Complement Immune Evasion by Spirochetes.

The complement system plays an important role in the innate and acquired immune response against pathogens. A sophisticated network of activating and regulating proteins allows the distinction between intact and damaged host and non-host surfaces such as bacteria and other parasites. Non-host structures trigger the alternative pathway which may lead to their elimination by phagocytosis or cell lysis. In addition, complement proteins such as C1q, mannose binding lectin (MBL), and ficolins act as pathogen pattern-recognition molecules. Biological functions such as opsonization, activation of B lymphocytes and production of antibodies, degranulation of mast cells and basophils, and cell lysis that are important for elimination of microorganisms are dependent on complement activation. However, several pathogens including spirochetes have developed several specialized mechanisms to evade the complement system, thereby contributing to survival in the host. In this review, we give a brief overview of complement activation and regulation, and discuss in detail the strategies used by spirochetes from the genera Borrelia, Leptospira, and Treponema to overcome complement activation.

The crystal structure of the leptospiral hypothetical protein LIC12922 reveals homology with the periplasmic chaperone SurA

Leptospirosis is a world spread zoonosis caused by members of the genus Leptospira. Although leptospireswere identified as the causal agent of leptospirosis almost 100 years ago, little is known about their biology,which hinders the development of new treatment and prevention strategies. One of the severalaspects of the leptospiral biology not yet elucidated is the process by which outer membrane proteins (OMPs) traverse the periplasm and are inserted into the outer membrane. The crystal structure determination of the conserved hypothetical protein LIC12922 from Leptospira interrogans revealed a two domain protein homologous to the Escherichia coli periplasmic chaperone SurA. The LIC12922 NC-domain isstructurally related to the chaperone modules of E. coli SurA and trigger factor, whereas the parvulindomain is devoid of peptidyl prolyl cis–trans isomerase activity. Phylogenetic analyses suggest a relationshipbetween LIC12922 and the chaperones PrsA, PpiD and SurA. Based on our structural and evolutionaryanalyses, we postulate that LIC12922 is a periplasmic chaperone involved in OMPs biogenesis inLeptospira spp. Since LIC12922 homologs were identified in all spirochetal genomes sequenced to date,this assumption may have implications for the OMPs biogenesis studies not only in leptospires but in the entire Phylum Spirochaetes.