Soluble Frizzled-related proteins promote exosome-mediated Wnt re-secretion

Wnt proteins are thought to be transported in several ways in the extracellular space. For instance, they are known to be carried by exosomes and by Wnt-carrier proteins, such as sFRP proteins. However, little is known about whether and/or how these two transport systems are related. Here, we show that adding sFRP1 or sFRP2, but not sFRP3 or sFRP4, to culture medium containing Wnt3a or Wnt5a increases re-secretion of exosome-loaded Wnt proteins from cells. This effect of sFRP2 is counteracted by heparinase, which removes sugar chains on heparan sulfate proteoglycans (HSPGs), but is independent of LRP5/6, Wnt co-receptors essential for Wnt signaling. Wnt3a and Wnt5a specifically dimerize with sFRP2 in culture supernatant. Furthermore, a Wnt3a mutant defective in heterodimerization with sFRP2 impairs the ability to increase exosome-mediated Wnt3a re-secretion. Based on these results, we propose that Wnt heterodimerization with its carrier protein, sFRP2, enhances Wnt accumulation at sugar chains on HSPGs on the cell surface, leading to increased endocytosis and exosome-mediated Wnt re-secretion. Our results suggest that the range of action of Wnt ligands is controlled by coordination of different transport systems.

Amyloid conformation-dependent disaggregation in a reconstituted yeast prion system

Disaggregation of amyloid fibrils is a fundamental biological process required for amyloid propagation. However, due to the lack of experimental systems, the molecular mechanism of how amyloid is disaggregated by cellular factors remains poorly understood. Here, we established a robust in vitro reconstituted system of yeast prion propagation and found that heat-shock protein 104 (Hsp104), Ssa1 and Sis1 chaperones are essential for efficient disaggregation of Sup35 amyloid. Real-time imaging of single-molecule fluorescence coupled with the reconstitution system revealed that amyloid disaggregation is achieved by ordered, timely binding of the chaperones to amyloid. Remarkably, we uncovered two distinct prion strain conformation-dependent modes of disaggregation, fragmentation and dissolution. We characterized distinct chaperone dynamics in each mode and found that transient, repeated binding of Hsp104 to the same site of amyloid results in fragmentation. These findings provide a physical foundation for otherwise puzzling in vivo observations and for therapeutic development for amyloid-associated neurodegenerative diseases.

Sedimentation velocity analytical ultracentrifugation for characterization of therapeutic antibodies

Sedimentation velocity analytical ultracentrifugation (SV-AUC) coupled with direct computational fitting of the observed concentration profiles (sedimentating boundary) have been developed and widely used for the characterization of macromolecules and nanoparticles in solution. In particular, size distribution analysis by SV-AUC has become a reliable and essential approach for the characterization of biopharmaceuticals including therapeutic antibodies. In this review, we describe the importance and advantages of SV-AUC for studying biopharmaceuticals, with an emphasis on strategies for sample preparation, data acquisition, and data analysis. Recent discoveries enabled by AUC with a fluorescence detection system and potential future applications are also discussed.

Analytical ultracentrifugation with fluorescence detection system reveals differences in complex formation between recombinant human TNF and different biological TNF antagonists in various environments

A number of studies have attempted to elucidate the binding mechanism between tumor necrosis factor (TNF) and clinically relevant antagonists. None of these studies, however, have been conducted as close as possible to physiologic conditions, and so the relationship between the size distribution of TNF-antagonist complexes and the antagonists' biological activity or adverse effects remains elusive. Here, we characterized the binding stoichiometry and sizes of soluble TNF-antagonist complexes for adalimumab, infliximab, and etanercept that were formed in human serum and in phosphate-buffered saline (PBS). Fluorescence-detected sedimentation velocity analytical ultracentrifugation analyses revealed that adalimumab and infliximab formed a range of complexes with TNF, with the major complexes consisting of 3 molcules of the respective antagonist and one or 2 molcules of TNF. Considerably greater amounts of high-molecular-weight complexes were detected for infliximab in human serum. The emergence of peaks with higher sedimentation coefficients than the adalimumab monomer as a function of added human serum albumin (HSA) concentration in PBS suggested weak reversible interactions between HSA and immunoglobulins. Etanerept exclusively formed 1:1 complexes with TNF in PBS, and a small amount of complexes with higher stoichiometry was detected in human serum. Consistent with these biophysical characterizations, a reporter assay showed that adalimumab and infliximab, but not etanercept, exerted FcγRIIa- and FcγRIIIa-mediated cell signaling in the presence of TNF and that infliximab exhibited higher potency than adalimumab. This study shows that assessing distribution profiles in serum will contribute to a more comprehensive understanding of the in vivo behavior of therapeutic proteins.

