Side-chain assisted ligation in protein synthesis.

Chemical ligation methods for the assembly of functional proteins continue to advance our basic understanding of protein structure and function. In this work, we report on our progress towards the full synthesis of HIV-1 Tat utilizing our newly developed ligation method; side-chain assisted ligation. The HIV-1 Tat was assembled from three fragments wherein the two thioester peptides were synthesized efficiently using the side-chain anchoring strategy following Fmoc-SPPS. The side-chain assisted ligation step was efficient and provided the ligation product in good yield. Following this step, native chemical ligation was used to fully assemble the HIV-1 Tat protein. Although the removal of the auxiliary in small peptides was straightforward, in the case of HIV-1 Tat this step was inefficient thus hampering the completion of the synthesis.