Enterokinase, the initiator of intestinal digestion, is a mosaic protease composed of a distinctive assortment of domains

Functional maturation of preterm intestinal epithelium through CFTR activation

Preterm birth disrupts intestinal epithelial maturation, impairing digestive and absorptive functions. This study integrates analysis of single-cell RNA sequencing datasets, spanning fetal to adult stages, with human preterm intestinal models derived from the ileal tissue of preterm infants. We investigate the potential of extracellular vesicles (EVs) derived from human Wharton's jelly mesenchymal stem cells to promote intestinal maturation. Distinct enterocyte differentiation trajectories are identified during the transition from immature to mature stages of human intestinal development. EV treatment, particularly with the EV39 line, significantly upregulates maturation-specific gene expression related to enterocyte function. Gene set enrichment analysis reveals an enrichment of TGFβ1 signaling pathways, and proteomic analysis identifies TGFβ1 and FGF2 as key mediators of EV39's effects. These treatments enhance cell proliferation, epithelial barrier integrity, and fatty acid uptake, primarily through CFTR-dependent mechanisms-unique to human preterm models, not observed in mouse intestinal organoids. This highlights the translational potential of EV39 and CFTR activation in promoting the functional maturation of the premature human intestine.

Inducible, but not constitutive, pancreatic REG/Reg isoforms are regulated by intestinal microbiota and pancreatic diseases

The REG / Reg gene locus encodes for a conserved family of potent antimicrobial but also pancreatitis-associated proteins. Here we investigated whether REG/Reg family members differ in their baseline expression levels and abilities to be regulated in the pancreas and gut upon perturbations. We found, in human and mouse, pancreas and gut differed in REG / Reg isoform levels and preferences, with duodenum most resembling the pancreas. Pancreatic acinar cells and intestinal enterocytes were the dominant REG producers. Intestinal symbiotic microbes regulated the expression of the same, select Reg members in gut and pancreas. These Reg members had the most STAT3-binding sites close to the transcription start sites and were partially IL-22 dependent. We thus categorized them as "inducible" and others as "constitutive". Indeed, also in models of pancreatic-ductal adenocarcinoma and pancreatitis, only inducible Reg members were upregulated in pancreas. While intestinal Reg expression remained unchanged upon pancreatic perturbation, pancreatitis altered the microbial composition of the duodenum and feces shortly after disease onset. Our study reveals differential usage and regulation of REG / Reg isoforms as a mechanism for tissue-specific innate immunity, highlights the intimate connection of pancreas and duodenum, and implies a gut-to-pancreas communication axis resulting in a coordinated Reg response.

Production of a Bacteriocin Like Protein PEG 446 from Clostridium tyrobutyricum NRRL B-67062

Clostridium tyrobutyricum strain NRRL B-67062 was previously isolated from an ethanol production facility and shown to produce high yields of butyric acid. In addition, the cell-free supernatant of the fermentation broth from NRRL B-67062 contained antibacterial activity against certain Gram-positive bacteria. To determine the source of this antibacterial activity, we report the genome and genome mining of this strain. The complete genome of NRRL B-67062 showed one circular chromosome of 3,242,608 nucleotides, 3114 predicted coding sequences, 79 RNA genes, and a G+C content of 31.0%. Analyses of the genome data for genes potentially associated with antimicrobial features were sought after by using BAGEL-4 and anti-SMASH databases. Among the leads, a polypeptide of 66 amino acids (PEG 446) contains the DUF4177 domain, which is an uncharacterized highly conserved domain (pfam13783). The cloning and expression of the peg446 gene in Escherichia coli and Bacillus subtilis confirmed the antibacterial property against Lactococcus lactis LM 0230, Limosilactobacillus fermentum 0315-25, and Listeria innocua NRRL B-33088 by gel overlay and well diffusion assays. Molecular modeling suggested that PEG 446 contains one alpha-helix and three anti-parallel short beta-sheets. These results will aid further functional studies and facilitate simultaneously fermentative production of both butyric acid and a putative bacteriocin from agricultural waste and lignocellulosic biomass materials.

Electrochemical Impedance Spectroscopy for the Sensing of the Kinetic Parameters of Engineered Enzymes

The study presents a promising approach to enzymatic kinetics using Electrochemical Impedance Spectroscopy (EIS) to assess fundamental parameters of modified enteropeptidases. Traditional methods for determining these parameters, while effective, often lack versatility and convenience, especially under varying environmental conditions. The use of EIS provides a novel approach that overcomes these limitations. The enteropeptidase underwent genetic modification through the introduction of single amino acid modifications to assess their effect on enzyme kinetics. However, according to the one-sample t-test results, the difference between the engineered enzymes and hEKL was not statistically significant by conventional criteria. The kinetic parameters were analyzed using fluorescence spectroscopy and EIS, which was found to be an effective tool for the real-time measurement of enzyme kinetics. The results obtained through EIS were not significantly different from those obtained through traditional fluorescence spectroscopy methods (p value >> 0.05). The study validates the use of EIS for measuring enzyme kinetics and provides insight into the effects of specific amino acid changes on enteropeptidase function. These findings have potential applications in biotechnology and biochemical research, suggesting a new method for rapidly assessing enzymatic activity.

Spatial position is a key determinant of N-glycan functionality of the scavenger receptor cysteine-rich domain of human hepsin

The scavenger receptor cysteine-rich (SRCR) domain is a key constituent in diverse proteins. N-glycosylation is important in protein expression and function. In the SRCR domain of different proteins, N-glycosylation sites and functionality vary substantially. In this study, we examined the importance of N-glycosylation site positions in the SRCR domain of hepsin, a type II transmembrane serine protease involved in many pathophysiological processes. We analysed hepsin mutants with alternative N-glycosylation sites in the SRCR and protease domains using three-dimensional modelling, site-directed mutagenesis, HepG2 cell expression, immunostaining, and western blotting. We found that the N-glycan function in the SRCR domain in promoting hepsin expression and activation on the cell surface cannot be replaced by alternatively created N-glycans in the protease domain. Within the SRCR domain, the presence of an N-glycan in a confined surface area was essential for calnexin-assisted protein folding, endoplasmic reticulum (ER) exiting, and zymogen activation of hepsin on the cell surface. Hepsin mutants with alternative N-glycosylation sites on the opposite side of the SRCR domain were trapped by ER chaperones, resulting in the activation of the unfolded protein response in HepG2 cells. These results indicate that the spatial N-glycan positioning in the SRCR domain is a key determinant in the interaction with calnexin and subsequent cell surface expression of hepsin. These findings may help to understand the conservation and functionality of N-glycosylation sites in the SRCR domains of different proteins.

