iScience (Jan 2024)

From TgO/GABA-AT, GABA, and T-263 Mutant to Conception of Toxoplasma

  • Joseph Lykins,
  • Matthew J. Moschitto,
  • Ying Zhou,
  • Ekaterina V. Filippova,
  • Hoang V. Le,
  • Tadakimi Tomita,
  • Barbara A. Fox,
  • David J. Bzik,
  • Chunlei Su,
  • Seesandra V. Rajagopala,
  • Kristin Flores,
  • Furio Spano,
  • Stuart Woods,
  • Craig W. Roberts,
  • Cong Hua,
  • Kamal El Bissati,
  • Kelsey M. Wheeler,
  • Sarah Dovgin,
  • Stephen P. Muench,
  • Martin McPhillie,
  • Colin W.G. Fishwick,
  • Wayne F. Anderson,
  • Patricia J. Lee,
  • Mark Hickman,
  • Louis M. Weiss,
  • Jitender P. Dubey,
  • Hernan A. Lorenzi,
  • Richard B. Silverman,
  • Rima L. McLeod

Journal volume & issue
Vol. 27, no. 1
p. 108477

Abstract

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Summary: Toxoplasma gondii causes morbidity, mortality, and disseminates widely via cat sexual stages. Here, we find T. gondii ornithine aminotransferase (OAT) is conserved across phyla. We solve TgO/GABA-AT structures with bound inactivators at 1.55 Å and identify an inactivator selective for TgO/GABA-AT over human OAT and GABA-AT. However, abrogating TgO/GABA-AT genetically does not diminish replication, virulence, cyst-formation, or eliminate cat’s oocyst shedding. Increased sporozoite/merozoite TgO/GABA-AT expression led to our study of a mutagenized clone with oocyst formation blocked, arresting after forming male and female gametes, with “Rosetta stone”-like mutations in genes expressed in merozoites. Mutations are similar to those in organisms from plants to mammals, causing defects in conception and zygote formation, affecting merozoite capacitation, pH/ionicity/sodium-GABA concentrations, drawing attention to cyclic AMP/PKA, and genes enhancing energy or substrate formation in TgO/GABA-AT-related-pathways. These candidates potentially influence merozoite’s capacity to make gametes that fuse to become zygotes, thereby contaminating environments and causing disease.

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