cDNA sequence and chromosomal localization of human enterokinase, the proteolytic activator of trypsinogen

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.

MMR vaccination induces trained immunity via functional and metabolic reprogramming of γδ T cells

The measles, mumps, and rubella (MMR) vaccine protects against all-cause mortality in children, but the immunological mechanisms mediating these effects are poorly known. We systematically investigated whether MMR can induce long-term functional changes in innate immune cells, a process termed trained immunity, that could at least partially mediate this heterologous protection. In a randomized, placebo-controlled trial, 39 healthy adults received either the MMR vaccine or a placebo. Using single-cell RNA-Seq, we found that MMR caused transcriptomic changes in CD14+ monocytes and NK cells, but most profoundly in γδ T cells. Monocyte function was not altered by MMR vaccination. In contrast, the function of γδ T cells was markedly enhanced by MMR vaccination, with higher production of TNF and IFN-γ, as well as upregulation of cellular metabolic pathways. In conclusion, we describe a trained immunity program characterized by modulation of γδ T cell function induced by MMR vaccination.

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.

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/K_I) 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.

Enterokinase Enhances Influenza A Virus Infection by Activating Trypsinogen in Human Cell Lines

Cleavage and activation of hemagglutinin (HA) by trypsin-like proteases in influenza A virus (IAV) are essential prerequisites for its successful infection and spread. In host cells, some transmembrane serine proteases such as TMPRSS2, TMPRSS4 and HAT, along with plasmin in the bloodstream, have been reported to cleave the HA precursor (HA₀) molecule into its active forms, HA₁ and HA₂. Some trypsinogens can also enhance IAV proliferation in some cell types (e.g., rat cardiomyoblasts). However, the precise activation mechanism for this process is unclear, because the expression level of the physiological activator of the trypsinogens, the TMPRSS15 enterokinase, is expected to be very low in such cells, with the exception of duodenal cells. Here, we show that at least two variant enterokinases are expressed in various human cell lines, including A549 lung-derived cells. The exogenous expression of these enterokinases was able to enhance the proliferation of IAV in 293T human kidney cells, but the proliferation was reduced by knocking down the endogenous enterokinase in A549 cells. The enterokinase was able to enhance HA processing in the cells, which activated trypsinogen in vitro and in the IAV-infected cells also. Therefore, we conclude that enterokinase plays a role in IAV infection and proliferation by activating trypsinogen to process viral HA in human cell lines.

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.

Human airway trypsin-like protease, a serine protease involved in respiratory diseases

More than 2% of all human genes are coding for a complex system of more than 700 proteases and protease inhibitors. Among them, serine proteases play extraordinary, diverse functions in different physiological and pathological processes. The human airway trypsin-like protease (HAT), also referred to as TMPRSS11D and serine 11D, belongs to the emerging family of cell surface proteolytic enzymes, the type II transmembrane serine proteases (TTSPs). Through the cleavage of its four major identified substrates, HAT triggers specific responses, notably in epithelial cells, within the pericellular and extracellular environment, including notably inflammatory cytokine production, inflammatory cell recruitment, or anticoagulant processes. This review summarizes the potential role of this recently described protease in mediating cell surface proteolytic events, to highlight the structural features, proteolytic activity, and regulation, including the expression profile of HAT, and discuss its possible roles in respiratory physiology and disease.

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.

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.

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.

Effect of enteropeptidase on survival of cultured hippocampal neurons under conditions of glutamate toxicity

The effects of full-size bovine enteropeptidase (BEK) and of human recombinant light chain enteropeptidase (L-HEP) on survival of cultured hippocampal neurons were studied under conditions of glutamate excitotoxicity. Low concentrations of L-HEP or BEK (0.1-1 and 0.1-0.5 nM, respectively) protected hippocampal neurons against the death caused by 100 µM glutamate. Using the PAR1 (proteinase-activated receptor) antagonist SCH 79797, we revealed a PAR1-dependent mechanism of neuroprotective action of low concentrations of enteropeptidase. The protective effect of full-size enteropeptidase was not observed at the concentrations of 1 and 10 nM; moreover, 10 nM of BEK caused death of 88.9% of the neurons, which significantly exceeded the cell death caused by glutamate (31.9%). Under conditions of glutamate cytotoxicity the survival of neurons was 26.8% higher even in the presence of 10 nM of L-HEP than in the presence of 10 nM BEK. Pretreatment of cells with 10 nM of either form of enteropeptidase abolished the protective effect of 10 nM thrombin under glutamate cytotoxicity. High concentrations of BEK and L-HEP caused the death of neurons mainly through necrosis.

