Evolutionarily divergent Mycobacterium tuberculosis CTP synthase filaments are under selective pressure

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Abstract

The final and rate-limiting enzyme in pyrimidine biosynthesis, CTP synthase (CTPS), is essential for the viability of Mycobacterium tuberculosis and other mycobacteria. Its product, CTP, is critical for RNA, DNA, lipid and cell wall synthesis, and is involved in chromosome segregation. In various organisms across the tree of life, CTPS assembles into higher-order filaments, leading us to hypothesize that M. tuberculosis CTPS (mtCTPS) also forms higher-order structures. Here, we show that mtCTPS does assemble into filaments but with an unusual architecture not seen in other organisms. Through a combination of structural, biochemical, and cellular techniques, we show that polymerization stabilizes the active conformation of the enzyme and resists product inhibition, potentially allowing for the highly localized production of CTP within the cell. Indeed, CTPS filaments localize near the CTP-dependent complex needed for chromosome segregation, and cells expressing mutant enzymes unable to polymerize are altered in their ability to robustly form this complex. Intriguingly, mutants that alter filament formation are under positive selection in clinical isolates of M. tuberculosis , pointing to a critical role needed to withstand pressures imposed by the host and/or antibiotics. Taken together, our data reveal an unexpected mechanism for the spatially organized production of a critical nucleotide in M. tuberculosis , which may represent a vulnerability of the pathogen that can be exploited with chemotherapy.

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  1. This Zenodo record is a permanently preserved version of a PREreview. You can view the complete PREreview at https://prereview.org/reviews/13730150.

    Cytidine triphosphate (CTP) is an essential molecule for all life. The pyrimidine biosynthesis enzyme CTP synthase (CTPS) is known to form filamentous assemblies in numerous diverse lifeforms. This manuscript from Lynch et al reveals new details regarding CTPS in the mycobacteria M. tuberculosis and M. smegmatis. The work identifies a novel filament structure undertaken by CTPS in these species and begins to investigate the functional importance of this structure. 

    The data put forward by the authors presents an exciting new view of this complex system. We have detailed some specific comments below which we feel may improve the strength of this manuscript in its next iteration: 

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