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The J-binding protein 1 (JBP1) is essential for biosynthesis and maintenance of DNA base-J (β-d-glucosyl-hydroxymethyluracil). Base-J and JBP1 are confined to some pathogenic protozoa and are absent from higher eukaryotes, prokaryotes and viruses. We show that JBP1 recognizes J-containing DNA (J-DNA) through a 160-residue domain, DB-JBP1, with 10 000-fold preference over normal DNA. The crystal structure of DB-JBP1 revealed a helix-turn-helix variant fold, a ‘helical bouquet’ with a ‘ribbon’ helix encompassing the amino acids responsible for DNA binding. Mutation of a single residue (Asp525) in the ribbon helix abrogates specificity toward J-DNA. The same mutation renders JBP1 unable to rescue the targeted deletion of endogenous JBP1 genes in Leishmania and changes its distribution in the nucleus. Based on mutational analysis and hydrogen/deuterium-exchange mass-spectrometry data, a model of JBP1 bound to J-DNA was constructed and validated by small-angle X-ray scattering data. Our results open new possibilities for targeted prevention of J-DNA recognition as a therapeutic intervention for parasitic diseases.

We report the discovery and crystal structure of a human mycoplasma protein, Protein M, which binds with high affinity to antibodies, predominantly through attachment to the variable region of the κ and λ light chains. Protein M broadly blocks antibody-antigen union and its mechanism of inhibition is of considerable interest because, as a diversity system, the binding mode of each antibody is different. Protein M thus appears to function by a mechanism that is independent of the sequences of members of the extensive antibody repertoire. By anchoring to conserved regions of the antibody light chains, Protein M is in a position to extend its large C-terminal domain over the antibody combining site and block entrance to macromolecular antigens.

F-18 FDOPA scan is superior to both F-18 FLT and F-18 FDG for visualization of primary and recurrent low grade gliomas. F-18-FLT should not be considered for evaluation of recurrent low grade gliomas.