TY - JOUR
T1 - Photoactivation mechanism of PAmCherry based on crystal structures of the protein in the dark and fluorescent states
AU - Subach, Fedor V.
AU - Malashkevich, Vladimir N.
AU - Zencheck, Wendy D.
AU - Xiao, Hui
AU - Filonov, Grigory S.
AU - Almo, Steven C.
AU - Verkhusha, Vladislav V.
PY - 2009/12/15
Y1 - 2009/12/15
N2 - Photoactivatable fluorescent proteins (PAFPs) are required for super-resolution imaging of live cells. Recently, the first red PAFP, PAmCherry1, was reported, which complements the photoactivatable GFP by providing a red super-resolution color. PAmCherry1 is originally "dark" but exhibits red fluorescence after UV-violet light irradiation. To define the structural basis of PAmCherry1 photoactivation, we determined its crystal structure in the dark and red fluorescent states at 1.50 Å and 1.65 Å, respectively. The non-coplanar structure of the chromophore in the dark PAmChery1 suggests the presence of an N-acylimine functionality and a single non-oxidized Cα-Cβ bond in the Tyr-67 side chain in the cyclized Met-66-Tyr-67-Gly-68 tripeptide. MS data of the chromophore-bearing peptide indicates the loss of 20 Da upon maturation, whereas tandemMSreveals the Cα - N bond in Met-66 is oxidized. These data indicate that PAmCherry1 in the dark state possesses the chromophore N-[(E)-(5-hydroxy-1H-imidazol-2-yl)methylidene]acetamide, which, to our knowledge, has not been previously observed in PAFPs. The photoactivated PAmCherry1 exhibits a non-coplanar anionic DsRed-like chromophore but in the trans configuration. Based on the crystallographic analysis, MS data, and biochemical analysis of the PAmCherry1 mutants, we propose the detailed photoactivation mechanism. In this mechanism, the excited-state PAmCherry1 chromophore acts as the oxidant to release CO2 molecule from Glu-215 via a Koble-like radical reaction. The Glu-215 decarboxylation directs the carbanion formation resulting in the oxidation of the Tyr-67 C α-Cβbond. The double bond extends the π-conjugation between the phenolic ring of Tyr-67, the imidazolone, and the N-acylimine, resulting in the red fluorescent chromophore.
AB - Photoactivatable fluorescent proteins (PAFPs) are required for super-resolution imaging of live cells. Recently, the first red PAFP, PAmCherry1, was reported, which complements the photoactivatable GFP by providing a red super-resolution color. PAmCherry1 is originally "dark" but exhibits red fluorescence after UV-violet light irradiation. To define the structural basis of PAmCherry1 photoactivation, we determined its crystal structure in the dark and red fluorescent states at 1.50 Å and 1.65 Å, respectively. The non-coplanar structure of the chromophore in the dark PAmChery1 suggests the presence of an N-acylimine functionality and a single non-oxidized Cα-Cβ bond in the Tyr-67 side chain in the cyclized Met-66-Tyr-67-Gly-68 tripeptide. MS data of the chromophore-bearing peptide indicates the loss of 20 Da upon maturation, whereas tandemMSreveals the Cα - N bond in Met-66 is oxidized. These data indicate that PAmCherry1 in the dark state possesses the chromophore N-[(E)-(5-hydroxy-1H-imidazol-2-yl)methylidene]acetamide, which, to our knowledge, has not been previously observed in PAFPs. The photoactivated PAmCherry1 exhibits a non-coplanar anionic DsRed-like chromophore but in the trans configuration. Based on the crystallographic analysis, MS data, and biochemical analysis of the PAmCherry1 mutants, we propose the detailed photoactivation mechanism. In this mechanism, the excited-state PAmCherry1 chromophore acts as the oxidant to release CO2 molecule from Glu-215 via a Koble-like radical reaction. The Glu-215 decarboxylation directs the carbanion formation resulting in the oxidation of the Tyr-67 C α-Cβbond. The double bond extends the π-conjugation between the phenolic ring of Tyr-67, the imidazolone, and the N-acylimine, resulting in the red fluorescent chromophore.
KW - Chromophore
KW - Localization microscopy
KW - Photoconversion
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U2 - 10.1073/pnas.0909204106
DO - 10.1073/pnas.0909204106
M3 - Article
C2 - 19934036
AN - SCOPUS:75849129809
SN - 0027-8424
VL - 106
SP - 21097
EP - 21102
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 50
ER -