HP0268 is a small, characterized protein that is conserved in H. pylori strains and consists of 80 amino acid residues with a molecular weight of approximately 9.5 kDa. HP0268 has nicking endonuclease and RNase activities, both of which are specific for a single-strand of nucleotides. It is structurally similar to small MutS-related (SMR) domains, that can be categorized roughly into three subfamilies according to their arrangement in the domain architecture.HP0268 falls into subfamily 3 that is found as stand-alone type proteins. It is proposed that HP0268 has become an evolutionary intermediate between RNases and nicking endonucleases during H. pylori adaptation to the extremely acidic environment of the stomach [1].

1: Structure-based functional identification of Helicobacter pylori HP0268 as a nuclease with both DNA nicking and RNase activities. Lee KY, Lee KY, Kim JH, Lee IG, Lee SH, Sim DW, Won HS, Lee BJ; Nucleic Acids Res. 2015;43:5194-5207. PMID:25916841