From Tg O/GABA-AT, GABA, and T-263 Mutant to Conception of Toxoplasma .

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 Tg O/GABA-AT structures with bound inactivators at 1.55 Å and identify an inactivator selective for Tg O/GABA-AT over human OAT and GABA-AT. However, abrogating Tg O/GABA-AT genetically does not diminish replication, virulence, cyst-formation, or eliminate cat's oocyst shedding. Increased sporozoite/merozoite Tg O/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 Tg O/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.
Competing Interests: H.V.L. is currently a program officer at the National Institute on Drug Abuse at the National Institutes of Health. H.A.L. is currently a scientist working at National Institute of Diabetes, Digestive and Kidney Disease (NIDDK) at the National Institutes of Health. The findings and conclusions of this article are those of the authors and do not necessarily reflect the views of the National Institute on Drug Abuse, National Institute of Diabetes, Digestive and Kidney Diseases (NIDDK), the National Institutes of Health, nor the US Department of Health and Human Services. R.B.S. and R.L.M., with H.V.L., submitted Patent Number: US 10,632,088 B2 INACTIVATORS OF TOXOPLASMA GONDII ORNITHINE AMINOTRANSFERASE FOR TREATING TOXOPLASMOSIS AND MALARIA through their Technology Transfer offices. The authors declare no competing financial interest.
(© 2023 The Authors.)