Dynamic PRC1-CBX8 stabilizes a porous structure of chromatin condensates.

The compaction of chromatin is a prevalent paradigm in gene repression. Chromatin compaction is commonly thought to repress transcription by restricting chromatin accessibility. However, the spatial organisation and dynamics of chromatin compacted by gene-repressing factors are unknown. Using cryo-electron tomography, we solved the threedimensional structure of chromatin condensed by the Polycomb Repressive Complex 1 (PRC1) in a complex with CBX8. PRC1-condensed chromatin is porous and stabilised through multivalent dynamic interactions of PRC1 with chromatin. Mechanistically, positively charged residues on the internally disordered regions (IDRs) of CBX8 mask negative charges on the DNA to stabilize the condensed state of chromatin. Within condensates, PRC1 remains dynamic while maintaining a static chromatin structure. In differentiated mouse embryonic stem cells, CBX8-bound chromatin remains accessible. These findings challenge the idea of rigidly compacted polycomb domains and instead provides a mechanistic framework for dynamic and accessible PRC1-chromatin condensates.

Detection of gonadotropin-releasing hormone and its analogues in equine and canine urine by high-resolution data-independent acquisition.

Gonadotropin-releasing hormone (GnRH) and its synthetic analogues are considered banned substances by the racing industry. GnRH is used as a pharmaceutical to regulate the female oestrous cycle, but the hormone is also thought to increase the production of testosterone in male animals. Using liquid chromatography in conjunction with high-resolution mass spectrometry (LC-HRMS) and data-independent acquisition (DIA), a method is presented for the detection of intact and truncated peptides of GnRH and its analogues down to the low picogram level in equine urine. The study of the catabolism of GnRH and analogues in plasma, combined with the analysis of urine from administration studies, reveals a common pattern of peptide catabolites that can be used to guide the design of MS-based screens for this class of drugs. This culminated in the successful detection of the peptide in two out-of-competition canine urine samples.

The detection of a synthetic Interleukin-1 receptor antagonist peptide in a seized product from a racing stable.

A synthetic Interleukin-1 receptor antagonist peptide with the sequence Acetyl-Phe-Glu-Trp-Thr-Pro-Gly-Tyr-Trp-Gln-Pro-Tyr-Ala-Leu-Pro-Leu-OH has been identified in a vial seized during a stable inspection. The use of peptide-based Interleukin-1 receptor antagonists as anti-inflammatory agents has not been previously reported, making this peptide the first in a new class of sports doping peptides. The peptide has been characterized by high-resolution mass spectrometry and a detection method developed based on solid-phase extraction and liquid chromatography - triple quadrupole mass spectrometry. Using in vitro and in vivo models to study the properties of the peptide after administration, the peptide was shown to be highly unstable in plasma and was not detected in urine after administration in a rat. The poor stability of the peptide makes detection challenging but also suggests that it has limited effectiveness as an anti-inflammatory drug. Copyright © 2015 John Wiley & Sons, Ltd.

Targeting of Fn14 Prevents Cancer-Induced Cachexia and Prolongs Survival.

The cytokine TWEAK and its cognate receptor Fn14 are members of the TNF/TNFR superfamily and are upregulated in tumors. We found that Fn14, when expressed in tumors, causes cachexia and that antibodies against Fn14 dramatically extended lifespan by inhibiting tumor-induced weight loss although having only moderate inhibitory effects on tumor growth. Anti-Fn14 antibodies prevented tumor-induced inflammation and loss of fat and muscle mass. Fn14 signaling in the tumor, rather than host, is responsible for inducing this cachexia because tumors in Fn14- and TWEAK-deficient hosts developed cachexia that was comparable to that of wild-type mice. These results extend the role of Fn14 in wound repair and muscle development to involvement in the etiology of cachexia and indicate that Fn14 antibodies may be a promising approach to treat cachexia, thereby extending lifespan and improving quality of life for cancer patients.

C9ORF72, implicated in amytrophic lateral sclerosis and frontotemporal dementia, regulates endosomal trafficking.

