Phytochrome from photochemistry to signalling: MAS NMR studies of Cph1 structure/function at atomic resolution

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Plant phytochromes are red/far-red photochromic biliprotein photoreceptors that primarily act as master transcriptional regulators, thereby switching light-dependent developmental processes throughout the plant lifecycle including germination and flowering. How the phytochrome molecule itself actually works is, however, largely unclear. The cyanobacterial phytochrome Cph1 shows particularly close similarities to plant phytochromes and thus represents a most useful model for studies of phytochrome molecular function. Additionally, however, Cph1 is a photon-regulated histidine kinase whose functional mechanism pertains to that of “two-component” sensory kinases in general, including those of medically-important pathogens. In this project we will develop and use advanced magic-angle spinning NMR methods not only to identify atomic neighbours but to derive highly-accurate interatomic distances within Cph1. Complementary to the detailed but largely static structural information obtained from X-ray crystallography, we will produce detailed pictures of functional dynamics in the Cph1 parent states and, with the help of freeze-trapping, photoconversion intermediates over wide timescales. Site-directed mutants will also allow us to manipulate the molecule experimentally. We will focus on regions crucial in the intramolecular signalling process, namely the neighbourhood of the chromophore D-ring and the tongue region of the PHY domain. We also propose to exploit 31P in MAS NMR to study the catalytic ATP-binding domain and its histidine target.