Description:
<jats:p><jats:italic>Borrelia burgdorferi</jats:italic> is the causative agent of Lyme disease and is found in two different types of hosts in nature – <jats:italic>Ixodes</jats:italic> ticks and various mammalian organisms. To initiate disease and survive in mammalian host organisms, <jats:italic>B. burgdorferi</jats:italic> must be able to transfer to a new host, proliferate, attach to different tissue and resist the immune response. To resist the host's immune response, <jats:italic>B. burgdorferi</jats:italic> produces at least five different outer surface proteins that can bind complement regulator factor H (<jats:styled-content style="fixed-case">CFH</jats:styled-content>) and/or factor H‐like protein 1 (<jats:styled-content style="fixed-case">CFHL</jats:styled-content>‐1). The crystal structures of two uniquely folded complement binding proteins, which belong to two distinct gene families and are not found in other bacteria, have been previously described. The crystal structure of the <jats:styled-content style="fixed-case">CFH</jats:styled-content> and <jats:styled-content style="fixed-case">CFHL</jats:styled-content>‐1 binding protein CspZ (also known as Bb<jats:styled-content style="fixed-case">CRASP</jats:styled-content>‐2 or <jats:styled-content style="fixed-case">BBH</jats:styled-content>06) from <jats:italic>B. burgdorferi</jats:italic>, which belongs to a third gene family, is reported in this study. The structure reveals that the overall fold is different from the known structures of the other complement binding proteins in <jats:italic>B. burgdorferi</jats:italic> or other bacteria; this structure does not resemble the fold of any known protein deposited in the Protein Data Bank. The N‐terminal part of the CspZ protein forms a four‐helix bundle and has features similar to the <jats:styled-content style="fixed-case">FAT</jats:styled-content> domain (focal adhesion targeting domain) and a related domain found in the vinculin/α‐catenin family. By combining our findings from the crystal structure of CspZ with previous mutagenesis studies, we have identified a likely binding surface on CspZ for <jats:styled-content style="fixed-case">CFH</jats:styled-content> and <jats:styled-content style="fixed-case">CFHL</jats:styled-content>‐1.</jats:p>