Light-induced pulsed dipolar EPR spectroscopy for distance and orientation analysis

Erythrosin B as a New Photoswitchable Spin Label for Light-Induced Pulsed EPR Dipolar Spectroscopy

“…Details on the synthesis and purification of 1 are given in the Materials and Methods section. A sarcosine linker was used instead of the more rigid direct attachment of the EB label to the N-terminus of the peptide via its carboxylate group in order to avoid the formation of the colorless spirolactam form [ 33 ]. This method is advantageous to previously reported strategies with similar chromophores, which involved the use of more expensive para-substituted derivatives of the chromophores as starting materials or introduced longer 5-atom linkers with additional unwanted conformational flexibility [ 22 ].…”

“…The search for new photoswitchable spin labels for LiPDS, which could be attached to proteins that lack intrinsic photoexcitable groups, is an active area of research and a priority for the development of the field. In addition to having the right spectroscopic properties, good candidate labels for structural biology studies must be small, biocompatible, and commercially available in functionalized forms suitable for biolabeling [ 33 ]. Halogenated derivatives of fluorescein, such as eosin Y (EY) and rose Bengal (RB), and thioxanthene-based chromophores, such as ATTO Thio12 (AT), have been proposed as photoswitchable triplet labels based on spectroscopic characterization and DFT calculations [ 34 ] and were subsequently used in LaserIMD studies of the protein oxidoreductase thioredoxin in conjunction with nitroxide labels [ 22 ].…”

Dance with spins: site-directed spin labeling coupled to electron paramagnetic resonance spectroscopy directly inside cells

“…[40][41][42] More recently, a fourth family of photoexcitable spin-labels based on transient triplet-states induced by a laser (LaserIMD, LiDEER) has been designed. 43,44 At the moment of writing, we are still far from seeing the latter approach exploited for cellular applications. However, being both fluorescent and paramagnetic, these spinlabels will allow the spatial localization and the structural characterization of the labeled molecule, using the same biological sample.…”

Increasing the Modulation Depth of GdIII-Based Pulsed Dipolar EPR Spectroscopy (PDS) with Porphyrin–GdIII Laser-Induced Magnetic Dipole Spectroscopy

“…36 A different approach for PDS is taken in laser-induced magnetic dipole spectroscopy (LaserIMD). 37,38 Here, the dipolar coupling between a permanent spin label and a label that is transiently converted into a paramagnetic state through photoexcitation is measured. The Δ|m S | = 1 transition required for PDS is achieved through intersystem crossing from its photoexcited diamagnetic singlet state (S = 0) to the paramagnetic triplet state (S = 1), thereby replacing the microwave pump pulse used in DEER (Figure 1a).…”