Structural and binding properties of laminarin revealed by analytical ultracentrifugation and calorimetric analyses

One of the β-1,3-glucans, laminarin, has been widely used as a substrate for enzymes including endo-1,3-β-glucanase. To obtain quantitative information about the molecular interaction between laminarin and endo-1,3-β-glucanase, the structural properties of laminarin should be determined. The results from pioneering work using analytical ultracentrifugation for carbohydrate analysis showed that laminarin from Laminaria digitata predominantly exists as a single-chain species with approximately 5% of triple-helical species. Differential scanning calorimetry experiments did not show a peak assignable to the transition from triple-helix to single-chain, supporting the notion that a large proportion of laminarin is the single-chain species. The interaction of laminarin with an inactive variant of endo-1,3-β-glucanase from Cellulosimicrobium cellulans, E119A, was quantitatively analyzed using isothermal titration calorimetry. The binding was enthalpically driven and the binding affinity was approximately 10(6) M(-1). The results from binding stoichiometric analysis indicated that on average, E119A binds to laminarin in a 2:1 ratio. This seems to be reasonable, because laminarin mainly exists as a monomer, the apparent molecular mass of laminarin is 3.6 kDa, and E119A would have substrate-binding subsites corresponding to 6 glucose units. The analytical ultracentrifugation experiments could detect different complex species of laminarin and endo-1,3-β-glucanase.

Haem-dependent dimerization of PGRMC1/Sigma-2 receptor facilitates cancer proliferation and chemoresistance

Progesterone-receptor membrane component 1 (PGRMC1/Sigma-2 receptor) is a haem-containing protein that interacts with epidermal growth factor receptor (EGFR) and cytochromes P450 to regulate cancer proliferation and chemoresistance; its structural basis remains unknown. Here crystallographic analyses of the PGRMC1 cytosolic domain at 1.95 Å resolution reveal that it forms a stable dimer through stacking interactions of two protruding haem molecules. The haem iron is five-coordinated by Tyr113, and the open surface of the haem mediates dimerization. Carbon monoxide (CO) interferes with PGRMC1 dimerization by binding to the sixth coordination site of the haem. Haem-mediated PGRMC1 dimerization is required for interactions with EGFR and cytochromes P450, cancer proliferation and chemoresistance against anti-cancer drugs; these events are attenuated by either CO or haem deprivation in cancer cells. This study demonstrates protein dimerization via haem–haem stacking, which has not been seen in eukaryotes, and provides insights into its functional significance in cancer.

PGRMC1 binds to EGFR and cytochromes P450, and is known to be involved in cancer proliferation and in drug resistance. Here, the authors determine the structure of the cytosolic domain of PGRMC1, which forms a dimer via haem–haem stacking, and propose how this interaction could be involved in its function.

A multilaboratory comparison of calibration accuracy and the performance of external references in analytical ultracentrifugation

Analytical ultracentrifugation (AUC) is a first principles based method to determine absolute sedimentation coefficients and buoyant molar masses of macromolecules and their complexes, reporting on their size and shape in free solution. The purpose of this multi-laboratory study was to establish the precision and accuracy of basic data dimensions in AUC and validate previously proposed calibration techniques. Three kits of AUC cell assemblies containing radial and temperature calibration tools and a bovine serum albumin (BSA) reference sample were shared among 67 laboratories, generating 129 comprehensive data sets. These allowed for an assessment of many parameters of instrument performance, including accuracy of the reported scan time after the start of centrifugation, the accuracy of the temperature calibration, and the accuracy of the radial magnification. The range of sedimentation coefficients obtained for BSA monomer in different instruments and using different optical systems was from 3.655 S to 4.949 S, with a mean and standard deviation of (4.304 ± 0.188) S (4.4%). After the combined application of correction factors derived from the external calibration references for elapsed time, scan velocity, temperature, and radial magnification, the range of s-values was reduced 7-fold with a mean of 4.325 S and a 6-fold reduced standard deviation of ± 0.030 S (0.7%). In addition, the large data set provided an opportunity to determine the instrument-to-instrument variation of the absolute radial positions reported in the scan files, the precision of photometric or refractometric signal magnitudes, and the precision of the calculated apparent molar mass of BSA monomer and the fraction of BSA dimers. These results highlight the necessity and effectiveness of independent calibration of basic AUC data dimensions for reliable quantitative studies.

