Researchers engineered the green fluorescent protein (GFP) to create a 4-methylidene-imidazole-5-one (MIO) moiety. Structural studies reveal key mechanisms of GFP chromophore formation and MIO biosynthesis, with implications for genetic code expansion.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Engineering
Background:
- The Aequorea victoria green fluorescent protein (GFP) contains a chromophore formed by post-translational modification of amino acids S65, Y66, and G67.
- Histidine ammonia lyase (HAL) utilizes a 4-methylidene-imidazole-5-one (MIO) moiety as its active-site electrophile.
Purpose of the Study:
- To engineer GFP to form an MIO moiety similar to that in HAL.
- To elucidate the structural and mechanistic details of GFP chromophore formation and MIO biosynthesis.
Main Methods:
- Site-directed mutagenesis of GFP to create variants, including S65A Y66S (GFPhal).
- Crystallographic analysis of GFP variants to determine structures.
- Bioinformatic and biochemical analysis of protein scaffold contributions to cyclization.
Main Results:
- Crystallographic structures revealed an aromatic MIO moiety in the GFPhal variant.
- Identified specific mechanisms by which the GFP scaffold promotes backbone cyclization for chromophore formation.
- Highlighted the role of residue R96 in facilitating MIO ring cyclization and stabilizing intermediates.
- Uncovered negative design features in wild-type GFP that favor chromophore formation over alternative conformations.
Conclusions:
- The GFP scaffold actively promotes MIO biosynthesis through precise alignment and energetic stabilization.
- Understanding these mechanisms provides a molecular basis for controlling protein chemistry and chromophore creation.
- This research has potential applications in expanding the genetic code through engineered amino acids.