Localization and Functional Characterization of the Alternative Oxidase inNaegleria

Abstract

The Alternative oxidase (AOX) is a protein involved in maintaining the Krebs cycle in instances where the respiratory chain has been inhibited, while allowing for the maintenance of cell growth and necessary metabolic processes for survival. Among eukaryotes, alternative oxidases have disperse distribution and are found in plants, fungi and a few protists, including Naegleria ssp. Naegleria species are free-living unicellular amoeboflagellates, and include the pathogenic species of N. fowleri, the so-called brain eating amoeba. Using a multidisciplinary approach, we aimed to understand the evolution, localization and function of AOX and the role that plays in Naegleria’s biology. Our analyses suggest that the protein was present in last common ancestor of the genus and structure prediction showed that all functional residues are also present in Naegleria species. Using a combination of cellular and biochemical techniques, we also functionally characterize N. gruberi’s AOX in its mitochondria and we demonstrate that its inactivation affects its proliferation. Consequently, we discuss the benefits of the presence of this protein in Naegleria species, along with its potential pathogenicity role in N. fowleri. We predict that our findings will spearhead new explorations to understand the cell biology, metabolism and evolution of Naegleria and other free-living relatives.

Copper Metabolism in Naegleria gruberi and Its Deadly Relative Naegleria fowleri

“…To determine the physiological effect of copper availability on respiration, we performed an oxygen consumption assay with amoebas grown in copper-limited conditions. Both organisms possess two terminal oxidases, cytochrome c oxidase (CCOX) and alternative oxidase (AOX), which couple the electron flow from ubiquinol with the reduction of O 2 to H 2 O ( Cantoni et al, 2020 ). In contrast with CCOX, AOX does not participate in ATP generation.…”