Characterization of digestive proteases in the gut of a basal deuterostome

Digestive systems are complex organs that allow organisms to absorb energy from their environment to fuel vital processes such as growth, development and the maintenance of homeostasis. A comprehensive understanding of digestive physiology is therefore essential to fully understand the energetics of an organism. The digestion of proteins is of particular importance because most heterotrophic organisms are not able to synthesize all essential amino acids. While Echinoderms are basal deuterostomes that share a large genetic similarity with vertebrates, their digestion physiology remains largely unexplored. Using a genetic approach, this work demonstrated that several protease genes including an enteropeptidase, aminopeptidase, carboxypeptidase and trypsin involved in mammalian digestive networks are also found in sea urchin larvae. Through characterization including perturbation experiments with different food treatments and pharmacological inhibition of proteases using specific inhibitors, as well as transcriptomic analysis, we conclude that the trypsin-2 gene codes for a crucial enzyme for protein digestion in Strongylocentrotus purpuratus. Measurements of in vivo digestion rates in the transparent sea urchin larva were not altered by pharmacological inhibition of trypsin (using soybean trypsin inhibitor) or serine proteases (aprotinin), suggesting that proteases are not critically involved in the initial step of microalgal breakdown. This work provides new insights into the digestive physiology of a basal deuterostome and allows comparisons from the molecular to the functional level in the digestive systems of vertebrates and mammals. This knowledge will contribute to a better understanding for conserved digestive mechanisms that evolved in close interaction with their biotic and abiotic environment.

Novel Non-duct-to-Mucosa Pancreaticojejunostomy Reconstruction After Pancreaticoduodenectomy: Focus on the Occurrence of Post-pancreatectomy Hemorrhage and Intra-abdominal Abscess

BACKGROUND

Postoperative pancreatic fistulas (POPFs) are considered inevitable in some patients after pancreaticoduodenectomy (PD), and measures to minimize their clinical impact are needed. Postpancreatectomy hemorrhage (PPH) and intra-abdominal abscess (IAA) are the most severe POPF-related complications, and concomitant leakage of contaminated intestinal content is considered the main cause. An innovative method, modified non-duct-to-mucosa pancreaticojejunostomy (TPJ), was created to prevent concomitant leakage of intestinal content, and its effectiveness was compared between two periods.

METHODS

All PD patients undergoing pancreaticojejunostomy from 2012 to 2021 were included. The TPJ group consisted of 529 patients recruited from January 2018 to December 2021. A total of 535 patients receiving the conventional method (CPJ) from January 2012 to June 2017 were used as a control group. PPH and POPF were defined according to the International Study Group of Pancreatic Surgery definition, but only PPH grade C was included for analysis. An IAA was defined as a collection of postoperative fluid managed by CT-guided drainage with documental culture.

RESULTS

There were no significant differences in the rate of POPF between the two groups (46.0% vs. 44.8%; p = 0.700). Furthermore, the percentages of bile in the drainage fluid in the TPJ and CPJ groups were 2.3% and 9.2%, respectively (p < 0.001). Lower proportions of PPH (0.9% vs. 6.5%; p < 0.001) and IAA (5.7% vs. 10.8%; p < 0.001) were observed for TPJ than for CPJ. On adjusted models, TPJ was significantly associated with a lower rate of PPH (odds ratio [OR] 0.132, 95% confidence interval [CI] 0.051-0.343; p < 0.001) and IAA (OR 0.514, 95% CI 0.349-0.758; p = 0.001) than CPJ.

CONCLUSIONS

TPJ is feasible to be performed and is associated with a similar rate of POPF but a lower percentage of concomitant bile in the drainage fluid and subsequent rates of PPH and IAA than CPJ.

Cryo-EM structures reveal the activation and substrate recognition mechanism of human enteropeptidase

Enteropeptidase (EP) initiates intestinal digestion by proteolytically processing trypsinogen, generating catalytically active trypsin. EP dysfunction causes a series of pancreatic diseases including acute necrotizing pancreatitis. However, the molecular mechanisms of EP activation and substrate recognition remain elusive, due to the lack of structural information on the EP heavy chain. Here, we report cryo-EM structures of human EP in inactive, active, and substrate-bound states at resolutions from 2.7 to 4.9 Å. The EP heavy chain was observed to clamp the light chain with CUB2 domain for substrate recognition. The EP light chain N-terminus induced a rearrangement of surface-loops from inactive to active conformations, resulting in activated EP. The heavy chain then served as a hinge for light-chain conformational changes to recruit and subsequently cleave substrate. Our study provides structural insights into rearrangements of EP surface-loops and heavy chain dynamics in the EP catalytic cycle, advancing our understanding of EP-associated pancreatitis.

Enzyme-mediated intratumoral self-assembly of nanotheranostics for enhanced imaging and tumor therapy

Enzyme-mediated intratumoral self-assembled (EMISA) nanotheranostics represent a new class of smart agents for combined imaging and therapy of cancer. Cancer cells overexpress various enzymes that are essential for high metabolism, fast proliferation, and tissue invasion and metastasis. By conjugating small molecules that contain an enzyme-specific cleavage site to appropriate chemical linkers, it is possible to induce self-assembly of nanostructures in tumor cells having the target enzyme. This approach of injecting small theranostic molecules that eventually become larger nanotheranostics in situ avoids some of the major limitations that are encountered when injecting larger, pre-assembled nanotheranostics. The advantage of EMISA nanotheranostics include the avoidance of nonspecific uptake and rapid clearance by phagocytic cells, increased cellular accumulation, reduced drug efflux and prolonged cellular exposure time, all of which lead to an amplified imaging signal and therapeutic efficacy. We review here the different approaches that can be used for preparing EMISA-based organic, inorganic, or organic/inorganic hybrid nanotheranostics based on noncovalent interactions and/or covalent bonding. Imaging examples are shown for fluorescence imaging, nuclear imaging, photoacoustic imaging, Raman imaging, computed tomography imaging, bioluminescent imaging, and magnetic resonance imaging. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Biology-Inspired Nanomaterials > Peptide-Based Structures.

Design, Synthesis, and Biological Evaluation of a Novel Series of 4-Guanidinobenzoate Derivatives as Enteropeptidase Inhibitors with Low Systemic Exposure for the Treatment of Obesity

To discover a novel series of potent inhibitors of enteropeptidase, a membrane-bound serine protease localized to the duodenal brush border, 4-guanidinobenzoate derivatives were evaluated with minimal systemic exposure. The 1c docking model enabled the installation of an additional carboxylic acid moiety to obtain an extra interaction with enteropeptidase, yielding 2a. The oral administration of 2a significantly elevated the fecal protein output, a pharmacodynamic marker, in diet-induced obese (DIO) mice, whereas subcutaneous administration did not change this parameter. Thus, systemic exposure of 2a was not required for its pharmacological effects. Further optimization focusing on the in vitro IC₅₀ value and T_1/2, an indicator of dissociation time, followed by enhanced in vivo pharmacological activity based on the ester stability of the compounds, revealed two series of potent enteropeptidase inhibitors, a dihydrobenzofuran analogue ((S)-5b, SCO-792) and phenylisoxazoline (6b), which exhibited potent anti-obesity effects despite their low systemic exposure following their oral administration to DIO rats.

