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 15 N- and 13 C-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- 13 C, 15 N]-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- 13 C, 15 N]-cysteine hydrochloride in good overall yield is described which makes use of readily available 15 N- and 13 C-labeled starting materials and will facilitate heteronuclear multidimensional NMR studies of proteins that are overexpressed in mammalian cells