3vic
Green-fluorescent variant of the non-fluorescent chromoprotein Rtms5
Structural highlights
FunctionNFCP_MONEF Thought to play a role in photoprotection of the coral's resident symbiont microalgae's photosystems from photoinhibition caused by high light levels found near the surface of coral reefs.[1] Publication Abstract from PubMedRtms5 is an deep blue weakly fluorescent GFP-like protein ([Formula: see text], 592 nm; [Formula: see text], 630nm; Phi(F), 0.004) that contains a (66)Gln-Tyr-Gly chromophore tripeptide sequence. We investigated the optical properties and structure of two variants, Rtms5(Y67F) and Rtms5(Y67F/H146S) in which the tyrosine at position 67 was substituted by a phenylalanine. Compared to the parent proteins the optical spectra for these new variants were significantly blue-shifted. Rtms5(Y67F) spectra were characterised by two absorbing species ([Formula: see text], 440 nm and 513 nm) and green fluorescence emission ([Formula: see text], 440 nm; [Formula: see text], 508 nm; Phi(F), 0.11), whilst Rtms5(Y67F/H146S) spectra were characterised by a single absorbing species ([Formula: see text], 440 nm) and a relatively high fluorescence quantum yield (Phi(F,) 0.75; [Formula: see text], 440 nm; [Formula: see text], 508 nm). The fluorescence emissions of each variant were remarkably stable over a wide range of pH (3-11). These are the first GFP-like proteins with green emissions (500-520 nm) that do not have a tyrosine at position 67. The X-ray crystal structure of each protein was determined to 2.2 A resolution and showed that the benzylidine ring of the chromophore, similar to the 4-hydroxybenzylidine ring of the Rtms5 parent, is non-coplanar and in the trans conformation. The results of chemical quantum calculations together with the structural data suggested that the 513 nm absorbing species in Rtms5(Y67F) results from an unusual form of the chromophore protonated at the acylimine oxygen. These are the first X-ray crystal structures for fluorescent proteins with a functional chromophore containing a phenylalanine at position 67. A Green Fluorescent Protein Containing a QFG Tri-Peptide Chromophore: Optical Properties and X-Ray Crystal Structure.,Battad JM, Traore DA, Byres E, Rossjohn J, Devenish RJ, Olsen S, Wilce MC, Prescott M PLoS One. 2012;7(10):e47331. doi: 10.1371/journal.pone.0047331. Epub 2012 Oct 10. PMID:23071789[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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