Effects of syringe material and silicone oil lubrication on the stability of pharmaceutical proteins

Currently, polymer-based prefillable syringes are being promoted to the pharmaceutical market because they provide an increased break resistance relative to traditionally used glass syringes. Despite this significant advantage, the possibility that barrel material can affect the oligomeric state of the protein drug exists. The present study was designed to compare the effect of different syringe materials and silicone oil lubrication on the protein aggregation. The stability of a recombinant fusion protein, abatacept (Orencia), and a fully human recombinant immunoglobulin G1, adalimumab (Humira), was assessed in silicone oil-free (SOF) and silicone oil-lubricated 1-mL glass syringes and polymer-based syringes in accelerated stress study. Samples were subjected to agitation stress, and soluble aggregate levels were evaluated by size-exclusion chromatography and verified with analytical ultracentrifugation. In accordance with current regulatory expectations, the amounts of subvisible particles resulting from agitation stress were estimated using resonant mass measurement and dynamic flow-imaging analyses. The amount of aggregated protein and particle counts were similar between unlubricated polymer-based and glass syringes. The most significant protein loss was observed for lubricated glass syringes. These results suggest that newly developed SOF polymer-based syringes are capable of providing biopharmaceuticals with enhanced physical stability upon shipping and handling. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 104:527–535, 2015

Structural studies of nucleic acid sensing Toll-like receptor

Toll-like receptors (TLRs) sense pathogen-associated molecular patterns originating from invading microorganism and evoke innate immune responses. Among TLRs, TLR3, TLR7, TLR8, and TLR9 are localized to endosomal membranes and are responsible for the recognition of nucleic acids. TLR7 and TLR8 recognize single stranded RNA. In addition, TLR7 and TLR8 are activated by small chemical compounds. TLR9 recognizes DNA containing Cytosine-phosphate-Guanine motif. Theses nucleic acid sensing TLRs are attractive therapeutic targets for the modulation of immune responses in the viral and bacterial infections and in the pathogenesis of autoimmune diseases. However, the structural basis for the nucleic acid recognition and signaling mechanisms remains to be elucidated. Therefore, we conducted crystallographic studies of these TLRs. Recently, we have determined the crystal structures of the extracellular domain of human TLR8 in the unliganded form and in the liganded forms with chemical ligands (Tanji et al., 2013). Both unliganded and liganded forms of TLR8 were dimer. Ligands were located at two equivalent positions in the dimerization interface. The ligand binding induced the reorganization of the preformed dimer to the activated dimer such that the C-terminal regions of the two protomers are in close proximity to enable the subsequent dimerization of the intracellular signaling domains and its interactions with adaptor proteins.

Effects of rotational speed on the hydrodynamic properties of pharmaceutical antibodies measured by analytical ultracentrifugation sedimentation velocity

Analytical ultracentrifugation sedimentation velocity (AUC-SV) has recently become one of the most important tools for the measurement of hydrodynamic properties of proteins. Although a number of studies using AUC-SV as applied to pharmaceutical antibodies have been conducted, the effect of rotational speed on molecular properties has not been systematically examined. The present study aimed to elucidate the influence of rotational speed on the hydrodynamic parameters of pharmaceutical antibodies. A monoclonal and a polyclonal antibody were studied by using AUC-SV at 5 different rotor speeds, and the acquired data were analyzed either by using the computer programs SEDFIT or UltraScan. The frictional ratio of the studied antibodies decreased at high rotor speeds, resulting in underestimation of molecular weight. The frictional ratio value of the monoclonal antibody measured at the low rotor speed was consistent with that of human immunoglobulin G1 computed from its three-dimensional structure. The best agreement between the measured molecular weight and the value calculated from the antibody sequence was achieved at the lower rotor speed. Similar to the results obtained using antibodies, AUC-SV analysis of human serum albumin revealed that the frictional ratio and apparent molecular weight behave in a speed-dependent manner. We deduced that the findings were mainly attributable to the hydrostatic pressure in the analytical ultracentrifuge. The current study implies that rotor speed should be carefully considered in antibody studies using AUC-SV.