Intronic expansion of a hexanucleotide GGGGCC repeat in the chromosome 9 open reading frame 72 (C9ORF72) gene is the major cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. However, the cellular function of the C9ORF72 protein remains unknown. Here, we demonstrate that C9ORF72 regulates endosomal trafficking. C9ORF72 colocalized with Rab proteins implicated in autophagy and endocytic transport: Rab1, Rab5, Rab7 and Rab11 in neuronal cell lines, primary cortical neurons and human spinal cord motor neurons, consistent with previous predictions that C9ORF72 bears Rab guanine exchange factor activity. Consistent with this notion, C9ORF72 was present in the extracellular space and as cytoplasmic vesicles. Depletion of C9ORF72 using siRNA inhibited transport of Shiga toxin from the plasma membrane to Golgi apparatus, internalization of TrkB receptor and altered the ratio of autophagosome marker light chain 3 (LC3) II:LC3I, indicating that C9ORF72 regulates endocytosis and autophagy. C9ORF72 also colocalized with ubiquilin-2 and LC3-positive vesicles, and co-migrated with lysosome-stained vesicles in neuronal cell lines, providing further evidence that C9ORF72 regulates autophagy. Investigation of proteins interacting with C9ORF72 using mass spectrometry identified other proteins implicated in ALS; ubiquilin-2 and heterogeneous nuclear ribonucleoproteins, hnRNPA2/B1 and hnRNPA1, and actin. Treatment of cells overexpressing C9ORF72 with proteasome inhibitors induced the formation of stress granules positive for hnRNPA1 and hnRNPA2/B1. Immunohistochemistry of C9ORF72 ALS patient motor neurons revealed increased colocalization between C9ORF72 and Rab7 and Rab11 compared with controls, suggesting possible dysregulation of trafficking in patients bearing the C9ORF72 repeat expansion. Hence, this study identifies a role for C9ORF72 in Rab-mediated cellular trafficking.

A high-throughput LC-MS/MS screen for GHRP in equine and human urine, featuring peptide derivatization for improved chromatography.

The growth hormone releasing peptides (GHRPs) hexarelin, ipamorelin, alexamorelin, GHRP-1, GHRP-2, GHRP-4, GHRP-5, and GHRP-6 are all synthetic met-enkephalin analogues that include unnatural D-amino acids. They were designed specifically for their ability to stimulate growth hormone release and may serve as performance enhancing drugs. To regulate the use of these peptides within the horse racing industry and by human athletes, a method is presented for the extraction, derivatization, and detection of GHRPs from equine and human urine. This method takes advantage of a highly specific solid-phase extraction combined with a novel derivatization method to improve the chromatography of basic peptides. The method was validated with respect to linearity, repeatability, intermediate precision, specificity, limits of detection, limits of confirmation, ion suppression, and stability. As proof of principle, all eight GHRPs or their metabolites could be detected in urine collected from rats after intravenous administration.

A high throughput screen for 17 Dermorphin peptides in equine and human urine and equine plasma.

The Dermorphins are a family of peptides that act as potent agonists of the opioid µ receptor. Originally identified as a seven amino acid peptide on the skin of the South American Phyllomedusa frog, peptide chemists have since developed a large number of Dermorphin variants, many with superior opioid activity to the original peptide. Dermorphins are unique among the peptide opioid agonists as they appear to have a limited ability to cross the blood brain barrier, producing effects on both the central and peripheral nervous systems. It is this ability of Dermorphins to provide central anaesthesia after intravenous or subcutaneous administration that allows their use as analogues of the opioid class of drugs. Recently, illicit use of the Dermorphin peptide in the racing industry has shown the need for an analytical method to control the use of these peptides. We present a high-throughput liquid chromatography-tandem mass spectrometry screen for 17 Dermorphin peptides in equine urine and plasma with limits of detection down to 5 pg/mL. The peptide extraction technique is also suitable for use in human urine.

N-linked glycosylation modulates dimerization of protein disulfide isomerase family A member 2 (PDIA2).