Surface supercharged human enteropeptidase light chain shows improved solubility and refolding yield

Enteropeptidase is a serine protease used in different biotechnological applications. For many applications the smaller light chain can be used to avoid the expression of the rather large holoenzyme. Recombinant human enteropeptidase light chain (hEPL) shows high activity but low solubility and refolding yields, currently limiting its use in biotechnological applications. Here we describe several protein modifications that lead to improved solubility and refolding yield of human hEPL whilst retaining the enzyme activity. Specifically, protein surface supercharging (N6D, G21D, G22D, N141D, K209E) of the protein increased the solubility more than 100-fold. Replacement of a free cysteine residue with serine (C112S) improved the refolding yield by 50%. The heat stability of this C112S variant was also significantly improved by supercharging. This study shows that even mild protein surface supercharging can have pronounced effects on protein solubility and stability.

Proteolytic processing of the serine protease matriptase-2: identification of the cleavage sites required for its autocatalytic release from the cell surface

Matriptase-2 is a member of the TTSPs (type II transmembrane serine proteases), an emerging class of cell surface proteases involved in tissue homoeostasis and several human disorders. Matriptase-2 exhibits a domain organization similar to other TTSPs, with a cytoplasmic N-terminus, a transmembrane domain and an extracellular C-terminus containing the non-catalytic stem region and the protease domain. To gain further insight into the biochemical functions of matriptase-2, we characterized the subcellular localization of the monomeric and multimeric form and identified cell surface shedding as a defining point in its proteolytic processing. Using HEK (human embryonic kidney)-293 cells, stably transfected with cDNA encoding human matriptase-2, we demonstrate a cell membrane localization for the inactive single-chain zymogen. Membrane-associated matriptase-2 is highly N-glycosylated and occurs in monomeric, as well as multimeric, forms covalently linked by disulfide bonds. Furthermore, matriptase-2 undergoes shedding into the conditioned medium as an activated two-chain form containing the catalytic domain, which is cleaved at the canonical activation motif, but is linked to a released portion of the stem region via a conserved disulfide bond. Cleavage sites were identified by MS, sequencing and mutational analysis. Interestingly, cell surface shedding and activation of a matriptase-2 variant bearing a mutation at the active-site serine residue is dependent on the catalytic activity of co-expressed or co-incubated wild-type matriptase-2, indicating a transactivation and trans-shedding mechanism.

Roles and regulation of membrane-associated serine proteases

Pericellular proteolytic activity affects many aspects of cellular behaviour, via mechanisms involving processing of the extracellular matrix, growth factors and receptors. The serine proteases have exquisitely sensitive regulatory mechanisms in this setting, involving both receptor-bound and transmembrane proteases. Receptor-bound proteases are exemplified by the uPA (urokinase plasminogen activator)/uPAR (uPAR receptor) plasminogen activation system. The mechanisms initiating the activity of this proteolytic system on the cell surface, a critical regulatory point, are poorly understood. We have found that the expression of the TTSP (type II transmembrane serine protease) matriptase is highly regulated in leucocytes, and correlates with the presence of active uPA on their surface. Using siRNA (small interfering RNA), we have demonstrated that matriptase specifically activates uPAR-associated pro-uPA. The uPA/uPAR system has been implicated in the activation of the plasminogen-related growth factor HGF (hepatocyte growth factor). However, we find no evidence for this, but instead that HGF can be activated by both matriptase and the related TTSP hepsin in purified systems. Hepsin is of particular interest, as the proteolytic cleavage sequence of HGF is an 'ideal substrate' for hepsin and membrane-associated hepsin activates HGF with high efficiency. Both of these TTSPs can be activated autocatalytically at the cell surface, an unusual mechanism among the serine proteases. Therefore these TTSPs have the capacity to be true upstream initiators of proteolytic activity with subsequent downstream effects on cell behaviour.

