Biomolecules 2022, 12, 227. https://doi.org/10.3390/biom12020227 www.mdpi.com/journal/biomolecules Review Viral dUTPases: Modulators of Innate Immunity Maria Eugenia Ariza 1,2 , Brandon Cox 2 , Britney Martinez 2 , Irene Mena-Palomo 2 , Gloria Jeronimo Zarate 2 and Marshall Vance Williams 1,2, * 1 Department of Cancer Biology and Genetics, The Ohio State University Wexner Medical Center, Columbus, OH 43210, USA; Maria.Ariza@osumc.edu 2 Institute for Behavioral Medicine Research, The Ohio State University Wexner Medical Center, Columbus, OH 43210, USA; Brandon.Cox@osumc.edu (B.C.); Britney.Martinez@osumc.edu (B.M.); Irene.MenaPalomo@osumc.edu (I.M.-P.); gloriajz881@gmail.com (G.J.Z.) * Correspondence: Marshall.Williams@osumc.edu Abstract: Most free-living organisms encode for a deoxyuridine triphosphate nucleotidohydrolase (dUTPase; EC 3.6.1.23). dUTPases represent a family of metalloenzymes that catalyze the hydrolysis of dUTP to dUMP and pyrophosphate, preventing dUTP from being incorporated into DNA by DNA polymerases, maintaining a low dUTP/dTTP pool ratio and providing a necessary precursor for dTTP biosynthesis. Thus, dUTPases are involved in maintaining genomic integrity by prevent- ing the uracilation of DNA. Many DNA-containing viruses, which infect mammals also encode for a dUTPase. This review will summarize studies demonstrating that, in addition to their classical enzymatic activity, some dUTPases possess novel functions that modulate the host innate immune response. Keywords: deoxyuridine triphosphate nucleotidohydrolase; dUTPase; double-stranded DNA viruses 1. Introduction While there are some exceptions, most free-living organisms encode for a deoxyuri- dine triphosphate nucleotidohydrolase (dUTPase; EC 3.6.1.23) [1]. In addition, many vi- ruses which infect archaea, bacteria, plants and animals also encode for a dUTPase. Stud- ies have demonstrated that the genes encoding for the dUTPases are essential in bacteria [2,3], with the exception of some species [1], yeast [4] and mice [5], suggesting that this enzyme is required for survival/life. This concept is supported by the extensive number of species that possess dUTPases. Pfam, a database of protein families generated on an- notations and sequence alignments using hidden Markov models, has demonstrated the presence of putative dUTPases in at least 8358 species [6]. Data used in this manuscript were collected primarily by Pubmed and pBLAST searches. dUTPases can be divided into at least three structurally distinct families based upon an ordered series of conserved motifs (N-terminal to C-terminal; I, II, III, IV, and V) and structure. The largest family, which exhibits a high specificity for dUTP, is the homotri- meric dUTPases, found in plants, animals, fungi, bacteria and some viruses, including some adenoviruses, poxviruses and retroviruses. These homotrimeric dUTPases, of which prototypes include Escherichia coli and human, are composed of three identical polypep- tides, each folded in an eight-stranded jelly-roll beta barrel and aligned so that the three highly conserved amino acid motifs I, II and IV on one polypeptide interact with the amino acids in conserved motif III of an adjacent peptide. The catalytic site is completed with the binding of dUTP to the flexible C-terminal end of the third polypeptide, which contains the conserved amino acids in motif V. Thus, all three polypeptide subunits con- tribute to the formation of a catalytic site and there are three catalytic sites per holoenzyme [7,8]. Citation: Ariza, M.E.; Cox, B.; Martinez, B.; Mena-Palomo, I.; Zarate, G.J. Williams, M.V. Viral dUTPases: Modulators of Innate Immunity. Biomolecules 2022, 12, 227. https://doi.org/10.3390/ biom12020227 Academic Editor: Judit Toth Received: 1 December 2021 Accepted: 26 January 2022 Published: 28 January 2022 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and institu- tional affiliations. Copyright: © 2022 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https://cre- ativecommons.org/licenses/by/4.0/).