Site-Selective Enzymatic Labeling of Designed Ankyrin Repeat Proteins Using Protein Farnesyltransferase

Yi Zhang, Shelby Auger, Jonas V. Schaefer, Andreas Plückthun, Mark D. Distefano

Research output: Chapter in Book/Report/Conference proceedingChapter

5 Scopus citations


Affinity agents coupled to a functional moiety play an ever-increasing role in modern medicine, ranging from radiolabeled selective binders in diagnosis to antibody–drug conjugates in targeted therapies. In biomedical research, protein coupling to fluorophores, surfaces and nanoparticles has become an integral part of many procedures. In addition to antibodies, small scaffold proteins with similar target binding properties are being widely explored as alternative targeting moieties. To label these binders of interest with different functional moieties, conventional chemical coupling methods can be employed, but often result in heterogeneously modified protein products. In contrast, enzymatic labeling methods are highly site-specific and efficient. Protein farnesyltransferase (PFTase) catalyzes the transfer of an isoprenoid moiety from farnesyl diphosphate (FPP) to a cysteine residue in a C-terminal CaaX motif at the C-terminus of a protein substrate. The addition of only four amino acid residues minimizes the influence on the native protein structure. In addition, a variety of isoprenoid analogs containing different bioorthogonal functional groups, including azides, alkynes, and aldehydes, have been developed to enable conjugation to various cargos after being incorporated onto the target protein by PFTase. In this protocol, we present a detailed procedure for labeling Designed Ankyrin Repeat Proteins (DARPins) engineered with a C-terminal CVIA sequence using an azide-containing FPP analog by yeast PFTase (yPFTase). In addition, procedures to subsequently conjugate the labeled DARPins to a TAMRA fluorophore using strained-promoted alkyne–azide cycloaddition (SPAAC) reactions as well as the sample preparation to evaluate the target binding ability of the conjugates by flow cytometry are described.

Original languageEnglish (US)
Title of host publicationMethods in Molecular Biology
PublisherHumana Press Inc.
Number of pages13
StatePublished - 2019

Publication series

NameMethods in molecular biology (Clifton, N.J.)
PublisherHumana Press
ISSN (Print)1064-3745

Bibliographical note

Funding Information:
This work was supported by National Institutes of Health (GM084152) and the National Science Foundation (CHE-1359181).

Publisher Copyright:
© Springer Science+Business Media, LLC, part of Springer Nature 2019.


  • DARPins
  • Enzymatic protein labeling
  • Flow cytometry
  • Isoprenoid analogs
  • Protein farnesyltransferase
  • Site-specific conjugation

PubMed: MeSH publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Journal Article
  • Research Support, N.I.H., Extramural


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