Isolation and Characterization of a Putative Hemin-binding Protein from Prevotella intermedia

Abstract

Iron is essential for the growth, reproduction, and survival of all prokaryotic and eukaryotic species1-3). Iron has also been shown to be essential for the initiation and progression of several infectious diseases1). In order to survive therefore, prokaryotes and eukaryotes have devised unique mechanisms to compete for, and sequester the small amounts of iron which are available to them. Eukaryotic cells compete for iron by synthesizing large number of high-affinity iron-binding proteins (i.e., transferrin, lactoferrin), hemoglobin-binding protein (haptoglobin), heme-binding proteins (hemopexin, albumin), and iron-storage proteins (ferritin, hemosiderin) which are capable of competing for, and storing iron1,4-8). Therefore, in order for host-associated bacteria to survive, they must be capable of competing with the host’s large number of highaffinity iron-binding proteins. Prokaryotic cells compete with eukaryotes for this iron by employing two mechanisms: synthesizing their own high-affinity binding and transport proteins, siderophores, and outer membrane associated iron-binding protein. The siderophores are low molecular weight proteins, which bind iron by chelating it from the host, and transferring it to the specific outer membrane receptors which then transport it directly into the cell9). Several Gram-negative bacteria contain, in addition to, or in place of siderophores, iron (hemin) binding proteins in their outer membrane1021). These outer membrane-associated iron-binding proteins are capable of binding iron directly, and transporting it across the outer membrane into the cell. For the most part, these outer membrane expressed iron-binding proteins are expressed during iron stress, and are formed in response to very low levels of iron in the environment. While there are several studies which have dealt with the hemin-binding and hemin-regulated proteins in the oral pathogen, Porphyromonas gingivalis20,22-25), there is no such studies which has studied hemin-binding in Prevotella intermedia. In the study presented here, we have identified, purified, and characterized a putative hemin-binding protein in Prevotella intermedia.