The Helicobacter pylori neutrophil-activating protein is an iron-binding protein with dodecameric structure

The neutrophil-activating protein (HP-NAP) of Helicobacter pylori is a major 17 kDa antigen of the immune response of infected individuals, Amino acid sequence comparison indicated a high similarity between HP-NAP and both bacterial DNA-protecting proteins (Dps) and ferritins, The structure prediction and spectroscopic analysis presented here indicate a close similarity between HP-NAP and ups, Electron microscopy revealed that HP-NAP forms hexagonal rings of 9-10 nm diameter with a hollow central core as seen in Dps proteins, clearly different from the 12 nm icosite-trameric (24 subunits) ferritins, However, HP-NAP is resistant to thermal and chemical denaturation similar to the ferritin family of proteins, In addition, HP-NAP binds up to 40 atoms of iron per monomer and does not bind DNA, We therefore conclude that HP-NAP is an unusual, small, ferritin that folds into a four-helix bundle that oligomerizes into dodecamers with a central hole capable of binding up to 500 iron atoms per oligomer.