Rapid quantification of tyrosine sulfation in therapeutic proteins

Protein tyrosine sulfation (Tyr-O-SO3) is a common post-translational modification (PTM), which is important for protein function. Absolute quantitation of Tyr-O-SO3 in recombinant therapeutic proteins has been challenging. We report here an MRM method used for absolute quantitation of Tyr-O-SO3 in the hydrolysate of a recombinant Fc-fusion protein. Quantitation is achieved by monitoring the sum of two transitions: the loss of carboxylic acid from tyrosine sulfate (major transition) and sulfate group from tyrosine sulfate sodium salt. The method exhibits a good sensitivity with a limit of quantitation of 1.4 ng/mL, linearity over three orders of magnitude, good repeatability, precision and accuracy.