Observation of early events in the photoactivation of Myxobacterial phytochrome using time-resolved serial femtosecond crystallography

Résumé fourni par la source

Myxobacteria are non-photosynthetic, soil-dwelling bacteria distinguished by a multicellular stage in their life cycle known as fruiting bodies that are stimulated by light. Myxobacterial phytochromes are candidates for the perception of red-light. The mechanism how light is perceived and converted to a physiological response is unknown. Here, time-resolved serial femtosecond crystallographic (TR-SFX) experiments were conducted on microcrystals of the photosensory core module of the Stigmatella aurantiaca bacteriophytochrome 2 (SaBphP2). Initial events of the Z to E isomerization reaction of the covalently bound, open-chain tetrapyrrole biliverdin (BV) chromophore were determined. At 3 ps after light activation, the BV ring-D assumes a configuration needed for the isomerization. At 100 ps, a mixture of BV in the Z or E configuration is observed in subunit A, while in the other subunit the chromophore remains in the Z configuration. In conjunction with prior results, these structures reveal the molecular mechanism of phytochrome activation in the photomorphogenesis of the myxobacteria and provide the molecular foundation for physiological responses to red light in other bacteria. Although the photocycle of the photosensory core module of the Stigmatella aurantiaca bacteriophytochrome 2 (SaBphP2) has been extensively studied, its early dynamics have not been fully resolved. Here, the authors use time-resolved serial femtosecond crystallography to probe the associated picosecond events and report on the relative population of Z and E isomers after light activation.

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