Deep whole-genome resequencing sheds light on the distribution and effect of amphioxus SNPs

BACKGROUND

Amphioxus is a model organism for vertebrate evolutionary research. The significant contrast between morphological phenotypic similarity and high-level genetic polymorphism among amphioxus populations has aroused scientists' attention. Here we resequenced 21 amphioxus genomes to over 100X depth and mapped them to a haploid reference.

RESULTS

More than 11.5 million common SNPs were detected in the amphioxus population, which mainly affect genes enriched in ion transport, signal transduction and cell adhesion, while protein structure analysis via AlphaFold2 revealed that these SNPs fail to bring effective structural variants.

CONCLUSIONS

Our work provides explanation for "amphioxus polymorphism paradox" in a micro view, and generates an enhanced genomic dataset for amphioxus research.

Designing bioresponsive nanomaterials for intracellular self-assembly

Supramolecular assemblies are essential components of living organisms. Cellular scaffolds, such as the cytoskeleton or the cell membrane, are formed via secondary interactions between proteins or lipids and direct biological processes such as metabolism, proliferation and transport. Inspired by nature’s evolution of function through structure formation, a range of synthetic nanomaterials has been developed in the past decade, with the goal of creating non-natural supramolecular assemblies inside living mammalian cells. Given the intricacy of biological pathways and the compartmentalization of the cell, different strategies can be employed to control the assembly formation within the highly crowded, dynamic cellular environment. In this Review, we highlight emerging molecular design concepts aimed at creating precursors that respond to endogenous stimuli to build nanostructures within the cell. We describe the underlying reaction mechanisms that can provide spatial and temporal control over the subcellular formation of synthetic nanostructures. Showcasing recent advances in the development of bioresponsive nanomaterials for intracellular self-assembly, we also discuss their impact on cellular function and the challenges associated with establishing structure–bioactivity relationships, as well as their relevance for the discovery of novel drugs and imaging agents, to address the shortfall of current solutions to pressing health issues.

Creating artificial nanostructures inside living cells requires the careful design of molecules that can transform into active monomers within a complex cellular environment. This Review explores the recent development of bioresponsive precursors for the controlled formation of intracellular supramolecular assemblies.

The discovery and development of transmembrane serine protease 2 (TMPRSS2) inhibitors as candidate drugs for the treatment of COVID-19

INTRODUCTION

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has caused the devastating pandemic named coronavirus disease 2019 (COVID-19). Unfortunately, the discovery of antiviral agents to combat COVID-19 is still an unmet need. Transmembrane serine protease 2 (TMPRSS2) is an important mediator in viral infection and thus, TMPRRS2 inhibitors may be attractive agents for COVID-19 treatment.

AREAS COVERED

This review article discusses the role of TMPRSS2 in SARS-CoV-2 cell entry and summarizes the inhibitors of TMPRSS2 and their potential anti-SARS activity. Two known TMPRSS2 inhibitors, namely camostat and nafamostat, approved drugs for the treatment of pancreatitis, are under clinical trials as potential drugs against COVID-19.

EXPERT OPINION

Due to the lack of the crystal structure of TMPRSS2, homology models have been developed to study the interactions of known inhibitors, including repurposed drugs, with the enzyme. However, novel TMPRSS2 inhibitors have been identified through high-throughput screening, and appropriate assays studying their in vitro activity have been set up. The discovery of TMPRSS2's crystal structure will facilitate the rational design of novel inhibitors and in vivo studies and clinical trials will give a clear answer if TMPRSS2 inhibitors could be a new weapon against COVID-19.

The Global Status and Trends of Enteropeptidase: A Bibliometric Study

Background

Enteropeptidase (EP) is a type II transmembrane serine protease and a physiological activator of trypsinogen. Extensive studies related to EP have been conducted to date. However, no bibliometric analysis has systematically investigated this theme. Our study aimed to visualize the current landscape and frontier trends of scientific achievements on EP, provide an overview of the past 120 years and insights for researchers and clinicians to facilitate future collaborative research and clinical intervention.

Methods

Quantitative analysis of publications relating to EP from 1900 to 2020 was interpreted and graphed through the Science Citation Index Expanded of Web of Science Core Collection (limited to SCIE). Microsoft office 2019, GraphPad Prism 8, VOSviewer, and R-bibliometrix were used to conduct the bibliometric analysis.

Results

From 1900 to 2020, a total of 1,034 publications were retrieved. The USA had the largest number of publications, making the greatest contribution to the topic (n = 260, 25.15%). Active collaborations between countries/regions were also enrolled. Grant and Hermontaylor were perhaps the most impactful researchers in the landscape of EP. Protein Expression and Purification and the Journal of Biological Chemistry were the most prevalent (79/1,034, 7.64%) and cited journals (n = 2,626), respectively. Using the top 15 citations and co-citations achievements clarified the theoretical basis of the EP research field. Important topics mainly include the structure of EP, the affective factors for activating substrates by EP, EP-related disorders, and inhibitors of EP.

Conclusion

Based on the bibliometric analysis, we have gained a comprehensive analysis of the global status and research frontiers of studies investigating EP, which provides some guidance and reference for researchers and clinicians engaged in EP research.

A combination strategy of solubility enhancers for effective production of soluble and bioactive human enterokinase

Enterokinase is one of the hydrolases that catalyze hydrolysis to regulate biological processes in intestinal visceral mucosa. Enterokinase plays an essential role in accelerating the process of protein digestion as it converts trypsinogen into active trypsin by accurately recognizing and cleaving a specific peptide sequence, (Asp)4-Lys. Due to its exceptional substrate specificity, enterokinase is widely used as a versatile molecular tool in various bioprocessing, especially in removing fusion tags from recombinant proteins. Despite its biotechnological importance, mass production of soluble enterokinase in bacteria still remains an unsolved challenge. Here, we present an effective production strategy of human enterokinase using tandemly linked solubility enhancers consisting of thioredoxin, phosphoglycerate kinase or maltose-binding protein. The resulting enterokinases exhibited significantly enhanced solubility and bacterial expression level while retaining enzymatic activity, which demonstrates that combinatorial design of fusion proteins has the potential to provide an efficient way to produce recombinant proteins in bacteria.

Activation of Human Pancreatic Proteolytic Enzymes: The Role of Enteropeptidase and Trypsin

The role of enteropeptidase and trypsin in the process by which pancreatic proteolytic zymogens are converted into active enzymes has been investigated in the past, using purified enzymes and proenzymes of animal origin. In the present study, we wanted to study this process under conditions which come near to the physiological situation, which prevails in the human duodenum and upper small intestine.

Patients and Methods

Duodenal contents were collected from 2 patients with intestinal enteropeptidase deficiency. The samples expressed no tryptic activity and were used as the source of zymogens. Enteropeptidase or trypsin was added to these samples and the process of zymogen activation was followed by measuring trypsin and chymotrypsin activities.

