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Dissertation/Thesis Abstract

Crystal Structures of the Red-Light Photoreceptor From Photomorphogenic Myxobacterium Stigmatella aurantiaca
by Waltz, Patricia, M.S., Northeastern Illinois University, 2017, 45; 10265263
Abstract (Summary)

Bacteriophytochromes (BphPs) are red-light photoreceptors that regulate light responses in bacteria via reversible photoconversion between red (Pr) and far-red (Pfr) light-absorbing states. BphPs consist of a photosensory module that is composed of the PAS (Per-ARNT-Sim), GAF (cGMP phosphodiesterase/adenyl cyclase/FhlA), and PHY (phytochrome) domains. The PHY domain is covalently linked to a signaling-effector module such as histidine kinase. Wild-type protein from non-photosynthetic myxobacterium Stigmatella aurantiaca (SaBphP1) was purified, crystallized, and the structure of the complete photosensory module was determined at 2.25Å resolution. Unlike classical BphPs, SaBphP1 undergoes limited Pr/Pfr photoconversion in the presence of the PHY domain. Wild-type SaBphP1 lacks a conserved histidine (His) that forms a hydrogen bond with the chromophore in the Pr state in the classical BphPs. A single Thr289His mutation in the chromophore-binding pocket of SaBphP1 results in a complete Pr/Pfr photoconversion. Consequently, we determined the crystal structure of the complete photosensory module for SaBphP1 Thr289His mutant at 2.65Å resolution. Both SaBphP1 crystal structures, solved in the Pr state, reveal how interdomain interactions bring together PAS, GAF and PHY domains to achieve Pr/Pfr photoconversion. In addition, comparison of the structures reveals significant differences in the packing of the PHY domain as well as specific changes in the chromophore binding pocket. We identify key amino acids that stabilize the chromophore in the Pr state and provide structural evidence to support the essential role of the PHY domain in Pr/Pfr photoconversion. Furthermore, we recently determined a room temperature structure of T289H mutant at 3.15Å resolution utilizing XFEL at SACLA in Japan. Overall, the T289H mutant at room temperature crystallizes in the same space group with very similar parameters and packing of the protein reveals similar folding to the cryo temperature structure. Our results highlight local structural changes from the photosensory domain that significantly affect the long, signaling helices at the dimer interface and may impact the spatially distant histidine kinase domain and its activity.

Indexing (document details)
Advisor: Stojkovic, Emina A.
Commitee: Mungre, Shubhangee M., Schirmer, Aaron E.
School: Northeastern Illinois University
Department: Biology
School Location: United States -- Illinois
Source: MAI 56/05M(E), Masters Abstracts International
Subjects: Biology, Cellular biology, Biochemistry
Keywords: Biliverdin, Histidine kinase, Photoreceptor, Phytochromes, Stigmatella aurantiaca, Xfels
Publication Number: 10265263
ISBN: 978-0-355-22666-9
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