Protein disulfide isomerase (PDI) family members are important enzymes for the correct folding and maturation of proteins that transit or reside in the endoplasmic reticulum (ER). The human PDI family comprises at least 19 members that differ in cell type expression, substrate specificity and post-translational modifications. PDI family A member 2 (PDIA2, previously known as PDIp) has a similar domain structure to prototypical PDI (also known as PDIA1), but the function and post-translational modifications of PDIA2 remain poorly understood. Unlike most PDI family members, PDIA2 contains three predicted N-linked glycosylation sites. By site-directed mutagenesis and enzymatic deglycosylation, we show here that all three Asn residues within the potential N-linked glycosylation sites of human PDIA2 (N127, N284 and N516) are glycosylated in human cells. Furthermore, mutation of N284 to glycosylation-null Gln increases formation of a highly stable disulfide-bonded PDIA2 dimer. Nevertheless, in HeLa cells, both wild-type and N127/284/516Q mutant PDIA2 proteins localize to the ER, but not the ER-Golgi intermediate compartment, suggesting that glycosylation is important for PDIA2 protein-protein interactions but not subcellular localization. Finally, we identified human major histocompatibility complex class 1 antigens (HLA-A,B,C) as potential binding partners of PDIA2, suggesting an involvement for PDIA2 in antigen presentation in addition to its previously described roles in autoimmunity and Parkinson's disease. These results further characterize this poorly defined member of the PDI family.

Caspase inhibitors of the P35 family are more active when purified from yeast than bacteria.

Many insect viruses express caspase inhibitors of the P35 superfamily, which prevent defensive host apoptosis to enable viral propagation. The prototypical P35 family member, AcP35 from Autographa californica M nucleopolyhedrovirus, has been extensively studied. Bacterially purified AcP35 has been previously shown to inhibit caspases from insect, mammalian and nematode species. This inhibition occurs via a pseudosubstrate mechanism involving caspase-mediated cleavage of a "reactive site loop" within the P35 protein, which ultimately leaves cleaved P35 covalently bound to the caspase's active site. We observed that AcP35 purifed from Saccharomyces cerevisae inhibited caspase activity more efficiently than AcP35 purified from Escherichia coli. This differential potency was more dramatic for another P35 family member, MaviP35, which inhibited human caspase 3 almost 300-fold more potently when purified from yeast than bacteria. Biophysical assays revealed that MaviP35 proteins produced in bacteria and yeast had similar primary and secondary structures. However, bacterially produced MaviP35 possessed greater thermal stability and propensity to form higher order oligomers than its counterpart purified from yeast. Caspase 3 could process yeast-purified MaviP35, but failed to detectably cleave bacterially purified MaviP35. These data suggest that bacterially produced P35 proteins adopt subtly different conformations from their yeast-expressed counterparts, which hinder caspase access to the reactive site loop to reduce the potency of caspase inhibition, and promote aggregation. These data highlight the differential caspase inhibition by recombinant P35 proteins purified from different sources, and caution that analyses of bacterially produced P35 family members (and perhaps other types of proteins) may underestimate their activity.

Intracellular production of recombinant serpins in yeast.

Yeast are a valuable system for recombinant serpin production due to their ability to synthesize large amounts of heterologous gene products as well as their expression of folding chaperones and lack of endogenous serpin genes. In this chapter, we describe a method for intracellular expression of cytoplasmic serpins in the yeast Pichia pastoris. We also give details on how this system can be exploited to produce polymer-forming mutants of secretory serpins.

The subtilisin-like protease AprV2 is required for virulence and uses a novel disulphide-tethered exosite to bind substrates.