Matriptase-2 Inhibits Breast Tumor Growth and Invasion and Correlates with Favorable Prognosis for Breast Cancer Patients

PURPOSE

The type II transmembrane serine proteases are cell surface proteolytic enzymes that mediate a diverse range of cellular functions, including tumor invasion and metastasis. Matriptase (matriptase-1) and matriptase-2 belong to the type II transmembrane serine protease family. Matriptase-1 is known to play a role in breast cancer progression, and elevated levels of matriptase-1 correlate with poor patient outcome. The role of matriptase-2 and its cellular function in cancer is unknown. This study aimed to provide new insights into the significance of matriptase-2 in cancer.

EXPERIMENTAL DESIGN

Matriptase-2 expression levels were assessed in a cohort of human breast cancer specimens (normal, n = 34; cancer, n = 95), in association with patient clinical variables, using both quantitative and qualitative analysis of the matriptase-2 transcript along with immunohistochemical techniques. Matriptase-2 was also experimentally overexpressed in the MDA-MB-231 human breast cancer cell line. The effects of matriptase-2 overexpression were examined through a series of in vitro and in vivo studies.

RESULTS

Here, we show that reduced matriptase-2 levels in breast cancer tissues correlate with an overall poor prognosis for the breast cancer patient. This study also reveals that matriptase-2 overexpression in breast cancer cells significantly suppressed tumorigenesis in CD1 athymic mice (P = 0.000003). Furthermore, we report that matriptase-2 overexpression dramatically reduced the invasive (P = 0.0001) and migratory properties (P = 0.01) of the breast cancer cells.

CONCLUSIONS

Matriptase-2 suppresses breast tumor development in vivo, displays prognostic value for breast cancer patients, inhibits both breast cancer cell invasion and motility in vitro, and may play a contrasting role to matriptase-1 in breast cancer.

Specificity of the medaka enteropeptidase serine protease and its usefulness as a biotechnological tool for fusion-protein cleavage

We cloned two distinct cDNAs for enteropeptidase (EP) from the intestine of the medaka, Oryzias latipes, which is a small freshwater teleost. The mRNAs code for EP-1 (1,036 residues) and EP-2 (1,043 residues), both of which have a unique, conserved domain structure of the N-terminal heavy chain and C-terminal catalytic serine protease light chain. When compared with mammalian EP serine proteases, the medaka enzyme exhibited extremely low amidolytic activity for small synthetic peptide substrates. Twelve mutated forms of the medaka EP protease were produced by site-directed mutagenesis. Among them, one mutant protease, E173A, was found to have considerably reduced nonspecific hydrolytic activities both for synthetic and protein substrates without serious reduction of its Asp-Asp-Asp-Asp-Lys (D(4)K)-cleavage activity. For the cleavage of fusion proteins containing a D(4)K-cleavage site, the medaka EP proteases were shown to have advantages over their mammalian counterparts. Based on our present data, we propose that the E173A mutant is the most appropriate protease to specifically cleave proteins containing the D(4)K cleavage sequence.

Proteins interacting with the ascidian vitelline-coat sperm receptor HrVC70 as revealed by yeast two-hybrid screening

Ascidians are hermaphrodites releasing sperm and eggs nearly simultaneously, but many species are self sterile. We have previously reported that HrVC70 consisting of 12 EGF-like repeats is a major component of the vitelline coat, functioning as a self/nonself-recognizable sperm receptor during fertilization of the ascidian Halocynthia roretzi. Here, in order to identify the binding partner of HrVC70, we explored HrVC70-interacting proteins by yeast two-hybrid screening. HrVC70 is capable of interacting with HrVC70 precursor HrVC120 itself and also with three additional extracellular and/or transmembrane proteins, HrVLP-1, -2, and HrTTSP-1. Specific interaction of HrVC120, HrVLP-1, -2, and HrTTSP-1 with HrVC70 was confirmed by exchanging prey and bait, and also by a pulldown assay using the GST-fusion proteins. HrVLP-1 and -2 are proteins structurally related to HrVC120; both are expressed in the oocytes and may be novel components of the ascidian vitelline coat. HrTTSP-1 appears to be a member of the serine protease family with type II transmembrane topology. HrTTSP-1 is expressed in the testis and its gene product contains multiple conserved motifs known to be involved in protein-protein or protein-carbohydrate interactions. Close inspection revealed that the protease domain of HrTTSP-1 is considerably divergent, in particular around the region of the catalytic center Ser residue. Possible roles of these proteins in ascidian fertilization are also discussed.

