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3 CRISPR Cas: From Bacterial Adaptive Immunity to the Swiss Army Knife of Drug Discovery
Saša Šviković
Genome Engineering, Discovery Sciences, BioPharmaceuticals R&D, AstraZeneca, Gothenburg, Sweden
3.1 Introduction
Over the course of billions of years of evolution, prokaryotes have developed multiple ways to stay ahead of their fiercest foes, mobile genetic elements. These defense systems include a variety of nucleases, DNA‐modifying enzymes, chemical inhibitors, cell death‐inducing signaling pathways, and some not yet fully understood protection systems (Bernheim and Sorek 2020; Hampton et al. 2020). These systems are incredibly diverse and widespread among prokaryotes, and studies into how these systems function ultimately led to the rise of new tools that have revolutionized biomedical sciences. Similarly to how the discovery of an innate bacterial immune system mediated by restriction endonucleases has ushered a revolution in biotechnology (Roberts 2005), the relatively recent discovery of CRISPR‐Cas systems, an adaptive immune component of prokaryotic defense systems, and their application in genome engineering has completely changed the way how research in life sciences is done. In this Chapter, we will address the basics of CRISPR biology, the diversity and current classification schemes, and how the mechanistic understanding of these diverse systems can give rise to novel tools for biomedical science.
3.2 CRISPR Biology in a Nutshell
CRISPR, or Clustered Regularly Interspaced Short Palindromic Repeats, represents an adaptive immune system of microbes, able to adapt in response to invasions by mobile genetic elements such as bacteriophages, plasmids, and transposons. The locus encoding for the components of the CRISPR system was discovered as an array of palindromic repeats interrupted by a 20–40 nt sequence downstream of the iap gene in Escherichia coli (Ishino et al. 1987; Nakata et al. 1989). Thanks to the increasing availability of sequences from the microbial species, the structure of CRISPR loci, with many properties relating to
