Biology subjects

Kurttila, M.

Publications and source records attributed to Kurttila, M..

4 recordsLinked to original sources

bioRxiv2026

Dimensionally traceable 3D microstructures for multimodal microscope calibration

High-resolution microscopy techniques are used across research and industry to analyse biological systems, from biomolecules to subcellular organelles, multicellular models and tissues. As multimodal imaging workflows and quantitative analysis of bioimaging data become increasingly widespread, there is a growing need for materials and methods to calibrate imaging systems and evaluate the fidelity of generated image data. Here, we present three-dimensional microscopy phantoms fabricated using two-photon photolithography from transparent resins that exhibit both broadband visible autofluorescence and Raman scattering across the fingerprint and C-H stretching regions. Suitable for analysis using optical profilometry, the phantoms were dimensionally calibrated with SI traceability using a metrological confocal microscope. Immersible in air and common aqueous imaging media, the phantoms are compatible with a wide variety of optical microscopy techniques, including one and two-photon excited fluorescence and coherent Raman scattering microscopy. We employed a forked wedge design to validate image deconvolution results and a stacked lattice phantom to recover image distortion matrices under realistic biological imaging conditions. We demonstrate the impact of correcting chromatic offsets and axial scaling errors for a representative application: analysis of a cell seeded scaffold using confocal laser scanning fluorescence microscopy. These phantoms provide a versatile platform for calibration, quality control and validation of multimodal imaging pipelines and improved quantitative optical microscopy.

bioengineering↗

bioRxiv2025

Environmental dipolar relaxation during excited state proton transfer in Green Fluorescent Protein

Engineered variants of Green Fluorescent Protein (GFP) are in widespread use as genetically-encoded labels for biological imaging. Excitation of its neutral phenolic ground state chromophore populates an emissive anionic phenolate state via excited state proton transfer (ESPT) to E222 along a molecular wire. Computational studies indicate that ESPT fits to an electronically adiabatic rate expression. Although reactions that operate close to the adiabatic limit can be sensitive to environmental dipolar relaxation, little is known about the role of such relaxation during ESPT in GFP. Here, we present the first experimental evidence that dipolar relaxation of the protein matrix occurs during ESPT in response to the change in electron density distribution in the excited state GFP chromophore and is a key determinant of the reaction pathway. Using fluorescence spectroscopy, we excited along the red edge of the neutral phenolic ground state absorption band of several GFP variants with differing chromophore environments. Instead of resulting in a significant red shift of the centre of spectral mass (CSM) of the emission spectra common for biological chromophores such as tryptophan, the CSM of each GFP variant remains almost unchanged as a function of excitation wavelength. This is consistent with each sub-population that is selectively excited along the red edge reaching the same, fully relaxed state before emission of a photon. The kinetics of environmental dipolar relaxation are therefore on the same sub-nanosecond timescale as ESPT, which provides an explanation for its adiabatic nature and could inform the rational design of novel fluorescent proteins with tailored photophysics.

biophysics↗

bioRxiv2025

How the Drosophila Cryptochrome C-terminus mediates magnetosensitivity

The Earths magnetic field plays an important role in the seasonal migrations of many species of animals. A Cryptochrome (CRY)-based radical pair mechanism (RPM) has been suggested to underlie the mechanistic basis of animal magnetosensitivity and navigation. The quantum spin state of a radical pair involving flavin adenine dinucleotide (FAD) bound to CRY in the canonical pocket is sensitive to external magnetic fields that can alter the signalling concentration of activated CRY1-5. However, several experimental observations challenge this model including the finding that the C-terminal fragment of Drosophila CRY (DmCRY), which lacks any canonical FAD binding pocket, and human CRY2, which lacks affinity for FAD, are sufficient to support magnetosensitivity6-9. Here, we use all-atom molecular dynamic (MD) simulations, alongside in vitro and in vivo analyses to reveal that the C-terminus of Drosophila CRY (DmCRY-CT) binds FAD. FAD binding is required for transduction of a magnetic signal within cells, and, in vitro, initiates formation of high molecular weight DmCRY-CT oligomers, including large insoluble aggregates reminiscent of CRY photobodies observed in plants10-14. These results provide a plausible mechanistic basis for several experimental observations that have reported non-canonical magnetosensitivity in animals.

biochemistry↗

bioRxiv2019

The primary structural photoresponse of phytochrome proteins captured by a femtosecond X-ray laser

Phytochrome proteins control the growth, reproduction, and photosynthesis of plants, fungi, and bacteria. Light is detected by a bilin cofactor, but it remains elusive how this leads to activation of the protein through structural changes. We present serial femtosecond X-ray crystallographic data of the chromophore-binding domains of a bacterial phytochrome at delay times of 1 ps and 10 ps after photoexcitation. The structures reveal a twist of the D-ring, which lead to partial detachment of the chromophore from the protein. Unexpectedly, the conserved so-called pyrrole water is photodissociated from the chromophore, concomitant with movement of the A-ring and a key signalling aspartate. The changes are wired together by ultrafast backbone and water movements around the chromophore, channeling them into signal transduction towards the output domains. We suggest that the water dissociation is key to the phytochrome photoresponse, explaining the earliest steps of how plants, fungi and bacteria sense red light.

biophysics↗