Biotechnology and Bioprocess Engineering 2019; 24(5): 702-712  
Stabilization of Proteins by Covalent Cyclization
Anwesha Purkayastha and Taek Jin Kang*
Department of Chemical and Biochemical Engineering, Dongguk University-Seoul, Seoul 04620, Korea
Correspondence to: Taek Jin Kang
Department of Chemical and Biochemical Engineering, Dongguk University-Seoul, Seoul 04620, Korea
Tel: +82-2-2260-3363; Fax: +82-2-2260-3363
E-mail: taekkang@dongguk.edu
Received: September 21, 2019; Revised: September 29, 2019; Accepted: September 29, 2019; Published online: October 31, 2019.
© The Korean Society for Biotechnology and Bioengineering. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Stabilizing proteins against the thermal stress or proteolytic attacks is an important goal in many protein engineering studies. As the simplest approach to the rational engineering of proteins, cyclizing proteins covalently has attracted a great deal of attention. The idea of stabilizing the folded state of a protein by connecting its loose ends came from the polymer theory and was evidenced by many super-stable cyclic peptides/proteins present in nature. Laboratory methodologies utilizing various tools such as inteins, transpeptidases, transglutaminases and split cellular anchoring proteins have been developed, engineered, and successfully adopted to protein cyclization reactions. Depending on the method used, N- and C-termini could be joined together to yield backbone cyclized proteins, or side chains located near the ends might be crosslinked to yield side chain cyclized ones. As each of the methods has its own pros and cons in its reaction scheme, the outcomes such as an increase in melting temperature of a given protein are different when different methods are applied. In this review, we highlight the stabilizing effects exerted by protein cyclization focusing on not a specific cyclizing method but product proteins.
Keywords: protein cyclization, protein stabilization, intein, sortase, butelase-1, SpyTag


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