Successful infection of a host requires that the invading pathogen control its production of virulence determinants. The infectious agent must sense its environment and respond by increasing production of appropriate factors and repressing production of unnecessary ones. These features are especially critical for vector-borne pathogens, which must not only efficiently infect two extremely different host types but also be transmitted back and forth between hosts. Deciphering the regulatory pathways used by pathogens to control production of infection-associated proteins provides significant insight into the infectious nature of those organisms. Moreover, regulatory factors are attractive candidates for development of novel preventative and curative therapies.The spirochetal bacterium Borrelia burgdorferi, the agent of Lyme disease, is an excellent model organism for the study of gene regulation by a vector-borne pathogen. B. burgdorferi is genetically tractable, and its natural mammal-tick infectious cycle can be replicated in the laboratory. In addition, infection by B. burgdorferi is a significant cause of human morbidity, being the most commonly reported vector-borne disease in the United States and many other parts of the world (51, 55, 56).B. burgdorferi Erp lipoproteins are produced throughout mammalian infection but are largely repressed during colonization of vector ticks (10,31,48,49). Erp synthesis is greatly enhanced when B. burgdorferi is transmitted from a feeding tick into a warm-blooded host. Regulation of Erp protein production is controlled at the level of transcription (6). Erp proteins are located in the bacterial outer membrane and are exposed to the external environment (25,32,41). Known functions of Erp proteins include binding of host plasmin(ogen), laminin, and the complement regulators factor H and factor H-related proteins 1, 2, and 5 (2,3,11,12,34,37,40,45,59). These functions indicate roles for Erp proteins in host adherence, dissemination, and resistance to the alternative pathway of complement-mediated killing. Borrelial erp genes are located in mono-or bicistronic operons on extrachromosomal cp32 prophages, most of which replicate autonomously as circular episomes (24,60,63,64,72). Individual Lyme spirochetes naturally contain numerous different cp32 elements, each with a unique erp locus, and therefore produce multiple, distinct Erp surface proteins. A bacterium simultaneously expresses its entire repertoire of Erp proteins (26).A highly conserved DNA region immediately 5= of all erp promoters, the erp operator, is required for regulation of erp transcription (see Fig. 1) (6,10,64). Two erp operator-binding proteins have been identified, and their binding sites have been characterized: BpaB (borrelial plasmid ParB analogue) and EbfC (erp-binding factor, chromosomal) (4, 13, 52). BpaB binds with high affinity to a 5-bp sequence within the erp operator (13; C. A. Adams, unpublished). Binding of one BpaB protein to that sequence then facilitates binding of additional BpaB molecules al...

We developed a single-plasmid-based regulatable protein expression system for Borrelia burgdorferi. Expression of a target gene is driven by P ost , a hybrid B. burgdorferi ospA-tetO promoter, from a recombinant B. burgdorferi plasmid constitutively expressing TetR. The system was tested using the green fluorescent protein (GFP) as a reporter. Under noninducing conditions, recombinant B. burgdorferi cells were nonfluorescent, no GFP protein was detected, and residual, small amounts of transcript were detectable only by reverse transcription-PCR but not by Northern blot hybridization. Upon induction with anhydrotetracycline, increasing levels of GFP transcript, protein, and fluorescence were observed. This tight and titratable promoter system will be invaluable for the study of essential borrelial proteins. Since target protein, operator, and repressor are carried by a single plasmid, the system's application is independent of a particular strain background.

In virtually all eukaryotic cells, protein bridges formed by the conserved inner nuclear membrane SUN (for Sad1-UNC-84) domain-containing proteins and their outer nuclear membrane binding partners span the nuclear envelope (NE) to connect the nucleoplasm and cytoplasm. These linkages are important for chromosome movements within the nucleus during meiotic prophase and are essential for nuclear migration and centrosome attachment to the NE. In Saccharomyces cerevisiae, MPS3 encodes the sole SUN protein. Deletion of MPS3 or the conserved SUN domain is lethal in three different genetic backgrounds. Mutations in the SUN domain result in defects in duplication of the spindle pole body, the yeast centrosome-equivalent organelle. A genome-wide screen for mutants that exhibited synthetic fitness defects in combination with mps3 SUN domain mutants yielded a large number of hits in components of the spindle apparatus and the spindle checkpoint. Mutants in lipid metabolic processes and membrane organization also exacerbated the growth defects of mps3 SUN domain mutants, pointing to a role for Mps3 in nuclear membrane organization. Deletion of SLP1 or YER140W/EMP65 (for ER membrane protein of 65 kDa) aggravated growth of mps3 SUN domain mutants. Slp1 and Emp65 form an ER-membrane associated protein complex that is not required directly for spindle pole body duplication or spindle assembly. Rather, Slp1 is involved in Mps3 localization to the NE.

BackgroundPreviously we reported that the variable outer membrane lipoprotein Vsp1 from the relapsing fever spirochete Borrelia turicatae disseminates from blood to brain better than the closely related Vsp2 [1]. Here we studied the interaction between Vsp1 and Vsp2 with brain endothelium in more detail.Methodology/Principal FindingsWe compared Vsp1 to Vsp2 using human brain microvascular endothelial cell (HBMEC) association assays with aminoacid radiolabeled Vsp-expressing clones of recombinant Borrelia burgdorferi and lanthanide-labeled purified lipidated Vsp1 (LVsp1) and Vsp2 (LVsp2) and inoculations of the lanthanide-labeled proteins into mice. The results showed that heterologous expression of LVsp1 or LVsp2 in B. burgdorferi increased its association with HBMEC to a similar degree. Purified lanthanide-labeled lipidated Vsp1 (LVsp1) and LVsp2 by themselves were capable of associating with HBMEC. The association of LVsp1 with brain endothelium was time-dependent, saturable, and required the lipidation. The association of Vsp1 with HBMEC was inhibited by incubation at lower temperature or with excess unlabeled LVsp1 or LVsp2 but not with excess rVsp1 or mouse albumin or an anti Vsp1 monoclonal antibody. The association of LVsp2 with HBMEC and its movement from blood to brain parenchyma significantly increased in the presence of LVsp1.Conclusions/SignificanceVariable bacterial outer membrane lipoproteins interact with brain endothelium differently; the lipidation and variable features at the protein dome region are key modulators of this interaction.