Serase-1B, a new splice variant of polyserase-1/TMPRSS9, activates urokinase-type plasminogen activator and the proteolytic activation is negatively regulated by glycosaminoglycans

Polyserase-1 (polyserine protease-1)/TMPRSS9 (transmembrane serine protease 9) is a type II transmembrane serine protease (TTSP) that possesses unique three tandem serine protease domains. However, the physiological function of each protease domain remains poorly understood. We discovered a new splice variant of polyserase-1, termed Serase-1B, which contains 34 extra amino acids consisting a SEA module (a domain found in sea urchin sperm protein, enterokinase and agrin) adjacent to the transmembrane domain and the first protease domain with a mucin-like box at the C-terminus. The tissue distribution of this enzyme by RT (reverse transcription)-PCR analysis revealed high expression in the liver, small intestine, pancreas, testis and peripheral blood CD14+ and CD8+ cells. To investigate the role of Serase-1B, a full-length form recombinant protein was produced. Interestingly, recombinant Serase-1B was partly secreted as a soluble inactive precursor and it was also activated by trypsin. This activated enzyme selectively cleaved synthetic peptides for trypsin and activated protein C, and it was inhibited by several natural serine protease inhibitors, such as aprotinin, alpha2-antiplasmin and plasminogen activator inhibitor 1. In addition, Serase-1B efficiently converted pro-uPA (urokinase-type plasminogen activator) into active uPA and this activation was strongly inhibited by these natural inhibitors. Furthermore, this activation was also negatively regulated by glycosaminoglycans. Our results indicate that Serase-1B is a novel member of TTSPs that might be involved in uPA/plasmin-mediated proteolysis and possibly implicated in biological events such as fibrinolysis and tumour progression.

Identification and characterization of hepsin/-TM, a non-transmembrane hepsin isoform

Type II transmembrane serine proteases (TTSPs), including hepsin, are a new class of cell surface catalytic enzymes. In the present study, a non-transmembrane isoform of hepsin, named hepsin/-TM that originates from alternative splicing, was identified. Unlike the transmembrane hepsin isoform, this non-transmembrane isoform was distributed within the cytoplasm. Real-time PCR experiments revealed that while hepsin was expressed in all tested human tissues, hepsin/-TM was restricted in kidney, brain and lung tissues. Significantly, hepsin/-TM was not expressed in liver where hepsin was originally identified. However, hepsin/-TM was highly expressed in brain where hepsin was expressed at a relatively lower level. Moreover, these two isoforms showed different expression patterns in a number of colon adenocarcinoma cell lines. In addition, in contrast to hepsin, expression of hepsin/-TM in vivo does not exert any apparent inhibitory effect on mammalian cell growth.

Expression of enteropeptidase in differentiated enterocytes, goblet cells, and the tumor cells in human duodenum

