Global mapping of the Chlamydia trachomatis conventional secreted effector - host interactome reveals CebN interacts with nucleoporins and Rae1 to impede STAT1 nuclear translocation

Chlamydia trachomatis ( C.t .), the leading cause of bacterial sexually transmitted infections, employs a type III secretion system (T3SS) to translocate two classes of effectors, inclusion membrane proteins and conventional T3SS (cT3SS) effectors, into the host cell to counter host defense mechanisms. Here we employed three assays to directly evaluate secretion during infection, validating secretion for 23 cT3SS effectors. As bioinformatic analyses have been largely unrevealing, we conducted affinity purification-mass spectrometry to identify host targets and gain insights into the functions of these effectors, identifying high confidence interacting partners for 21 cT3SS effectors. We demonstrate that CebN localizes to the nuclear envelope in infected and bystander cells where it interacts with multiple nucleoporins and Rae1, blocking STAT1 nuclear import following IFN-γ stimulation. By building a cT3SS effector-host interactome, we have identified novel pathways that are targeted during bacterial infection and have begun to address how C.t. effectors combat cell autonomous immunity.

Identification and Preliminary Characterization of Novel Type III Secreted Effector Proteins in Chlamydia trachomatis

Chlamydia trachomatis is an obligate intracellular pathogen that replicates in a host-derived vacuole termed the inclusion. Central to pathogenesis is a type III secretion system that translocates effector proteins into the host cell, which are predicted to play major roles in host cell invasion, nutrient acquisition, and immune evasion. However, until recently, the genetic intractability of C. trachomatis hindered identification and characterization of these important virulence factors. Here, we sought to expand the repertoire of identified effector proteins and confirm they are secreted during C. trachomatis infection. Utilizing bioinformatics, we identified 18 candidate substrates that had not been previously assessed for secretion, of which we show four to be secreted, using Yersinia pseudotuberculosis as a surrogate host. Using adenylate cyclase (CyaA), BlaM, and glycogen synthase kinase (GSK) secretion assays, we identified nine novel substrates that were secreted in at least one assay. Interestingly, only three of the substrates, shown to be translocated by C. trachomatis, were similarly secreted by Y. pseudotuberculosis. Using large-scale screens to determine subcellular localization and identify effectors that perturb crucial host cell processes, we identified one novel substrate, CT392, that is toxic when heterologously expressed in Saccharomyces cerevisiae. Toxicity required both the N- and C-terminal regions of the protein. Additionally, we show that these newly described substrates traffic to distinct host cell compartments, including vesicles and the cytoplasm. Collectively, our study expands the known repertoire of C. trachomatis secreted factors and highlights the importance of testing for secretion in the native host using multiple secretion assays when possible.

The Chlamydia trachomatis type III-secreted effector protein CteG induces centrosome amplification through interactions with centrin-2

The centrosome is the main microtubule organizing center of the cell and is crucial for mitotic spindle assembly, chromosome segregation, and cell division. Centrosome duplication is tightly controlled, yet several pathogens, most notably oncogenic viruses, perturb this process leading to increased centrosome numbers. Infection by the obligate intracellular bacterium Chlamydia trachomatis (C.t.) correlates with blocked cytokinesis, supernumerary centrosomes, and multipolar spindles; however, the mechanisms behind how C.t. induces these cellular abnormalities remain largely unknown. Here we show that the secreted effector protein, CteG, binds to centrin-2 (CETN2), a key structural component of centrosomes and regulator of centriole duplication. Our data indicate that both CteG and CETN2 are necessary for infection-induced centrosome amplification, in a manner that requires the C-terminus of CteG. Strikingly, CteG is important for in vivo infection and growth in primary cervical cells but is dispensable for growth in immortalized cells, highlighting the importance of this effector protein to chlamydial infection. These findings begin to provide mechanistic insight into how C.t. induces cellular abnormalities during infection, but also indicate that obligate intracellular bacteria may contribute to cellular transformation events. Centrosome amplification mediated by CteG-CETN2 interactions may explain why chlamydial infection leads to an increased risk of cervical or ovarian cancer.

Using a competitive counterflow assay to identify novel cationic substrates of OATP1B1 and OATP1B3

OATP1B1 and OATP1B3 are two drug transporters that mediate the uptake of multiple endo- and xenobiotics, including many drugs, into human hepatocytes. Numerous inhibitors have been identified, and for some of them, it is not clear whether they are also substrates. Historically radiolabeled substrates or LC-MS/MS methods were needed to test for transported substrates, both of which can be limiting in time and money. However, the competitive counterflow (CCF) assay originally described for OCT2 and, more recently, for OCT1, OATP2B1, and OATP1A2 does not require radiolabeled substrates or LC-MS/MS methods and, as a result, is a more cost-effective approach to identifying substrates of multidrug transporters. We used a CCF assay based on the stimulated efflux of the common model substrate estradiol-17β-glucuronide (E17βG) and tested 30 compounds for OATP1B1- and OATP1B3-mediated transport. Chinese Hamster Ovary (CHO) cells stably expressing OATP1B1 or OATP1B3 were preloaded with 10 nM [³H]-estradiol-17β-glucuronide. After the addition of known substrates like unlabeled estradiol-17β-glucuronide, estrone-3-sulfate, bromosulfophthalein, protoporphyrin X, rifampicin, and taurocholate to the outside of the preloaded CHO cells, we observed efflux of [³H]-estradiol-17β-glucuronide due to exchange with the added compounds. Of the tested 30 compounds, some organic cation transporter substrates like diphenhydramine, metformin, and salbutamol did not induce [³H]-estradiol-17β-glucuronide efflux, indicating that the two OATPs do not transport them. However, 22 (for OATP1B1) and 16 (for OATP1B3) of the tested compounds resulted in [³H]-estradiol-17β-glucuronide efflux, suggesting that they are OATP substrates. Among these compounds, we further tested clarithromycin, indomethacin, reserpine, and verapamil and confirmed that they are substrates of the two OATPs. These results demonstrate that the substrate spectrum of the well-characterized organic anion transporting polypeptides includes several organic cations. Furthermore, as for other drug uptake transporters, the CCF assay is an easy-to-use screening tool to identify novel OATP substrates.

