Amino acid-selective isotope labeling of proteins for nuclear magnetic resonance study: proteins secreted by Brevibacillus choshinensis.

Abstract Here we report the first application of amino acid-type selective (AATS) isotope labeling of a recombinant protein secreted by Brevibacillus choshinensis for a nuclear magnetic resonance (NMR) study. To prepare the 15 N-AATS-labeled protein, the transformed B. choshinensis was cultured in 15 N-labeled amino acid-containing C.H.L. medium, which is commonly used in the Escherichia coli expression system. The analyses of the 1 H- 15 N heteronuclear single quantum coherence (HSQC) spectra of the secreted proteins with a 15 N-labeled amino acid demonstrated that alanine, arginine, asparagine, cysteine, glutamine, histidine, lysine, methionine, and valine are suitable for selective labeling, although acidic and aromatic amino acids are not suitable. The 15 N labeling for glycine, isoleucine, leucine, serine, and threonine resulted in scrambling to specific amino acids. These results indicate that the B. choshinensis expression system is an alternative tool for AATS labeling of recombinant proteins, especially secretory proteins, for NMR analyses.