Identification and characterization of a DNA-binding protein from starved cells (Dps) homologue in Acanthamoeba: Implications for encystment-induced DNA protection

Abstract

Acanthamoeba spp. are free-living amoebae recognized as opportunistic human pathogens. Under harsh conditions, trophozoites transform into cysts, undergoing degradation of internal structures and macromolecules, including DNA, which enhances their survival by increasing resistance. However, the mechanism underlying DNA protection in protozoa, such as Acanthamoeba, during the encystment under adverse conditions remains unclear. We cloned a bacterial Dps homologue (AcDps) from Acanthamoeba, then expressed and purified the recombinant AcDps to investigate its functional characteristics. Expression of AcDps is minimal in trophozoites but initiates following encystment induction. When tagged with EGFP, AcDps appears as multiple small vesicle-like structures scattered throughout the cysts' cytoplasm. We examined the factors influencing the formation of rAcDps oligomeric complexes and DNA-rAcDps complexes under various divalent cation and pH conditions by utilizing techniques such as electrophoretic mobility shift assay, and atomic force microscopy imaging. These complexes effectively bind both linear and supercoiled plasmid DNA in the presence of Zn²⁺ divalent cations, creating quasi-DNA complexes that protect the DNA from DNase I degradation. The capacity of rAcDps to oligomerize and bind to DNA, presumed to serve as a protective barrier against damage, highlights its functional and evolutionary importance and suggests its potential as a therapeutic target.