Structurally， butelase 1 is a cysteine protease of the asparaginyl endoprotease (AEP) family， but functionally， it displays intense Asn/Asp-specific (Asx) ligase activity and is virtually devoid of protease activity. Butelase 1 recognizes specifically a C-terminal Asx-containing tripeptide motif， Asx-His-Val， to form an Asx-Xaa peptide bond (Xaa?=?any amino acid)， either intramolecularly or intermolecularly， resulting in cyclic peptides or site-specific modified peptides/proteins， respectively. Our work in the past 4?years has validated that butelase 1 is a potent and versatile tool for peptide and protein modification. Here we describe our protocols using butelase 1 for efficient and site-speci... More
Structurally， butelase 1 is a cysteine protease of the asparaginyl endoprotease (AEP) family， but functionally， it displays intense Asn/Asp-specific (Asx) ligase activity and is virtually devoid of protease activity. Butelase 1 recognizes specifically a C-terminal Asx-containing tripeptide motif， Asx-His-Val， to form an Asx-Xaa peptide bond (Xaa?=?any amino acid)， either intramolecularly or intermolecularly， resulting in cyclic peptides or site-specific modified peptides/proteins， respectively. Our work in the past 4?years has validated that butelase 1 is a potent and versatile tool for peptide and protein modification. Here we describe our protocols using butelase 1 for efficient and site-specific peptide and protein ligation， N-terminal labeling， preparation of thioesters， and bioconjugation of dendrimers. Additionally， we provide an example using butelase 1 for protein cyclization in combination with genetic code expansion in order to incorporate unnatural building blocks.