Results

When exogenous trypsin was added to the duodenal contents of patients with enteropeptidase deficiency, having no tryptic activity, activation of intrinsic trypsinogen was not observed. When purified porcine or human enteropeptidase was added to the same samples of duodenal contents, this resulted in a rapid, dose-dependent activation of trypsinogen followed by the activation of chymotrypsinogen.

Conclusion

The study underlines the key role of enteropeptidase in the cascade process, which leads to the presence of active proteolytic enzymes in the human small intestine. The results also explain why patients with congenital deficiency of enteropeptidase are unable to activate trypsinogen by alternative pathways and therefore suffer from a severe disturbance of protein digestion with failure to thrive at young age, hypoproteinemia, and anemia.

Repaglinide-Induced Acute Pancreatitis

Acute pancreatitis is a common reason for hospitalization in the United States and can have a high degree of morbidity and mortality if not treated appropriately. Establishing the diagnosis and following guideline-directed medical therapy are both important. In the Western world, the most common causes include acute alcohol overuse, hypertriglyceridemia, gallstone pancreatitis, post-instrumentation including endoscopic cholangiopancreatography, and medication side effects. Our team describes the case of an 84-year-old male that was found to have acute pancreatitis secondary to repaglinide, a commonly used medication for the management of diabetes mellitus. The diagnosis was made based on the imaging findings, physical examination, and the corresponding laboratory markers. The patient was also found to have a blood-alcohol level at baseline and triglyceride levels within normal range. The patient’s symptoms resolved with the cessation of repaglinide administration. Our team hopes to make the medical community more aware of the potential association between repaglinide and the potentially rapidly debilitating disease. 

Discovery of a novel series of guanidinebenzoates as gut-restricted enteropeptidase and trypsin dual inhibitors for the treatment of metabolic syndrome

A novel series of guanidinebenzoate enteropeptidase and trypsin dual inhibitors has been discovered and SAR studies were conducted. Optimization was focused on improving properties for gut restriction, including increased aqueous solubility, lower cellular permeability, and reduced oral bioavailability. Lead compounds were identified with efficacy in a mouse fecal protein excretion study.

Crystal structure of inhibitor-bound human MSPL that can activate high pathogenic avian influenza

The structure of extracellular domain of MSPL and inhibitor complex helps to understand the TTSP functions, including TMPRSS2, and provides the insights of the infection of influenza and SARS-CoV.

Infection of certain influenza viruses is triggered when its HA is cleaved by host cell proteases such as proprotein convertases and type II transmembrane serine proteases (TTSP). HA with a monobasic motif is cleaved by trypsin-like proteases, including TMPRSS2 and HAT, whereas the multibasic motif found in high pathogenicity avian influenza HA is cleaved by furin, PC5/6, or MSPL. MSPL belongs to the TMPRSS family and preferentially cleaves [R/K]-K-K-R↓ sequences. Here, we solved the crystal structure of the extracellular region of human MSPL in complex with an irreversible substrate-analog inhibitor. The structure revealed three domains clustered around the C-terminal α-helix of the SPD. The inhibitor structure and its putative model show that the P1-Arg inserts into the S1 pocket, whereas the P2-Lys and P4-Arg interacts with the Asp/Glu-rich 99-loop that is unique to MSPL. Based on the structure of MSPL, we also constructed a homology model of TMPRSS2, which is essential for the activation of the SARS-CoV-2 spike protein and infection. The model may provide the structural insight for the drug development for COVID-19.

Hepsin: a multifunctional transmembrane serine protease in pathobiology

Cell membrane-bound serine proteases are important in the maintenance of physiological homeostasis. Hepsin is a type II transmembrane serine protease highly expressed in the liver. Recent studies indicate that hepsin activates prohepatocyte growth factor in the liver to enhance Met signaling, thereby regulating glucose, lipid, and protein metabolism. In addition, hepsin functions in nonhepatic tissues, including the adipose tissue, kidney, and inner ear, to regulate adipocyte differentiation, urinary protein processing, and auditory function, respectively. In mouse models, hepsin deficiency lowers blood glucose, lipid, and protein levels, impairs uromodulin assembly in renal epithelial cells, and causes hearing loss. Elevated hepsin expression has also been found in many cancers. As a type II transmembrane protease, cell surface expression and zymogen activation are essential for hepsin activity. In this review, we discuss the current knowledge regarding hepsin biosynthesis, activation, and functions in pathobiology.

Targeting Enteropeptidase with Reversible Covalent Inhibitors To Achieve Metabolic Benefits

Inhibition of the serine protease enteropeptidase (EP) opens a new avenue to the discovery of chemotherapeutics for the treatment of metabolic diseases. Camostat has been used clinically for treating chronic pancreatitis in Japan; however, the mechanistic basis of the observed clinical efficacy has not been fully elucidated. We demonstrate that camostat is a potent reversible covalent inhibitor of EP, with an inhibition potency (k inact/KI) of 1.5 × 104 M-1s-1 High-resolution liquid chromatography-mass spectrometry (LC-MS) showed addition of 161.6 Da to EP after the reaction with camostat, consistent with insertion of the carboxyphenylguanidine moiety of camostat. Covalent inhibition of EP by camostat is reversible, with an enzyme reactivation half-life of 14.3 hours. Formation of a covalent adduct was further supported by a crystal structure resolved to 2.19 Å, showing modification of the catalytic serine of EP by a close analog of camostat, leading to formation of the carboxyphenylguanidine acyl enzyme identical to that expected for the reaction with camostat. Of particular note, minor structural modifications of camostat led to changes in the mechanism of inhibition. We observed from other studies that sustained inhibition of EP is required to effect a reduction in cumulative food intake and body weight, with concomitant improved blood glucose levels in obese and diabetic leptin-deficient mice. Thus, the structure-activity relationship needs to be driven by not only the inhibition potency but also the mechanistic and kinetic characterization. Our findings support EP as a target for the treatment of metabolic diseases and demonstrate that reversible covalent EP inhibitors show clinically relevant efficacy. SIGNIFICANCE STATEMENT: Interest in targeted covalent drugs has expanded in recent years, particularly so for kinase targets, but also more broadly. This study demonstrates that reversible covalent inhibition of the serine protease enteropeptidase is a therapeutically viable approach to the treatment of metabolic diseases and that mechanistic details of inhibition are relevant to clinical efficacy. Our mechanistic and kinetic studies outline a framework for detailed inhibitor characterization that is proving essential in guiding discovery efforts in this area.

Novel Compound Heterozygous TMPRSS15 Gene Variants Cause Enterokinase Deficiency

Background

Enterokinase deficiency (EKD) is a rare autosomal recessively inherited disorder mainly characterized by diarrhea, hypoproteinemia and failure to thrive in infancy. Loss-of-function variants in the TMPRSS15 gene cause EKD.

