Researchers in the US have developed a new reagent for studying proteins.

The reagent has a biotin affinity tag (red) and a reactive group to capture tyrosine (pale blue)

Shuwei Li and Dexing Zeng at the University of Maryland Biotechnology Institute made the reagent, which they called CILAT (cleavable isobaric labelled affinity tag). It labels peptides produced during proteomic analysis; the study of the structure and functions of proteins in organisms.

The CILAT reagent was designed to combine the benefits of two other labelling methods: ICAT (isotope-coded affinity tag) and iTRAQ (isobaric tags for relative and absolute quantitation). These are used to measure levels of proteins in different biological systems, for example, comparing diseased and healthy cells, and to find diagnostic biomarkers for a disease.

ICAT reagents attach to the cysteine residues in the peptides. They also have an affinity tag at one end which means that they can be separated from unlabelled peptides. The CILAT reagent was used similarly, but specifically labelled tyrosine, a more abundant residue in proteins.

Like the iTRAQ reagents there are two forms of the CILAT reagent, both containing carbon-13, but in different positions. When the labelled peptides were studied by mass spectrometry they fragmented to give 'reporter ions' of different mass, depending on which form of CILAT was used. When two biological systems are labelled differently and then mixed together, the amounts of certain peptides can be compared for the two systems by looking at the relative intensities of the reporter ions. Li and Zeng also ran mass spectrometry experiments with minimal fragmentation to work out the peptide sequences.

Steven Gygi at Harvard Medical School, US, welcomed the development: 'This new CILAT reagent by Li and Zeng encapsulates the promise of both ICAT and iTRAQ reagents,' he said.

Li outlined their future plans: 'Hopefully, we can develop a simple and robust protocol so that other labs can easily use our technique,' he said.

Rachel Warfield