217Synthetic Biology: Parts, Devices and Applications, First Edition. Edited by Christina Smolke.
© 2018 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2018 by Wiley-VCH Verlag GmbH & Co. KGaA.
11
11.1 Introduction Sonja Billerbeck
Small peptides, with as few as 6 aa’s (amino acids), can already bear a variety of
functionalities for large areas of application. A prime example is peptides that
bind fluorophores for color labeling of proteins. Established over 20 years ago,
the fusion to fluorescent proteins revolutionized our ability to equip a protein
with optical traits to follow its behavior in vivo [1]. Although fluorescent pro-
teins persist as indispensable tools for in vivo imaging, their large size can in
certain cases interfere with a protein’s function. Small peptide tags, which
directly bind fluorophores, have therefore shifted into focus and have proven to
be of decisive importance for visualizing and characterizing biological systems
and processes in vivo and in vitro [2]. Besides imaging, other important applica-
tions of small functional peptides include affinity tags for protein purification
and interaction studies or peptides that serve as substrates for proteolytic
activities, enabling the control over protein turnover for synthetic biology
applications [3–5].
Besides such applications more common in basic research, small peptides have
proven important as pharmaceutically relevant agents. Small antimicrobial
peptides show potential as novel broad‐range antibiotics and are already used in
food industry, while the immune modulatory effects of peptides in humans point
toward applications as new immune therapeutic agents [6]. Peptide epitopes or
carbohydrate‐mimicking peptides (CMPs), when inserted into a protective
protein scaffold, show potential to turn into novel vaccines [7, 8]. To this end, not
the modified protein is central but rather the peptide itself with the protein being
used as a mere scaffold.
Traditionally, functional peptides are simply stitched onto either the N‐ or
C‐terminus of a protein. However, it is often essential to insert the peptide into
the middle of the protein at a permissive site, which accepts additional aa’s.
Reasons for this include the situation where (i) termini of a protein might be
functionally relevant or not accessible [9–11]; (ii) internal fusions might be
Small Functional Peptides and Their Application
in Superfunctionalizing Proteins
Sonja Billerbeck
Columbia University, Department of Chemistry, 550 West 120th Street, New York, NY 10027, USA