Enteropeptidase (EP) is a serine proteinase and activates trypsinogen to trypsin, thus playing an important role in food digestion. Nevertheless, the localization of EP is still controversial, likely due to a lack of studies using specific antibodies against EP. The aim of this study was to define cellular localization of EP in human duodenum and expression in tumor cells at the duodenal region. Immunohistochemical staining for resected tissues was performed with two antibodies against recombinant EP light and heavy chains, respectively. In situ hybridization was done with two RNA probes that include either the light or the heavy chain sequences of proEP, respectively. The two antibodies reacted with enterocytes, accentuated on the brush border, and goblet cells, with increasing intensity from the bottom of crypts to the top of villi. Paneth cells, neuroendocrine cells, Brunner's glands, lymphocytes, smooth muscle, or connective tissue did not react with the antibodies. The two RNA probes detected EP mRNA expression only in enterocytes and goblet cells. EP is produced in enterocytes and goblet cells, and the localization on the brush border of the cells is reasonable for the physiological activation of digestive enzymes. Interestingly, the antibodies reacted with tumor cells in duodenal polyps and adenocarcinoma at the duodenum but not in Brunner's gland adenoma. EP seems to be a marker of differentiated enterocytes and goblet cells, which suggests the existence of a common progenitor of these cells. Furthermore, EP may be a useful marker of tumor cells originating from these cells.

Expression, purification, and characterization of human enteropeptidase catalytic subunit in Escherichia coli

Enteropeptidase (synonym:enterokinase, EC 3.4.21.9) is a heterodimeric serine protease of the intestinal brush border that activates trypsinogen by highly specific cleavage of the trypsinogen activation peptide following the sequence (Asp)(4)-Lys. The DNA sequence encoding the light chain (catalytic subunit) of human enteropeptidase (GenBank Accession No. U09860) was synthesized from 26 oligonucleotides by polymerase chain reaction and cloned into plasmid pET-32a downstream to the gene of fusion partner thioredoxin immediately after the DNA sequence encoding enteropeptidase recognition site. The fusion protein thioredoxin/human enteropeptidase light chain was expressed in Escherichia coli BL21(DE3) strain in both soluble and insoluble forms. The soluble recombinant fusion protein failed to undergo autocatalytic cleavage and activation; however, autocatalytic cleavage and activation of recombinant human enteropeptidase light chain (L-HEP) were achieved by solubilization and renaturation of the fusion protein from inclusion bodies and the active L-HEP was purified on agarose-linked soybean trypsin inhibitor. The purified L-HEP cleaved the synthetic peptide substrate Gly-Asp-Asp-Asp-Asp-Lys-beta-naphthylamide with kinetic parameters K(m)=0.16 mM and k(cat)=115 s(-1) and small ester Z-Lys-SBzl with K(m)=140 microM, k(cat)=133 s(-1). L-HEP associated with soybean trypsin inhibitor slowly and small ester Z-Lys-SBzl cleavage was inhibited with K(i)(*)=2.3 nM. L-HEP digested thioredoxin/human epidermal growth factor fusion protein five times faster than equal activity units of bovine recombinant light chain (EKMax, Invitrogen) at the same conditions.

Mouse matriptase-2: identification, characterization and comparative mRNA expression analysis with mouse hepsin in adult and embryonic tissues

We report the identification and characterization of mouse matriptase-2 (m-matriptase-2), an 811-amino-acid protein composed of an N-terminal cytoplasmic domain, a membrane-spanning domain, two CUB (complement protein subcomponents C1r/C1s, urchin embryonic growth factor and bone morphogenetic protein 1) domains, three LDLR (low-density-lipoprotein receptor class A) domains and a C-terminal serine-protease domain. All m-matriptase-2 protein domain boundaries corresponded with intron/exon junctions of the encoding gene, which spans approx. 29 kb and comprises 18 exons. Matriptase-2 is highly conserved in human, mouse and rat, with the rat matriptase-2 gene ( r-maltriptase-2 ) predicted to encode transmembrane and soluble isoforms. Western-blot analysis indicated that m-matriptase-2 migrates close to its theoretical molecular mass of 91 kDa, and immunofluorescence analysis was consistent with the proposed surface membrane localization of this protein. Reverse-transcription PCR and in-situ -hybridization analysis indicated that m-matriptase-2 expression overlaps with the distribution of mouse hepsin (m-hepsin, a cell-surface serine protease identified in hepatoma cells) in adult tissues and during embryonic development. In adult tissues both are expressed at highest levels in liver, kidney and uterus. During embryogenesis m-matriptase-2 expression peaked between days 12.5 and 15.5. m-hepsin expression was biphasic, with peaks at day 7.5 to 8.5 and again between days 12.5 and 15.5. In situ hybridization of embryonic tissues indicated abundant expression of both m-matriptase-2 and m-hepsin in the developing liver and at lower levels in developing pharyngo-tympanic tubes. While m-hepsin was detected in the residual embryonic yolk sac and with lower intensity in lung, heart, gastrointestinal tract, developing kidney tubules and epithelium of the oral cavity, m-matriptase-2 was absent in these tissues, but strongly expressed within the nasal cavity by olfactory epithelial cells. Mechanistic insight into the potential role of this new transmembrane serine protease is provided by its novel expression profile in embryonic and adult mouse.

