Cyan fluorescent proteins derived from mNeonGreen

Excited State Vibrational Dynamics Reveals a Photocycle That Enhances the Photostability of the TagRFP-T Fluorescent Protein

High photostability is a desirable property of fluorescent proteins (FPs) for imaging, yet its molecular basis is poorly understood. We performed ultrafast spectroscopy on TagRFP and its 9-fold more photostable variant TagRFP-T (TagRFP S158T) to characterize their initial photoreactions. We find significant differences in their electronic and vibrational dynamics, including faster excited-state proton transfer and transient changes in the frequency of the v520 mode in the excited electronic state of TagRFP-T. The frequency of v520, which is sensitive to chromophore planarity, downshifts within 0.58 ps and recovers within 0.87 ps. This vibrational mode modulates the distance from the chromophore phenoxy to the side chain of residue N143, which we suggest can trigger cis/trans photoisomerization. In TagRFP, the dynamics of v520 is missing, and this FP therefore lacks an important channel for chromophore isomerization. These dynamics are likely to be a key mechanism differentiating the photostability of the two FPs.

AgTx2-GFP, Fluorescent Blocker Targeting Pharmacologically Important Kv1.x (x = 1, 3, 6) Channels

The growing interest in potassium channels as pharmacological targets has stimulated the development of their fluorescent ligands (including genetically encoded peptide toxins fused with fluorescent proteins) for analytical and imaging applications. We report on the properties of agitoxin 2 C-terminally fused with enhanced GFP (AgTx2-GFP) as one of the most active genetically encoded fluorescent ligands of potassium voltage-gated K_v1.x (x = 1, 3, 6) channels. AgTx2-GFP possesses subnanomolar affinities for hybrid KcsA-K_v1.x (x = 3, 6) channels and a low nanomolar affinity to KcsA-K_v1.1 with moderate dependence on pH in the 7.0-8.0 range. Electrophysiological studies on oocytes showed a pore-blocking activity of AgTx2-GFP at low nanomolar concentrations for K_v1.x (x = 1, 3, 6) channels and at micromolar concentrations for K_v1.2. AgTx2-GFP bound to K_v1.3 at the membranes of mammalian cells with a dissociation constant of 3.4 ± 0.8 nM, providing fluorescent imaging of the channel membranous distribution, and this binding depended weakly on the channel state (open or closed). AgTx2-GFP can be used in combination with hybrid KcsA-K_v1.x (x = 1, 3, 6) channels on the membranes of E. coli spheroplasts or with K_v1.3 channels on the membranes of mammalian cells for the search and study of nonlabeled peptide pore blockers, including measurement of their affinity.

Extension of the short wavelength side of fluorescent proteins using hydrated chromophores, and its application

To perform correlation analysis between different physiological parameters using fluorescent protein-based functional probes, diversification of wavelength properties of fluorescent proteins is underway. However, the shortest emission wavelength of fluorescent proteins has not been updated for more than 10 years. Here, we report the development of Sumire, a fluorescent protein emitting 414 nm violet fluorescence from a hydrated chromophore. The Sumire’s fluorescence property allows for the creation of FRET probes that can be used simultaneously with CFP-YFP based FRET probes for multi-parameter analysis.

A violet fluorescent protein with emission wavelength 414 nm is engineered.