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Expressed Protein Ligation at Methionine: N-Terminal Attachment of Homocysteine, Ligation, and Masking


  • This work was supported by funding from the University of Pennsylvania and the Searle Scholars Program (10-SSP-214 to E.J.P.). T.T. was supported by a fellowship from the Japan Society for the Promotion of Science (JSPS). We thank Rakesh Kohli for assistance with HRMS (NIH RR-023444) and MALDI-MS (supported by NSF MRI-0820996).


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A useful handle: One major limitation of protein semi-synthesis is the need for Cys at the ligation site in native chemical ligation reactions. It is shown that a transferase enzyme can deliver homocysteine to the N-terminus of an expressed protein (see scheme). Homocysteine can be used in a ligation reaction and then converted to Met. This allows one to use the MetArg or MetLys motif as a point of disconnection in semi-synthesis.

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