Cloning and Characterization of a Transmembrane-Type Serine Protease from Rat Kidney, a New Sodium Channel Activator

We have cloned the gene of a new transmembrane-type serine protease from rat kidney, which activates sodium channels. The amino acid sequence deduced from a full-length cDNA revealed that transmembrane serine protease-1 (TMSP-1) is a member of the clan SA/family S1 of serine proteases, comprising a 30 amino acid prepropeptide, a mature form sequence of 274 amino acids starting with the Ile-Val-Gly-Gly-Gln motif, and a common catalytic triad of serine proteases. The hydrophobic amino acid sequence in the carboxy-terminus of this enzyme suggests that it is a glycosylphosphatidylinositol-anchored protein. As revealed by quantitative reverse transcription-polymerase chain reaction analysis, it is highly expressed in kidney, small intestine, and stomach, and moderately expressed in lung, thymus, spleen and skin. The recombinant protease had an optimal pH at 9.0, selectively cleaved synthetic peptide substrates of trypsin, and was inhibited by aprotinin, leupeptin and benzamidine. Immunohistochemical studies revealed that this protease is predominantly expressed in cells from collecting ducts of the renal medulla. We also demonstrate that a C-terminally truncated variant of TMSP-1 significantly activates the epithelial sodium channel, and that its mRNA levels are upregulated by aldosterone. These observations suggest that it is a new member of the trypsin-type transmembrane proteases, which regulate sodium balance by activating the epithelial sodium channel.

Matriptase-2, a membrane-bound mosaic serine proteinase predominantly expressed in human liver and showing degrading activity against extracellular matrix proteins

We have identified and cloned a fetal liver cDNA encoding a new serine proteinase that has been called matriptase-2. This protein exhibits a domain organization similar to other members of an emerging family of membrane-bound serine proteinases known as type II transmembrane serine proteinases. Matriptase-2 contains a short cytoplasmic domain, a type II transmembrane sequence, a central region with several modular structural domains including two CUB (complement factor C1s/C1r, urchin embryonic growth factor, bone morphogenetic protein) domains and three low density lipoprotein receptor tandem repeats, and finally, a C-terminal catalytic domain with all typical features of serine proteinases. The human matriptase-2 gene maps to 22q12-q13, a location that differs from all type II transmembrane serine proteinase genes mapped to date. Immunofluorescence and Western blot analysis of COS-7 cells transfected with the isolated cDNA confirmed that matriptase-2 is anchored to the cell surface. Matriptase-2 was expressed in Escherichia coli, and the purified recombinant protein hydrolyzed synthetic substrates used for assaying serine proteinases and endogenous proteins such as type I collagen, fibronectin, and fibrinogen. Matriptase-2 could also activate single-chain urokinase plasminogen activator, albeit with low efficiency. These activities were abolished by inhibitors of serine proteinases but not by inhibitors of other classes of proteolytic enzymes. Northern blot analysis demonstrated that matriptase-2 transcripts are only detected at significant levels in both fetal and adult liver, suggesting that this novel serine proteinase may play a specialized role in matrix remodeling processes taking place in this tissue during development or in adult tissues.

