6.4. AMYLOIDOGENIC PROTEINS ARE INTEGRAL PART OF BACTERIA (SPIROCHETES)

As the spirochetes Borrelia burgdorferi and Treponema pallidum showed immunoreactivity for APP (Miklossy 1993, 1994a) as analyzed by immunohistochemistry and immunelectron microscopy, we have suggested that amyloidogenic proteins may be an integral part of spirochetes and play a role in amyloidogenesis in AD. That Borrelia burgdorferi contains amyloidogenic protein was later reinforced by Ohnishi et al., (2000, 2001) who showed that the BH (9-10) peptide of the beta/hairpin segment of the Outer surface protein A (OspA) is amyloidogenic and forms amyloid fibrils similar to human amyloid in vitro.

Indeed, recent observations indicate that amyloid peptides or proteins constitute a previously overlooked integral part of the cellular envelope of many bacteria (Chapman et al., 2002; Otzen and Nielsen 2008; Jordal et al., 2009). Amyloid fibril formation not only results in toxic aggregates, but provides biologically functional molecules (Chapman et al., 2002; Otzen and Nielsen 2008; Wang et al., 2008). Bacterial amyloids are involved in bacterial cell-cell interactions, in their attachment to inert solid surfaces, and in spore and biofilm formation (Wang et al., 2008). Microbial amyloids, through interaction with host proteases also contribute to bacterial virulence, to colonization of the host and to invasion of host cells.