Methods

We report the clinical manifestations and molecular basis of EKD in a Chinese child. We investigated in vitro two TMPRSS15 variants: the c.1921G > A as a possible splicing variant by minigene assay; the c.2396T > A(p.Val799Asp) as a missense change by protein expression analysis, enterokinase activity and effect on cellular localization.

Results

The proband presented with intractable diarrhea accompanied by vomiting, failure to thrive and hypoproteinemia in his second year. Genetic analysis showed that the patient was compound heterozygous for two variants in the TMPRSS15 gene: c.[1921G > A];[2396T > A]. The c.1921 G > A variant may change the glutamic acid 641 into lysine; this change is predicted to be benign by bioinformatics analysis. However, it was predicted to disrupt the splicing donor site. Our minigene assay revealed that c.1921G > A caused the skipping of exon 16. The c.2396T > A(p.Val799Asp) change in the serine protease domain predicted to be deleterious hitting an evolutionary conserved amino acid. Functional studies in vitro revealed that the p.Val799Asp variant decreased the total expression level of TMPRSS15 by 29%, and the enterokinase activity of p.Val799Asp mutants was decreased by 37%, compared with that of wild type.

Conclusion

We reported an EKD patient with novel compound heterozygous variants in the TMPRSS15 gene, expanding the genotypic and phenotypic spectrum of EKD. The functional characterization in vitro demonstrated that the c.1921G > A variant alters pre-mRNA splicing and the p.Val799Asp variant leads to a decrease in protein expression and enzyme activity.

Matriptase-2: monitoring and inhibiting its proteolytic activity

Matriptase-2 (MT2) is a membrane-anchored proteolytic enzyme. It acts as the proteolytic key regulator in human iron homeostasis. A high expression level can lead to iron overload diseases, whereas mutations in the gene encoding MT2, TMPRSS6, may result in various forms of iron deficiency anemia. Recently, MT2 has been reported as a positive prognostic factor in breast and prostate cancers. However, the exact functions of MT2 in various pathophysiological conditions are still not fully understood. In this review, we describe the synthetic tools designed and synthesized to regulate or monitor MT2 proteolytic activity and present the latest knowledge about the role of MT2 in iron homeostasis and cancer.

N-glycosylation in the protease domain of trypsin-like serine proteases mediates calnexin-assisted protein folding

Trypsin-like serine proteases are essential in physiological processes. Studies have shown that N-glycans are important for serine protease expression and secretion, but the underlying mechanisms are poorly understood. Here, we report a common mechanism of N-glycosylation in the protease domains of corin, enteropeptidase and prothrombin in calnexin-mediated glycoprotein folding and extracellular expression. This mechanism, which is independent of calreticulin and operates in a domain-autonomous manner, involves two steps: direct calnexin binding to target proteins and subsequent calnexin binding to monoglucosylated N-glycans. Elimination of N-glycosylation sites in the protease domains of corin, enteropeptidase and prothrombin inhibits corin and enteropeptidase cell surface expression and prothrombin secretion in transfected HEK293 cells. Similarly, knocking down calnexin expression in cultured cardiomyocytes and hepatocytes reduced corin cell surface expression and prothrombin secretion, respectively. Our results suggest that this may be a general mechanism in the trypsin-like serine proteases with N-glycosylation sites in their protease domains.

Membrane-Anchored Serine Proteases: Host Cell Factors in Proteolytic Activation of Viral Glycoproteins

Over one third of all known proteolytic enzymes are serine proteases. Among these, the trypsin-like serine proteases comprise one of the best characterized subfamilies due to their essential roles in blood coagulation, food digestion, fibrinolysis, or immunity. Trypsin-like serine proteases possess primary substrate specificity for basic amino acids. Most of the well-characterized trypsin-like proteases such as trypsin, plasmin, or urokinase are soluble proteases that are secreted into the extracellular environment. At the turn of the millennium, a number of novel trypsin-like serine proteases have been identified that are anchored in the cell membrane, either by a transmembrane domain at the N- or C-terminus or via a glycosylphosphatidylinositol (GPI) linkage. Meanwhile more than 20 membrane-anchored serine proteases (MASPs) have been identified in human and mouse, and some of them have emerged as key regulators of mammalian development and homeostasis. Thus, the MASP corin and TMPRSS6/matriptase-2 have been demonstrated to be the activators of the atrial natriuretic peptide (ANP) and key regulator of hepcidin expression, respectively. Furthermore, MASPs have been recognized as host cell factors activating respiratory viruses including influenza virus as well as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) coronaviruses. In particular, transmembrane protease serine S1 member 2 (TMPRSS2) has been shown to be essential for proteolytic activation and consequently spread and pathogenesis of a number of influenza A viruses in mice and as a factor associated with severe influenza virus infection in humans.

This review gives an overview on the physiological functions of the fascinating and rapidly evolving group of MASPs and a summary of the current knowledge on their role in proteolytic activation of viral fusion proteins.

TMPRSS2 and MSPL Facilitate Trypsin-Independent Porcine Epidemic Diarrhea Virus Replication in Vero Cells

Type II transmembrane serine proteases (TTSPs) facilitate the spread and replication of viruses such as influenza and human coronaviruses, although it remains unclear whether TTSPs play a role in the progression of animal coronavirus infections, such as that by porcine epidemic diarrhea virus (PEDV). In this study, TTSPs including TMPRSS2, HAT, DESC1, and MSPL were tested for their ability to facilitate PEDV replication in Vero cells. Our results showed that TMPRSS2 and MSPL played significant roles in the stages of cell-cell fusion and virus-cell fusion, whereas HAT and DESC1 exhibited weaker effects. This activation may be involved in the interaction between TTSPs and the PEDV S protein, as the S protein extensively co-localized with TMPRSS2 and MSPL and could be cleaved by co-expression with TMPRSS2 or MSPL. Moreover, the use of Vero cells expressing TMPRSS2 and MSPL facilitated PEDV replication in the absence of exogenous trypsin. In sum, we identified two host proteases, TMPRSS2 and MSPL, which may provide insights and a novel method for enhancing viral titers, expanding virus production, and improving the adaptability of PEDV isolates in vitro.

Serum Trypsinogen Levels in Type 1 Diabetes

OBJECTIVE

The pancreas in type 1 diabetes exhibits decreased size (weight/volume) and abnormal exocrine morphology. Serum trypsinogen levels are an established marker of pancreatic exocrine function. As such, we hypothesized that trypsinogen levels may be reduced in patients with pre-type 1 diabetes and type 1 diabetes compared with healthy control subjects.

RESEARCH DESIGN AND METHODS

Serum trypsinogen levels were determined in 100 persons with type 1 diabetes (72 new-onset, 28 established), 99 autoantibody-positive (AAb+) subjects at varying levels of risk for developing this disease, 87 AAb-negative (AAb-) control subjects, 91 AAb- relatives with type 1 diabetes, and 18 patients with type 2 diabetes.

