Isotopic labeling of proteins by utilizing photosynthetic bacteria.

Determination of the three-dimensional solution structures of proteins is essential to the understanding of protein functions and interactions which could lead to new pharmaceutical developments. Novel high-resolution nuclear magnetic resonance (NMR) techniques have emerged and provided powerful tools to analyze structures of proteins of up to »900 kDa molecular weight [1]. These state-of-the-art experiments require the use of recombinant proteins labeled with stable isotopes, most notably 15N, 13C, and 2H. The most widely used method to obtain isotope-enriched proteins has been through the expression of proteins from bacterial cells grown in minimal media containing C-enriched glucose and 15N-enriched salts. Although this method has proven successful in the determination of many protein solution structures by NMR, there are limitations associated with using minimal media for protein expression. Growth rates and protein expression can be increased with the use of “rich media” products that contain more complex substrates rather than simple sugars and nitrogen salts [2]. The rich media that contain mixtures of amino acids, peptides, nuclear acids, and complex carbohydrates can decrease doubling times and increase total protein expression. As a result, these media improve eYciency of the total labeling process and increase the yields of the proteins of interest.