Extended Structure of Pleiotropic DNA Repair-Promoting Protein PprA from the Extreme Radiation Resistance of Deinococcus radiodurans

Pleiotropic protein promoting DNA repair A (PprA) is a key protein facilitating the extreme radiation resistance of Deinococcus radiodurans. PprA is a 32 kDa protein uniquely found in the genus Deinococcus, and has been identified to exist as an oligomer ranging from tetramer to approximately 100-mer depending on protein concentrations. Here, the X-ray crystal structure of PprA was determined to better understand how PprA confers radiation resistance. The tertiary structure of dimeric PprA was elucidated using mutant W183R obtained by random mutagenesis and subsequently prepared mutant A139R, which exhibits disabled DNA binding and polymerization functions. The crystal structures showed that A139R and W183R mutant proteins have dimeric assemblies with 2 different interfaces (Interfaces 1 and 2). The linear and oligomerized PprA model is constructed as left-handed face-to-face periodic screw structure, where a structural unit is composed of 8 molecules with a pitch of approximately 400 Å. In addition, the linear structure was confirmed by small angle scattering experiments. The site-directed mutational analysis identified indispensable basic amino acids for DNA binding. These analytical data support the hypothesis that a complex assembly of screwed PprA molecules surrounds the broken DNA strands, acting as a novel chaperone to colocalize them for efficient DNA repairs