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 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.
Tonello
F
F
Centro CNR Biomembrane and Dipartimento di Scienze Biomediche, Università di Padova, I-35121, Italy.
Dundon
W G
WG
Satin
B
B
Molinari
M
M
Tognon
G
G
Grandi
G
G
Del Giudice
G
G
Rappuoli
R
R
Montecucco
C
C
D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D002942:Circular Dichroism; D004247:DNA / Q000378:metabolism; D016480:Helicobacter pylori / Q000737:chemistry* / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D008854:Microscopy, Electron; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011489:Protein Denaturation; D013050:Spectrometry, Fluorescence
D001426:Bacterial Proteins; C092412:neutrophil-activating protein A, Helicobacter pylori; D004247:DNA; D007501:Iron