Many bacterial pathogens produce extracellular proteases that degrade the extracellular matrix of the host and therefore are involved in disease pathogenesis. Dichelobacter nodosus is the causative agent of ovine footrot, a highly contagious disease that is characterized by the separation of the hoof from the underlying tissue. D. nodosus secretes three subtilisin-like proteases whose analysis forms the basis of diagnostic tests that differentiate between virulent and benign strains and have been postulated to play a role in virulence. We have constructed protease mutants of D. nodosus; their analysis in a sheep virulence model revealed that one of these enzymes, AprV2, was required for virulence. These studies challenge the previous hypothesis that the elastase activity of AprV2 is important for disease progression, since aprV2 mutants were virulent when complemented with aprB2, which encodes a variant that has impaired elastase activity. We have determined the crystal structures of both AprV2 and AprB2 and characterized the biological activity of these enzymes. These data reveal that an unusual extended disulphide-tethered loop functions as an exosite, mediating effective enzyme-substrate interactions. The disulphide bond and Tyr92, which was located at the exposed end of the loop, were functionally important. Bioinformatic analyses suggested that other pathogenic bacteria may have proteases that utilize a similar mechanism. In conclusion, we have used an integrated multidisciplinary combination of bacterial genetics, whole animal virulence trials in the original host, biochemical studies, and comprehensive analysis of crystal structures to provide the first definitive evidence that the extracellular secreted proteases produced by D. nodosus are required for virulence and to elucidate the molecular mechanism by which these proteases bind to their natural substrates. We postulate that this exosite mechanism may be used by proteases produced by other bacterial pathogens of both humans and animals.

Kinetic instability of the serpin Z alpha1-antitrypsin promotes aggregation.

The serpinopathies encompass a large number of diseases caused by inappropriate conformational change and self-association (polymerization) of a serpin (serine proteinase inhibitor) molecule. The most common serpinopathy is alpha(1)-antitrypsin (alpha(1)AT) deficiency, which is associated with an increased risk for liver cirrhosis, hepatocellular carcinoma and early-onset emphysema. The Z variant of alpha(1)AT, which accounts for 95% of all cases of alpha(1)AT deficiency, polymerizes during synthesis and after secretion. Here, we show using intrinsic and extrinsic fluorescence probes that Z alpha(1)AT exists in a non-native conformation. We examined the thermodynamic stability by transverse urea gradient gel electrophoresis, thermal denaturation and equilibrium guanidine hydrochloride unfolding and found that, despite structural differences between the two proteins, wild-type alpha(1)AT and Z alpha(1)AT display similar unfolding pathways and thermodynamic stabilities. Far-UV circular dichroism and bis-ANS (4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid, dipotassium salt) fluorescence suggest that the intermediate ensembles formed during unfolding of wild-type alpha(1)AT and Z alpha(1)AT are characterized by similar structural features. Kinetic analysis of the unfolding transition showed that Z alpha(1)AT unfolds at least 1.5-fold faster than the wild type. The biological implications of these data are discussed.

Expression, purification and characterization of recombinant Z alpha(1)-antitrypsin--the most common cause of alpha(1)-antitrypsin deficiency.

Alpha(1)-antitrypsin (alpha(1)AT), the most abundant proteinase inhibitor circulating in the blood, protects extracellular matrix proteins of the lung against proteolytic destruction by neutrophil elastase. alpha(1)AT deficiency predisposes patients to emphysema, juvenile cirrhosis and hepatocellular carcinoma. Over 90% of clinical cases of severe alpha(1)AT deficiency are caused by the Z variant (E342K) of alpha(1)AT. The presence of the Z mutation results in misfolding and polymerization of alpha(1)AT. Due to its inherent propensity to polymerize there are no reported cases of recombinant Z alpha(1)AT production. This has created a major impediment to studying the effect of the Z mutation on alpha(1)AT. Here we report our attempts to produce recombinant Z alpha(1)AT using both Escherichia coli and Pichia pastoris as host systems. Using a range of expression vectors in E. coli we were unable to produce soluble active Z alpha(1)AT. Cytosolic expression of the Z alpha(1)AT gene in P. pastoris was successful. Monomeric and active recombinant Z alpha(1)AT was purified from the yeast cytosol using affinity chromatography and anion exchange chromatography. Biochemical analyses demonstrated that the recombinant Z alpha(1)AT has identical properties to its native counterpart purified from plasma of patients homozygous for the Z allele. A recombinant source of pathological Z alpha(1)AT will increase the chances of elucidating the mechanism of its polymerization and thus the development of therapeutic strategies.