RESULTS

Trypsinogen levels increased significantly with age in control subjects (r = 0.71; P < 0.0001) and were significantly lower in patients with new-onset (mean ± SD 14.5 ± 6.1 ng/mL; P < 0.0001) and established type 1 diabetes (16.7 ± 6.9 ng/mL; P < 0.05) versus AAb- control subjects (25.3 ± 11.2 ng/mL), AAb- relatives (29.3 ± 15.0 ng/mL), AAb+ subjects (26.5 ± 12.1 ng/mL), and patients with type 2 diabetes (31.5 ± 17.3 ng/mL). Multivariate analysis revealed reduced trypsinogen in multiple-AAb+ subjects (P < 0.05) and patients with type 1 diabetes (P < 0.0001) compared with AAb- subjects (control subjects and relatives combined) and single-AAb+ (P < 0.01) subjects when considering age and BMI.

CONCLUSIONS

These findings further support the interplay between pancreatic endocrine and exocrine dysfunction. Longitudinal studies are warranted to validate trypsinogen as a predictive biomarker of type 1 diabetes progression.

Extracellular: Plasma Membrane Proteases – Serine Proteases

Membrane-anchored serine proteases are a group of extracellular serine proteases tethered directly to plasma membranes, via a C-terminal glycosylphosphatidylinositol linkage (GPI-anchored), a C-terminal transmembrane domain (Type I), or an N-terminal transmembrane domain (Type II). A variety of biochemical, cellular, and in vivo studies have established that these proteases are important pericellular contributors to processes vital for the maintenance of homeostasis, including food digestion, blood pressure regulation, hearing, epithelial permeability, sperm maturation, and iron homeostasis. These enzymes are hijacked by viruses to facilitate infection and propagation, and their misregulation is associated with a wide range of diseases, including cancer malignancy.

Propeptides as modulators of functional activity of proteases

Most proteases are synthesized in the cell as precursor-containing propeptides. These structural elements can determine the folding of the cognate protein, function as an inhibitor/activator peptide, mediate enzyme sorting, and mediate the protease interaction with other molecules and supramolecular structures. The data presented in this review demonstrate modulatory activity of propeptides irrespective of the specific mechanism of action. Changes in propeptide structure, sometimes minor, can crucially alter protein function in the living organism. Modulatory activity coupled with high variation allows us to consider propeptides as specific evolutionary modules that can transform biological properties of proteases without significant changes in the highly conserved catalytic domains. As the considered properties of propeptides are not unique to proteases, propeptide-mediated evolution seems to be a universal biological mechanism.

Digestive peptidase evolution in holometabolous insects led to a divergent group of enzymes in Lepidoptera

Trypsins and chymotrypsins are well-studied serine peptidases that cleave peptide bonds at the carboxyl side of basic and hydrophobic L-amino acids, respectively. These enzymes are largely responsible for the digestion of proteins. Three primary processes regulate the activity of these peptidases: secretion, precursor (zymogen) activation and substrate-binding site recognition. Here, we present a detailed phylogenetic analysis of trypsins and chymotrypsins in three orders of holometabolous insects and reveal divergent characteristics of Lepidoptera enzymes in comparison with those of Coleoptera and Diptera. In particular, trypsin subsite S1 was more hydrophilic in Lepidoptera than in Coleoptera and Diptera, whereas subsites S2-S4 were more hydrophobic, suggesting different substrate preferences. Furthermore, Lepidoptera displayed a lineage-specific trypsin group belonging only to the Noctuidae family. Evidence for facilitated trypsin auto-activation events were also observed in all the insect orders studied, with the characteristic zymogen activation motif complementary to the trypsin active site. In contrast, insect chymotrypsins did not seem to have a peculiar evolutionary history with respect to their mammal counterparts. Overall, our findings suggest that the need for fast digestion allowed holometabolous insects to evolve divergent groups of peptidases with high auto-activation rates, and highlight that the evolution of trypsins led to a most diverse group of enzymes in Lepidoptera.

Myoinhibitory peptide regulates feeding in the marine annelid Platynereis

Background

During larval settlement and metamorphosis, marine invertebrates undergo changes in habitat, morphology, behavior and physiology. This change between life-cycle stages is often associated with a change in diet or a transition between a non-feeding and a feeding form. How larvae regulate changes in feeding during this life-cycle transition is not well understood. Neuropeptides are known to regulate several aspects of feeding, such as food search, ingestion and digestion. The marine annelid Platynereis dumerilii has a complex life cycle with a pelagic non-feeding larval stage and a benthic feeding postlarval stage, linked by the process of settlement. The conserved neuropeptide myoinhibitory peptide (MIP) is a key regulator of larval settlement behavior in Platynereis. Whether MIP also regulates the initiation of feeding, another aspect of the pelagic-to-benthic transition in Platynereis, is currently unknown.

Results

Here, we explore the contribution of MIP to the regulation of feeding behavior in settled Platynereis postlarvae. We find that in addition to expression in the brain, MIP is expressed in the gut of developing larvae in sensory neurons that densely innervate the hindgut, the foregut, and the midgut. Activating MIP signaling by synthetic neuropeptide addition causes increased gut peristalsis and more frequent pharynx extensions leading to increased food intake. Conversely, morpholino-mediated knockdown of MIP expression inhibits feeding. In the long-term, treatment of Platynereis postlarvae with synthetic MIP increases growth rate and results in earlier cephalic metamorphosis.

Conclusions

Our results show that MIP activates ingestion and gut peristalsis in Platynereis postlarvae. MIP is expressed in enteroendocrine cells of the digestive system suggesting that following larval settlement, feeding may be initiated by a direct sensory-neurosecretory mechanism. This is similar to the mechanism by which MIP induces larval settlement. The pleiotropic roles of MIP may thus have evolved by redeploying the same signaling mechanism in different aspects of a life-cycle transition.

Electronic supplementary material

The online version of this article (doi:10.1186/s12983-014-0093-6) contains supplementary material, which is available to authorized users.

Drug-induced acute pancreatitis: a review

BACKGROUND

The majority of drug-induced pancreatitis cases are mild to moderate in severity, but severe and even fatal cases can occur. Management of drug-induced pancreatitis requires withdrawal of the offending agent and supportive care.

METHODS

This review focuses on differential diagnosis, clinical presentation, drug-mediated effects, treatments, and mechanisms of pancreatitis, with an emphasis on drug-induced pancreatitis.

RESULTS

Although only a minority of cases associated with acute pancreatitis are linked to drugs, clinical presentation and mechanisms of injury to the pancreas are not well understood by clinicians in terms of individual drug effects in the mediation or modulation of injury to the pancreas. In recent years, a large number of commonly prescribed medications has been linked to drug-induced pancreatitis pathogenesis. Although mechanisms are proposed, the exact cause of injury is either not well understood or controversial.

CONCLUSION

Future investigation into the mechanisms of pancreatitis and an appreciation by clinicians of the drugs commonly linked to the condition will help establish earlier diagnosis and quicker cessation of offending drugs in the treatment of drug-induced acute pancreatitis.

