Synthesis of [U-13C, 15N]-cysteine hydrochloride: an important tool for heteronuclear, multi-dimensional NMR studies of proteins

Protein structure determination by modern NMR techniques is greatly facilitated using 15N- and 13C-labeled proteins. Labeling of proteins that are overexpressed in mammalian cells is a difficult task that requires a growth medium consisting of algal hydrolysates supplemented with labeled amino acids. Although most of the amino acids can be obtained to prepare an isotopically labeled growth medium for mammalian cells,[U-13C,15N]-cysteine is not available, hampering the backbone and cysteine side-chain assignments and structure determination in the vicinity of the cysteine residues. A synthesis of D,L-[U-13C,15N]cysteine hydrochloride in good overall yield is described which makes use of readily available 15N-and 13C-labeled starting materials and will facilitate heteronuclear multidimensional NMR studies of proteins that are overexpressed in mammalian cells. (author)