Orchestration of signaling by structural disorder in class 1 cytokine receptors.

BACKGROUND: Class 1 cytokine receptors (C1CRs) are single-pass transmembrane proteins responsible for transmitting signals between the outside and the inside of cells. Remarkably, they orchestrate key biological processes such as proliferation, differentiation, immunity and growth through long disordered intracellular domains (ICDs), but without having intrinsic kinase activity. Despite these key roles, their characteristics remain rudimentarily understood. METHODS: The current paper asks the question of why disorder has evolved to govern signaling of C1CRs by reviewing the literature in combination with new sequence and biophysical analyses of chain properties across the family. RESULTS: We uncover that the C1CR-ICDs are fully disordered and brimming with SLiMs. Many of these short linear motifs (SLiMs) are overlapping, jointly signifying a complex regulation of interactions, including network rewiring by isoforms. The C1CR-ICDs have unique properties that distinguish them from most IDPs and we forward the perception that the C1CR-ICDs are far from simple strings with constitutively bound kinases. Rather, they carry both organizational and operational features left uncovered within their disorder, including mechanisms and complexities of regulatory functions. CONCLUSIONS: Critically, the understanding of the fascinating ability of these long, completely disordered chains to orchestrate complex cellular signaling pathways is still in its infancy, and we urge a perceptional shift away from the current simplistic view towards uncovering their full functionalities and potential. Video abstract.

Photochemical Mechanism of an Atypical Algal Phytochrome.

Phytochromes are bilin-containing photoreceptors that are typically sensitive to the red/far-red region of the visible spectrum. Recently, phytochromes from certain eukaryotic algae have become attractive targets for optogenetic applications because of their unique ability to respond to multiple wavelengths of light. Herein, a combination of time-resolved spectroscopy and structural approaches across picosecond to second timescales have been used to map photochemical mechanisms and structural changes in this atypical group of phytochromes. The photochemistry of an orange/far-red light-sensitive algal phytochrome from Dolihomastix tenuilepis has been investigated by using a combination of visible, IR and X-ray scattering probes. The entire photocycle, correlated with accompanying structural changes in the cofactor/protein, are reported. This study identifies a complex photocycle for this atypical phytochrome. It also highlights a need to combine outcomes from a range of biophysical approaches to unravel complex photochemical and macromolecular processes in multi-domain photoreceptor proteins that are the basis of biological light-mediated signalling.

Instrument-model refinement in normalized reciprocal-vector space for X-ray Laue diffraction.

A simple yet efficient instrument-model refinement method for X-ray diffraction data is presented and discussed. The method is based on least-squares minimization of differences between respective normalized (i.e. unit length) reciprocal vectors computed for adjacent frames. The approach was primarily designed to work with synchrotron X-ray Laue diffraction data collected for small-molecule single-crystal samples. The method has been shown to work well on both simulated and experimental data. Tests performed on simulated data sets for small-molecule and protein crystals confirmed the validity of the proposed instrument-model refinement approach. Finally, examination of data sets collected at both BioCARS 14-ID-B (Advanced Photon Source) and ID09 (European Synchrotron Radiation Facility) beamlines indicated that the approach is capable of retrieving goniometer parameters (e.g. detector distance or primary X-ray beam centre) reliably, even when their initial estimates are rather inaccurate.

Light-induced structural changes in a full-length cyanobacterial phytochrome probed by time-resolved X-ray scattering.

Phytochromes are photoreceptor proteins that transmit a light signal from a photosensory region to an output domain. Photoconversion involves protein conformational changes whose nature is not fully understood. Here, we use time-resolved X-ray scattering and optical spectroscopy to study the kinetics of structural changes in a full-length cyanobacterial phytochrome and in a truncated form with no output domain. X-ray and spectroscopic signals on the µs/ms timescale are largely independent of the presence of the output domain. On longer time-scales, large differences between the full-length and truncated proteins indicate the timeframe during which the structural transition is transmitted from the photosensory region to the output domain and represent a large quaternary motion. The suggested independence of the photosensory-region dynamics on the µs/ms timescale defines a time window in which the photoreaction can be characterized (e.g. for optogenetic design) independently of the nature of the engineered output domain.