Got mutants? How advances in chlamydial genetics have furthered the study of effector proteins

Chlamydia trachomatis is the leading cause of infectious blindness and a sexually transmitted infection. All chlamydiae are obligate intracellular bacteria that replicate within a membrane-bound vacuole termed the inclusion. From the confines of the inclusion, the bacteria must interact with many host organelles to acquire key nutrients necessary for replication, all while promoting host cell viability and subverting host defense mechanisms. To achieve these feats, C. trachomatis delivers an arsenal of virulence factors into the eukaryotic cell via a type 3 secretion system (T3SS) that facilitates invasion, manipulation of host vesicular trafficking, subversion of host defense mechanisms and promotes bacteria egress at the conclusion of the developmental cycle. A subset of these proteins intercalate into the inclusion and are thus referred to as inclusion membrane proteins. Whereas others, referred to as conventional T3SS effectors, are released into the host cell where they localize to various eukaryotic organelles or remain in the cytosol. Here, we discuss the functions of T3SS effector proteins with a focus on how advances in chlamydial genetics have facilitated the identification and molecular characterization of these important factors.

Gly45 and Phe555 in Transmembrane Domains 1 and 10 Are Critical for the Activation of Organic Anion Transporting Polypeptide 1B3 by Epigallocatechin Gallate

Organic anion transporting polypeptides (OATPs) 1B1 and 1B3 are two highly homologous transporters expressed in the human liver. However, epigallocatechin gallate (EGCG), which is the most predominant catechin in green tea, has opposite effects on the function of OATP1B1 and OATP1B3. In the present study, the critical structural domains and amino acid residues for the activation of OATP1B3 by EGCG have been determined by characterizing the function of a series of OATP1B3-derived chimeric transporters, site-directed mutagenesis, and kinetic studies. Our results showed that G45 and F555 in transmembrane domains 1 and 10 are the most important amino acid residues for OATP1B3 activation. Kinetic studies showed that the activation of OATP1B3 by EGCG at a low substrate concentration was due to its increased substrate binding affinity. However, EGCG caused increased K_m and decreased V_max for 1B3-G45A and 1B3-F555H. The flexibility at position 45 and aromaticity at position 555 might be important for OATP1B3 activation. While 1B3-G45A and 1B3-F555H could not be activated by EGCG, their transport activity for EGCG was comparable to that of wild-type OATP1B3. In conclusion, the present study elucidated the molecular mechanism for OATP1B3 activation by EGCG.

Data2Dynamics: a modeling environment tailored to parameter estimation in dynamical systems

Modeling of dynamical systems using ordinary differential equations is a popular approach in the field of systems biology. Two of the most critical steps in this approach are to construct dynamical models of biochemical reaction networks for large datasets and complex experimental conditions and to perform efficient and reliable parameter estimation for model fitting. We present a modeling environment for MATLAB that pioneers these challenges. The numerically expensive parts of the calculations such as the solving of the differential equations and of the associated sensitivity system are parallelized and automatically compiled into efficient C code. A variety of parameter estimation algorithms as well as frequentist and Bayesian methods for uncertainty analysis have been implemented and used on a range of applications that lead to publications.

AVAILABILITY AND IMPLEMENTATION

The Data2Dynamics modeling environment is MATLAB based, open source and freely available at http://www.data2dynamics.org.

CONTACT

andreas.raue@fdm.uni-freiburg.de

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Bioavailability of zinc from zinc-histidine complexes. I. Comparison with zinc sulfate in healthy men

Zinc supplementation is beneficial in some clinical conditions. Histidine has been shown to improve zinc absorption in animals. To test its influence on zinc absorption in humans, we studied the bioavailability of zinc from zinc-histidine complexes as compared to zinc sulfate in 10 healthy volunteers. Ingestion of zinc complexed with histidine at a ratio of 1:2 or 1:12 increased serum-zinc concentration 25% more than ingestion of zinc sulfate. Calculated uptake was 30-40% increased with zinc histidine over zinc sulfate. Urinary excretion was not different with any preparation. Application of 15 mg zinc as zinc histidine 1:2 gave an identical serum-zinc response as 45 mg zinc taken as zinc sulfate. Zinc histidine complexes are better absorbed than zinc sulfate in humans.