Bacteriophytochromes (BphPs) are red-light photoreceptors found in various photosynthetic and non-photosynthetic bacteria. Members of this protein family play a major role in signal transduction pathways that regulate bacterial growth and development. BphPs are composed of a photosensory module that consists of three domains termed PAS, GAF, and PHY along with a signal effector domain, known as histidine kinase (HK). BphPs utilize covalently attached biliverdin chromophore (BV), a linear tetrapyrrole, as an organic pigment to detect light. BV enables photoconversion between red and far-red light-absorbing states, which results in global structural changes within the protein. These structural changes are not well-understood due to lack of crystal structures of intact BphPs which are also too large for analysis by NMR. Therefore, Atomic Force Microscopy (AFM) has been employed to characterize the structure of the photosensory module and the fully intact BphP, which includes HK, in the light-adapted states. Specifically, we focus on the structural analysis of red-light photoreceptor (SaBphP2) from non-photosynthetic myxobacterium <i>Stigmatella aurantiaca</i>. PeakForce Quantitative Nanomechanical Property Mapping has been used to gain insight into protein structure and dynamics at physiologically relevant conditions and nanometer resolution. Individual dimers of SaBphP2 have been observed on a mica surface in the presence of red light. The size, orientation, and structure of these red-light photoreceptors have been directly compared to models of intact BphPs generated using PyMOL software and X-ray crystallographic structures of similar BphPs. Cross-sectional analysis and total volume measurements of the SaBphP2 dimers are in close agreement with the models.

Structural characterization of red light photoreceptors isolated from <i>Stigmatella aurantiaca</i> using atomic force microscopy

251st National Meeting (2016)

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Structural characterization of red light photoreceptors isolated from Stigmatella aurantiaca using atomic force microscopy