Distinct roles of N-glycosylation at different sites of corin in cell membrane targeting and ectodomain shedding

Corin is a membrane-bound protease essential for activating natriuretic peptides and regulating blood pressure. Human corin has 19 predicted N-glycosylation sites in its extracellular domains. It has been shown that N-glycans are required for corin cell surface expression and zymogen activation. It remains unknown, however, how N-glycans at different sites may regulate corin biosynthesis and processing. In this study, we examined corin mutants, in which each of the 19 predicted N-glycosylation sites was mutated individually. By Western analysis of corin proteins in cell lysate and conditioned medium from transfected HEK293 cells and HL-1 cardiomyocytes, we found that N-glycosylation at Asn-80 inhibited corin shedding in the juxtamembrane domain. Similarly, N-glycosylation at Asn-231 protected corin from autocleavage in the frizzled-1 domain. Moreover, N-glycosylation at Asn-697 in the scavenger receptor domain and at Asn-1022 in the protease domain is important for corin cell surface targeting and zymogen activation. We also found that the location of the N-glycosylation site in the protease domain was not critical. N-Glycosylation at Asn-1022 may be switched to different sites to promote corin zymogen activation. Together, our results show that N-glycans at different sites may play distinct roles in regulating the cell membrane targeting, zymogen activation, and ectodomain shedding of corin.

Cleavage specificity analysis of six type II transmembrane serine proteases (TTSPs) using PICS with proteome-derived peptide libraries

Background

Type II transmembrane serine proteases (TTSPs) are a family of cell membrane tethered serine proteases with unclear roles as their cleavage site specificities and substrate degradomes have not been fully elucidated. Indeed just 52 cleavage sites are annotated in MEROPS, the database of proteases, their substrates and inhibitors.

Methodology/Principal Finding

To profile the active site specificities of the TTSPs, we applied Proteomic Identification of protease Cleavage Sites (PICS). Human proteome-derived database searchable peptide libraries were assayed with six human TTSPs (matriptase, matriptase-2, matriptase-3, HAT, DESC and hepsin) to simultaneously determine sequence preferences on the N-terminal non-prime (P) and C-terminal prime (P’) sides of the scissile bond. Prime-side cleavage products were isolated following biotinylation and identified by tandem mass spectrometry. The corresponding non-prime side sequences were derived from human proteome databases using bioinformatics. Sequencing of 2,405 individual cleaved peptides allowed for the development of the family consensus protease cleavage site specificity revealing a strong specificity for arginine in the P1 position and surprisingly a lysine in P1′ position. TTSP cleavage between R↓K was confirmed using synthetic peptides. By parsing through known substrates and known structures of TTSP catalytic domains, and by modeling the remainder, structural explanations for this strong specificity were derived.

Conclusions

Degradomics analysis of 2,405 cleavage sites revealed a similar and characteristic TTSP family specificity at the P1 and P1′ positions for arginine and lysine in unfolded peptides. The prime side is important for cleavage specificity, thus making these proteases unusual within the tryptic-enzyme class that generally has overriding non-prime side specificity.

Membrane Proteins Involved in Epithelial-Mesenchymal Transition and Tumor Invasion: Studies on TMPRSS4 and TM4SF5

The epithelial-mesenchymal transition (EMT) is one mechanism by which cells with mesenchymal features can be generated and is a fundamental event in morphogenesis. Recently, invasion and metastasis of cancer cells from the primary tumor are now thought to be initiated by the developmental process termed the EMT, whereby epithelial cells lose cell polarity and cell-cell interactions, and gain mesenchymal phenotypes with increased migratory and invasive properties. The EMT is believed to be an important step in metastasis and is implicated in cancer progression, although the influence of the EMT in clinical specimens has been debated. This review presents the recent results of two cell surface proteins, the functions and underlying mechanisms of which have recently begun to be demonstrated, as novel regulators of the molecular networks that induce the EMT and cancer progression.

Serine proteases of small intestine mucosa--localization, functional properties, and physiological role

In this review we present data about small intestine serine proteases, which are a considerable part of the proteolytic apparatus in this major part of the gastrointestinal tract. Serine proteases of intestinal epitheliocytes, their structural-functional features, cellular localization, physiological substrates, and mechanisms of activity regulation are examined. Information about biochemical and functional properties of serine proteases is presented in a common context with morphological and physiological data, this being the basis for understanding the functional processes taking place in upper part of the intestine. Serine proteases play a key role in the physiology of the small intestine and provide the normal functioning of this organ as part of the digestive system in which hydrolysis and suction of food substances occur. They participate in renewal and remodeling of tissues, retractive activity of smooth musculature, hormonal regulation, and defense mechanisms of the intestine.

Pyrosequencing of Haliotis diversicolor transcriptomes: insights into early developmental molluscan gene expression

Background

The abalone Haliotis diversicolor is a good model for study of the settlement and metamorphosis, which are widespread marine ecological phenomena. However, information on the global gene backgrounds and gene expression profiles for the early development of abalones is lacking.

Methodology/Principal Findings

In this study, eight non-normalized and multiplex barcode-labeled transcriptomes were sequenced using a 454 GS system to cover the early developmental stages of the abalone H. diversicolor. The assembly generated 35,415 unigenes, of which 7,566 were assigned GO terms. A global gene expression profile containing 636 scaffolds/contigs was constructed and was proven reliable using qPCR evaluation. It indicated that there may be existing dramatic phase transitions. Bioprocesses were proposed, including the ‘lock system’ in mature eggs, the collagen shells of the trochophore larvae and the development of chambered extracellular matrix (ECM) structures within the earliest postlarvae.

Conclusion

This study globally details the first 454 sequencing data for larval stages of H. diversicolor. A basic analysis of the larval transcriptomes and cluster of the gene expression profile indicates that each stage possesses a batch of specific genes that are indispensable during embryonic development, especially during the two-cell, trochophore and early postlarval stages. These data will provide a fundamental resource for future physiological works on abalones, revealing the mechanisms of settlement and metamorphosis at the molecular level.

Phylogenetic identification of bacterial MazF toxin protein motifs among probiotic strains and foodborne pathogens and potential implications of engineered probiotic intervention in food

BACKGROUND

Toxin-antitoxin (TA) systems are commonly found in bacteria and Archaea, and it is the most common mechanism involved in bacterial programmed cell death or apoptosis. Recently, MazF, the toxin component of the toxin-antitoxin module, has been categorized as an endoribonuclease, or it may have a function similar to that of a RNA interference enzyme.

RESULTS

In this paper, with comparative data and phylogenetic analyses, we are able to identify several potential MazF-conserved motifs in limited subsets of foodborne pathogens and probiotic strains and further provide a molecular basis for the development of engineered/synthetic probiotic strains for the mitigation of foodborne illnesses. Our findings also show that some probiotic strains, as fit as many bacterial foodborne pathogens, can be genetically categorized into three major groups based on phylogenetic analysis of MazF. In each group, potential functional motifs are conserved in phylogenetically distant species, including foodborne pathogens and probiotic strains.

