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 Dps. 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 icositetrameric (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.
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Document Type: Research Article
Centro CNR Biomembrane and Dipartimento di Scienze Biomediche, Università di Padova, I-35121, Italy.,
Laboratory for Biochemistry, Swiss Federal Institute of Technology, Zurich, Switzerland.,
Centro CNR per la Fisiologia e Biochimica delle Metalloproteine, Dipartimento di Biologia, Università di Padova, I-35121, Italy.,
IRIS/CHIRON S.p.A., Via Fiorentina 1, Siena, Italy.
October 1, 1999