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Abstract: Babesia divergens is the Apicomplexa agent of the bovine babesiosis in Europe: this infection leads to growth and lactation decrease, so that economical losses due to this parasite are sufficient to require the development of a vaccine. The major surface antigen of B. divergens has been described as a 37 kDa protein glycosyl phosphatidyl inositol (GPI)-anchored at the surface of the merozoite. The immuno-prophylactic potential of Bd37 has been demonstrated, and we present here the high-resolution solution structure of the 27 kDa structured core of Bd37 (Δ-Bd37) using NMR spectroscopy. A model for the whole protein has been obtained using additional small angle X-ray scattering (SAXS) data. The knowledge of the 3D structure of Bd37 allowed the precise epitope mapping of antibodies on its surface. Interestingly, the geometry of Δ-Bd37 reveals an intriguing similarity with the exocyst subunit Exo84p C-terminal region, an eukaryotic protein that has a direct implication in vesicle trafficking. This strongly suggests that Apicomplexa have developed in parallel molecular machines similar in structure and function to the ones used for endo- and exocytosis in eukaryotic cells. [Copyright &y& Elsevier]

[Display omitted] • The G4 helicase BsPif1 possesses independent binding sites for both ssDNA and G4. • ssDNA translocation driven by ATP hydrolysis, exerts a pulling force on G4 unwinding. • There is a distinct G4 binding region that play a critical role in G4 unwinding. • A novel theoretical framework for the G4 development mechanism within Pif1 helicases. The G-quadruplex (G4) is a distinct geometric and electrophysical structure compared to classical double-stranded DNA, and its stability can impede essential cellular processes such as replication, transcription, and translation. This study focuses on the Bs Pif1 helicase, revealing its ability to bind independently to both single-stranded DNA (ssDNA) and G4 structures. The unfolding activity of Bs Pif1 on G4 relies on the presence of a single tail chain, and the covalent continuity between the single tail chain and the G4′s main chain is necessary for efficient G4 unwinding. This suggests that ATP hydrolysis-driven ssDNA translocation exerts a pull force on G4 unwinding. Molecular dynamics simulations identified a specific region within Bs Pif1 that contains five crucial amino acid sites responsible for G4 binding and unwinding. A "molecular wire stripper" model is proposed to explain Bs Pif1′s mechanism of G4 unwinding. These findings provide a new theoretical foundation for further exploration of the G4 development mechanism in Pif1 family helicases. [ABSTRACT FROM AUTHOR]