Prof. Konstantin Lukyanov, Inst. Bioorg Chem., Moscow Russia

Fluorescent proteins: Selfish catalytic reactors or photochemical partners?

The study and applications of fluorescent proteins has gone a long way from a subject of highly specialized research to a widely known and indispensable tool for in vivo labeling, and from a single known member-Green Fluorescent Protein from Aequorea victoriato hundreds of natural proteins of different colors with still poorly studied phylogeny and biological significance [1]. A unique property of GFP-like proteins is their ability to form a chromophore by auto-catalyzed modifications of internal amino acids without requiring external enzymes, cofactors or substrates other than molecular oxygen. The β-barrel of fluorescent proteins acts as a “chemical reactor” providing all the required catalytic groups for several reactions resulting in a mature chromophore buried within a protein globule. A number of chromophore structures determining spectral diversity of wild type and mutant GFP-like proteins have characterized by various methods. In particular, the chemical synthesis of model compounds corresponding to natural chromophores of fluorescent proteins and their analogs has provided important details on their chemical and spectral properties [2, 3]. Still, we are far from a clear understanding of the mechanisms of chromophore formation in fluorescent proteins. Thus fluorescent proteins have a complex internal “selfish” chemistry and photochemistry, but seem to be inert to external molecules, acting simply as passive light absorbers/emitters. This generally accepted chemical inertness of fluorescent proteins was challenged recently, when we discovered the ability of GFPs to act as light-induced electron donors in photochemical reactions with various electron acceptors, including biologically relevant ones such as FAD, NAD+ and cytochrome c [4]. Moreover, this process accompanying the green-to-red GFP photoconversion can be observed in living cells without additional treatment. This observation has important consequences for practical applications of fluorescent proteins as well as for our understanding of evolution and biology of this protein family.

1. Chudakov DM, Lukyanov S, Lukyanov KA. Fluorescent proteins as a toolkit for in vivo imaging. Trends Biotechnol. 2005, 23, 605-613.
2. Yampolsky IV, Kislukhin AA, Amatov TT, Shcherbo D, Potapov VK, Lukyanov S, Lukyanov KA. Synthesis and properties of the red chromophore of the green-to-red photoconvertible fluorescent protein Kaede and its analogs. Bioorg. Chem. 2008, 36, 94-104.
3. Yampolsky IV, Balashova TA, Lukyanov K.A. Synthesis and spectral and chemical properties of the yellow fluorescent protein zFP538 chromophore. Biochemistry 2009, 48, 8077-8082.
4. Bogdanov AM, Mishin AS, Yampolsky IV, Belousov VV, Chudakov DM, Subach FV, Verkhusha VV, Lukyanov S, Lukyanov KA. Green fluorescent proteins are light-induced electron donors. Nat. Chem. Biol. 2009, 5, 459-461.

For more information contact Prof. Laren Tolbert (404-894-4093) or Dr. Kyril Solntsev (404-385-3117).