Nucleases and Their Inhibitors: Exploring Biological Roles, Industrial Applications, and Challenges in Heterologous Expression

Nucleases hydrolyze phosphodiester bonds and participate in numerous cellular and metabolic processes. Intracellular nucleases repair nonfunctional or damaged DNA using DNA base excision repair (BER), mismatch repair (MMR), and homologous recombination (HR). Apoptotic nucleases systematically degrade cellular DNA during programmed cell death (PCD). Non-apoptotic nucleases support DNA repair and replication. Small noncoding RNAs (sncRNAs) degrade the RNA of viral particles. Extracellular and membrane-associated nucleases replenish nucleotides, especially in biofilms where cells rely on additional carbon, phosphorus, and energy. Restriction endonucleases (REs) are indispensable in recombinant DNA technology. Some genetic disorders and cancers have been treated by changing the genetic code of host cells using the CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR-associated proteins) system. Nucleases are also used in vaccine development. Heterologous expression of nucleases remains challenging, largely due to cytotoxicity and product instability. Some successes have been reported using the T7 promoter-based system. However, due to the formation of inclusion bodies (IBs), the nucleases were insoluble and of low activity. Refolding misfolded nucleases from IBs, tight control (sequestration) of periplasmic secretion, and coexpression with natural inhibitor proteins increased yield, purity, and biological activity. This review addresses the significance of nucleases, heterologous expression, gene regulation, activity inhibition, and product yield.