Figure 1.

The cell wall of Leptospira spp., a diderm bacteria with inner and outer lipid membranes, is the target for the identification of potential vaccine candidates. The outer leaflet of the outer membrane (OM) is composed of lipopolysaccharide. Lipoproteins can be attached by a lipid anchor to one of the leaflets of either membranes. The IM is spanned by alpha-helix transmembrane proteins while beta-barrel transmembrane proteins span the OM. Leptospiral motility is provided by two flagella that are attached to the IM and are located within the periplasmic space (PS). A peptidoglycan layer is also present in the PS. OM lipoproteins, such as LigA and LigB, as well as OM beta-barrel proteins, such as LptD, BamA, TolC-, TonB-dependent receptors, and other porins have at least a portion of their structure exposed on leptospiral surface and are prospective vaccine candidates, highlighted in gray. The localization of the lipoprotein LipL32 in the OM is controversial; the latest reports indicate that it has a subsurface location (see text).