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Protein conformational changes in obelin shown by 15N-HSQC nuclear magnetic resonance John Lee*1; JN Glushka1; SS Markova1,2; ES Vysotski1,2 (1) Dept. of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, 30602, USA; (2) IBP, Russian Academy of Sciences, 660036 Krasnoyarsk      *(jlee@arches.uga.edu) Apo-obelin from Obelia longissima has been hyper-expressed suitable for isotope enrichment in defined medium. Two-dimensional 15N-HSQC experiments at 800 MHz are used to detect solution structural changes of the protein in its various forms, revealed by the chemical shifts of the peptide N and H atoms. The solution structure of the apoprotein is random but on the addition of Ca++ many resonances now appear more dispersed, indicative of a partially folded conformation. The intensities of these resonances are highly variable, characteristic of dynamic flexibility. For obelin "charged" with coelenterazine, the HSQC spectrum now indicates a rigid well-folded solution structure because the resonances are well dispersed and of uniform intensity. The NMR-derived solution secondary structure is consistent with its recently determined crystal structure. On discharging the obelin with Ca++ the HSQC changes somewhat, although the resonances remain uniform in intensity and well dispersed, some with chemical shifts little changed from obelin. The obelin to discharged obelin conformational change could resemble that known for calmodulin on binding Ca++, although in the opposite direction. Supported by ONR and RAS. [Poster: lee.john.23232]

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