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Crystal structure of an iron superoxide dismutase from the pathogenic amoeba Acanthamoeba castellanii.

ABSTRACT: The iron superoxide dismutase found in the pathogenic amoeba Acanthamoeba castellanii (AcFeSOD) may play essential roles in the survival of the parasite, not only by protecting it from endogenous oxidative stress but also by detoxifying oxidative killing of the parasite by host immune effector cells. The AcFeSOD protein was expressed in a stable form using an Escherichia coli expression system and was crystallized by the microbatch and hanging-drop vapour-diffusion methods. The structure was determined to 2.33?Å resolution from a single AcFeSOD crystal. The crystal belonged to the hexagonal space group P61 and contained 12 molecules forming three tetramers in the asymmetric unit, with an iron ion bound in each molecule. Structural comparisons and sequence alignment of AcFeSOD with other FeSODs showed a well conserved overall fold and conserved active-site residues with subtle differences.

SUBMITTER: Dao O

PROVIDER: S-EPMC6613442 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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Crystal structure of an iron superoxide dismutase from the pathogenic amoeba Acanthamoeba castellanii.

Dao Oanh O Asaithambi Killivalavan K Na Byeong Kuk BK Lee Kon Ho KH

Acta crystallographica. Section F, Structural biology communications 20190626 Pt 7

The iron superoxide dismutase found in the pathogenic amoeba Acanthamoeba castellanii (AcFeSOD) may play essential roles in the survival of the parasite, not only by protecting it from endogenous oxidative stress but also by detoxifying oxidative killing of the parasite by host immune effector cells. The AcFeSOD protein was expressed in a stable form using an Escherichia coli expression system and was crystallized by the microbatch and hanging-drop vapour-diffusion methods. The structure was det ...[more]

PMID: 31282867

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Project description:In this study, we conducted an in-depth analysis to characterize potential Acanthamoeba castellanii (Ac) proteins capable of recognizing fungal β-1,3-glucans. Ac specifically anchors curdlan or laminarin, indicating the presence of surface β-1,3-glucan-binding molecules. Using optical tweezers, strong adhesion of laminarin- or curdlan-coated beads to Ac was observed, highlighting their adhesive properties compared to controls (characteristic time τ of 46.9 and 43.9 s, respectively). Furthermore, Histoplasma capsulatum (Hc) G217B, possessing a β-1,3-glucan outer layer, showed significant adhesion to Ac compared to a Hc G186 strain with an α-1,3-glucan outer layer (τ of 5.3 s vs τ 83.6 s). The addition of soluble β-1,3-glucan substantially inhibited this adhesion, indicating the involvement of β-1,3-glucan recognition. Biotinylated β-1,3-glucan-binding proteins from Ac exhibited higher binding to Hc G217B, suggesting distinct recognition mechanisms for laminarin and curdlan, akin to macrophages. These observations hinted at the β-1,3-glucan recognition pathway's role in fungal entrance and survival within phagocytes, supported by decreased fungal viability upon laminarin or curdlan addition in both phagocytes. Proteomic analysis identified several Ac proteins capable of binding β-1,3-glucans, including those with lectin/glucanase superfamily domains, carbohydrate-binding domains, and glycosyl transferase and glycosyl hydrolase domains. Notably, some identified proteins were overexpressed upon curdlan/laminarin challenge and also demonstrated high affinity to β-1,3-glucans. These findings underscore the complexity of binding via β-1,3-glucan and suggest the existence of alternative fungal recognition pathways in Ac.IMPORTANCEAcanthamoeba castellanii (Ac) and macrophages both exhibit the remarkable ability to phagocytose various extracellular microorganisms in their respective environments. While substantial knowledge exists on this phenomenon for macrophages, the understanding of Ac's phagocytic mechanisms remains elusive. Recently, our group identified mannose-binding receptors on the surface of Ac that exhibit the capacity to bind/recognize fungi. However, the process was not entirely inhibited by soluble mannose, suggesting the possibility of other interactions. Herein, we describe the mechanism of β-1,3-glucan binding by A. castellanii and its role in fungal phagocytosis and survival within trophozoites, also using macrophages as a model for comparison, as they possess a well-established mechanism involving the Dectin-1 receptor for β-1,3-glucan recognition. These shed light on a potential parallel evolution of pathways involved in the recognition of fungal surface polysaccharides.

Dataset Information

Crystal structure of an iron superoxide dismutase from the pathogenic amoeba Acanthamoeba castellanii.

Publications

Crystal structure of an iron superoxide dismutase from the pathogenic amoeba Acanthamoeba castellanii.

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