Barnase-Barstar Pair: Contemporary Application in Cancer Research and Nanotechnology

Abstract

Barnase is an extracellular ribonuclease secreted by Bacillus amyloliquefaciens that was originally studied as a small stable enzyme with robust folding. The identification of barnase intracellular inhibitor barstar led to the discovery of an incredibly strong protein-protein interaction. Together, barnase and barstar provide a fully genetically encoded toxin-antitoxin pair having an extremely low dissociation constant. Moreover, compared to other dimerization systems, the barnase-barstar module provides the exact one-to-one ratio of the complex components and possesses high stability of each component in a complex and high solubility in aqueous solutions without self-aggregation. The unique properties of barnase and barstar allow the application of this pair for the engineering of different variants of targeted anticancer compounds and cytotoxic supramolecular complexes. Using barnase in suicide gene therapy has also found its niche in anticancer therapy. The application of barnase and barstar in contemporary experimental cancer therapy is reflected in the review.

Targeted Delivery of HSP70 to Tumor Cells via Supramolecular Complex Based on HER2-Specific DARPin9_29 and the Barnase:Barstar Pair

“…The selective interaction between the first and second modules is facilitated by the uniquely high binding constant of barstar to barnase; this protein heterodimer forms a complex with a K D ~10 −14 M, comparable only to the streptavidin-biotin system (K D ~10 −14 M). Our studies demonstrated the effectiveness of the barnase:barstar complex for the delivery of various drugs to cancer cells [2,3,19].…”

Prospects of Using Protein Engineering for Selective Drug Delivery into a Specific Compartment of Target Cells

“…An example of this kind of artificial molecule is modular nanotransporters that combine several transport functions: binding to the receptor and endocytosis, endosome escape and transport into the cell nucleus [ 45 , 46 , 68 , 149 , 150 , 153 , 154 , 155 , 156 , 157 , 193 , 224 ]. Those artificial protein molecules combining several polypeptide moieties can be either produced by genetic engineering or by various post-translational protein assembly approaches (e.g., barnase-barstar-based [ 288 ], enzymatic-mediated protein ligation [ 289 , 290 ], intein-mediated ligation [ 290 , 291 ], and SpyTag/SpyCatcher [ 292 ]). The delivery of cytotoxic agents to the most vulnerable cellular compartments is the most obvious opportunity for cancer treatment.…”

Targeting Ribonucleases with Small Molecules and Bifunctional Molecules

“…Covalent inhibitors binding to the ribonuclease or adjacent domains were reported for IRE1. Reported covalent compounds showed improved efficiency in targeting shallow binding sites and thus hold great potential for developing potent RNase-targeting small molecules. ,− Of note, cytotoxic RNases such as Ranpirnase and Barnase have also been studied for their direct use as anticancer agents in gene therapy. , A new perspective in the field is the emerging class of bifunctional molecules that target RNases Dicer and RNase L for specific inhibition or activation of the RNases, achieving either inhibition of RNA biogenesis or induced RNA degradation. Concerning the biological relevance of RNases and their close associations with pathological states, it is reasonable to expect that more RNases will be subject both as the protein targets of interest for bifunctional molecules and as the effector protein components to be utilized by bifunctional molecules.…”