Iron-repressible outer membrane proteins of Helicobacter pylori involved in heme uptake

Helicobacter pylori is known to be a causative agent of gastritis and peptic ulcer disease in humans. The acquisition of iron from the human host may contribute greatly to the virulence of this organism. To study this, H. pylori was cultured under iron-restrictive conditions to induce synthesis of possible iron-regulated outer membrane proteins. This was achieved by the addition of 20% (vol/vol) heat-inactivated newborn calf serum, which contains iron-binding proteins like transferrin and albumin, and no free iron. The newborn calf serum was able to bind free ionic iron in brucella broth culture medium. Electrophoretic analysis of outer membrane preparations from H. pylori cultured under conditions of iron restriction showed several proteins to be present at elevated levels. These appeared to be iron-repressible outer membrane proteins (IROMPs). In addition, IROMPs with molecular sizes of 77, 50, and 48 kDa were isolated by use of hemin-agarose affinity chromatography. These three heme-binding IROMPs might be involved in the uptake of heme from the host and might therefore be important virulence factors of H. pylori.