CONCLUSION

These data provide important knowledge for the identification and computational prediction of functional motifs related to programmed cell death. Potential implications of these findings include the use of engineered probiotic interventions in food or use of a natural probiotic cocktail with specificity for controlling targeted foodborne pathogens.

Enteropeptidase: a gene associated with a starvation human phenotype and a novel target for obesity treatment

Background

Obesity research focuses essentially on gene targets associated with the obese phenotype. None of these targets have yet provided a viable drug therapy. Focusing instead on genes that are involved in energy absorption and that are associated with a “human starvation phenotype”, we have identified enteropeptidase (EP), a gene associated with congenital enteropeptidase deficiency, as a novel target for obesity treatment. The advantages of this target are that the gene is expressed exclusively in the brush border of the intestine; it is peripheral and not redundant.

Methodology/Principal Findings

Potent and selective EP inhibitors were designed around a boroarginine or borolysine motif. Oral administration of these compounds to mice restricted the bioavailability of dietary energy, and in a long-term treatment it significantly diminished the rate of increase in body weight, despite ad libitum food intake. No adverse reactions of the type seen with lipase inhibitors, such as diarrhea or steatorrhea, were observed. This validates EP as a novel, druggable target for obesity treatment.

Conclusions

In vivo testing of novel boroarginine or borolysine-based EP inhibitors validates a novel approach to the treatment of obesity.

The conserved scavenger receptor cysteine-rich superfamily in therapy and diagnosis

The scavenger receptor cysteine-rich (SRCR) superfamily of soluble or membrane-bound protein receptors is characterized by the presence of one or several repeats of an ancient and highly conserved protein module, the SRCR domain. This superfamily (SRCR-SF) has been in constant and progressive expansion, now up to more than 30 members. The study of these members is attracting growing interest, which parallels that in innate immunity. No unifying function has been described to date for the SRCR domains, this being the result of the limited knowledge still available on the physiology of most members of the SRCR-SF, but also of the sequence versatility of the SRCR domains. Indeed, involvement of SRCR-SF members in quite different functions, such as pathogen recognition, modulation of the immune response, epithelial homeostasis, stem cell biology, and tumor development, have all been described. This has brought to us new information, unveiling the possibility that targeting or supplementing SRCR-SF proteins could result in diagnostic and/or therapeutic benefit for a number of physiologic and pathologic states. Recent research has provided structural and functional insight into these proteins, facilitating the development of means to modulate the activity of SRCR-SF members. Indeed, some of these approaches are already in use, paving the way for a more comprehensive use of SRCR-SF members in the clinic. The present review will illustrate some available evidence on the potential of well known and new members of the SRCR-SF in this regard.

Corin in clinical laboratory diagnostics

Corin is a transmembrane serine protease identified in the heart, where it converts natriuretic peptides from inactive precursors to mature active forms. Studies in animal models and patients with hypertension and heart disease demonstrate that corin is critical in maintaining normal blood pressure and cardiac function. Like many proteolytic enzymes, corin expression and activity are regulated. Cell biology experiments indicate that transcriptional control, intracellular protein trafficking, cell surface targeting, zymogen activation and ectodomain shedding are important mechanisms in regulating corin expression and activity in the heart. More recently, soluble corin was detected in human blood and its levels were found to be reduced in patients with heart failure (HF). These findings indicate that corin deficiency may be involved in the pathogenesis of HF and suggest that soluble corin may be used as a biomarker for the disease. In this review, we describe the function and regulation of corin and discuss recent studies of soluble corin in human blood and its potential use as a biomarker for HF.

Membrane-anchored serine proteases in health and disease

Serine proteases of the trypsin-like family have long been recognized to be critical effectors of biological processes as diverse as digestion, blood coagulation, fibrinolysis, and immunity. In recent years, a subgroup of these enzymes has been identified that are anchored directly to plasma membranes, either by a carboxy-terminal transmembrane domain (Type I), an amino-terminal transmembrane domain with a cytoplasmic extension (Type II or TTSP), or through a glycosylphosphatidylinositol (GPI) linkage. Recent biochemical, cellular, and in vivo analyses have now established that membrane-anchored serine proteases are key pericellular contributors to processes vital for development and the maintenance of homeostasis. This chapter reviews our current knowledge of the biological and physiological functions of these proteases, their molecular substrates, and their contributions to disease.

'Energy expenditure genes' or 'energy absorption genes': a new target for the treatment of obesity and Type II diabetes

Several hundred genes associated or linked to obesity have been described in the scientific literature. Whereas many of these genes are potential targets for the treatment of obesity and associated conditions, none of them have permitted the developement of an efficient drug therapy. As proposed by the 'thrifty genotype' theory, obesity genes may have conferred an evolutionary advantage in times of food shortage through efficient energy exploitation, while 'lean' or 'energy expenditure' genes may have become very rare during the same periods. It is therefore a challenge to identify 'energy expenditure genes' or 'energy absorption genes,' whose mutations or single nucleotide polymorphisms do result in reduced energy intake. We submit that such 'energy absorption' or 'energy expenditure' genes (crucial genes) are potential new targets for the treatment of obesity. These genes can be identified in rare genetic diseases that produce a lean, failure-to-thrive, energy malabsorption or starvation phenotype.

Pre-expression of a sulfhydryl oxidase significantly increases the yields of eukaryotic disulfide bond containing proteins expressed in the cytoplasm of E.coli

Background

Disulfide bonds are one of the most common post-translational modifications found in proteins. The production of proteins that contain native disulfide bonds is challenging, especially on a large scale. Either the protein needs to be targeted to the endoplasmic reticulum in eukaryotes or to the prokaryotic periplasm. These compartments that are specialised for disulfide bond formation have an active catalyst for their formation, along with catalysts for isomerization to the native state. We have recently shown that it is possible to produce large amounts of prokaryotic disulfide bond containing proteins in the cytoplasm of wild-type bacteria such as E. coli by the introduction of catalysts for both of these processes.

Results

Here we show that the introduction of Erv1p, a sulfhydryl oxidase and a disulfide isomerase allows the efficient formation of natively folded eukaryotic proteins with multiple disulfide bonds in the cytoplasm of E. coli. The production of disulfide bonded proteins was also aided by the use of an appropriate fusion protein to keep the folding intermediates soluble and by choice of media. By combining the pre-expression of a sulfhydryl oxidase and a disulfide isomerase with these other factors, high level expression of even complex disulfide bonded eukaryotic proteins is possible

Conclusions

Our results show that the production of eukaryotic proteins with multiple disulfide bonds in the cytoplasm of E. coli is possible. The required exogenous components can be put onto a single plasmid vector allowing facile transfer between different prokaryotic strains. These results open up new avenues for the use of E. coli as a microbial cell factory.