A novel gene encoding a putative transmembrane protein with two extracellular CUB domains and a low-density lipoprotein class A module: isolation of alternatively spliced isoforms in retina and brain

We report herein the cDNA cloning of a novel retina and brain specific gene from mouse and human encoding a putative transmembrane protein with an N-terminal signal sequence and two conserved extracellular CUB domains followed by a single copy of the low-density lipoprotein class A (LDLa) module. The mouse and human genes, termed NETO1 (neuropilin and tolloid like-1), display sequence identities of 87% at the nucleotide and 95% at the protein level. The human NETO1 gene comprises 13 exons on chromosome 18q22-q23 and gives rise to three different mRNA isoforms. Two alternative leader exons 1a and 1b generate transcripts that translate into putative signal peptides with individual sequence composition but otherwise do not affect the primary structure of the mature NETO1 protein. Usage of the internal exon 5 is restricted to the retinal tissue and generates a truncated transcript that codes for a putative soluble protein, termed sNETO1, with only one copy of the CUB domain while lacking the LDLa module. NETO1 exhibits 57% identity to the deduced amino acid sequence of a non-annotated nucleotide sequence in the GenBank database, therefore designated NETO2. Both NETO1 and NETO2 share an identical and unique domain structure thus representing a novel subfamily of CUB- and LDLa-containing proteins. The cytoplasmic domains of NETO1 and NETO2 are not homologous to other known protein sequences but contain a conserved FXNPXY-like motif, which is essential for the internalization of clathrin coated pits during endocytosis or alternatively, may be implicated in intracellular signaling pathways.

Spinesin/TMPRSS5, a novel transmembrane serine protease, cloned from human spinal cord

A cDNA encoding a novel serine protease, which we designated spinesin, has been cloned from human spinal cord. The longest open reading frame was 457 amino acids. A homology search revealed that the human spinesin gene was located at chromosome 11q23 and contained 13 exons, the gene structure being similar to that of TMPRSS3 whose gene is also located on 11q23. Spinesin has a simple type II transmembrane structure, consisting of, from the N terminus, a short cytoplasmic domain, a transmembrane domain, a stem region containing a scavenger receptor-like domain, and a serine protease domain. Unlike TMPRSS3, it carries no low density lipoprotein receptor domain in the stem region. The extracellular region carries five N-glycosylation sites. The sequence of the protease domain carried the essential triad His, Asp, and Ser and showed some similarity to that of TMPRSS2, hepsin, HAT, MT-SP1, TMPRSS3, and corin, sharing 45.5, 41.9, 41.3, 40.3, 39.1, and 38.5% identity, respectively. The putative mature protease domain preceded by H(6)DDDDK was produced in Escherichia coli, purified, and successfully activated by immobilized enterokinase. Its optimal pH was about 10. It cleaved synthetic substrates for trypsin, which is inhibited by p-amidinophenylmethanesulfonyl fluoride hydrochloride but not by antipain or leupeptin. Northern blot analysis against mRNA from human tissues including liver, lung, placenta, and heart demonstrated a specific expression of spinesin mRNA in the brain. Immunohistochemically, spinesin was predominantly expressed in neurons, in their axons, and at the synapses of motoneurons in the spinal cord. In addition, some oligodendrocytes were clearly stained. These results indicate that spinesin is transported to the synapses through the axons after its synthesis in the cytoplasm and may play important roles at the synapses. Further analyses are required to clarify its roles at the synapses and in oligodendrocytes.

Catalytic domain structures of MT-SP1/matriptase, a matrix-degrading transmembrane serine proteinase

The type II transmembrane multidomain serine proteinase MT-SP1/matriptase is highly expressed in many human cancer-derived cell lines and has been implicated in extracellular matrix re-modeling, tumor growth, and metastasis. We have expressed the catalytic domain of MT-SP1 and solved the crystal structures of complexes with benzamidine at 1.3 A and bovine pancreatic trypsin inhibitor at 2.9 A. MT-SP1 exhibits a trypsin-like serine proteinase fold, featuring a unique nine-residue 60-insertion loop that influences interactions with protein substrates. The structure discloses a trypsin-like S1 pocket, a small hydrophobic S2 subsite, and an open negatively charged S4 cavity that favors the binding of basic P3/P4 residues. A complementary charge pattern on the surface opposite the active site cleft suggests a distinct docking of the preceding low density lipoprotein receptor class A domain. The benzamidine crystals possess a freely accessible active site and are hence well suited for soaking small molecules, facilitating the improvement of inhibitors. The crystal structure of the MT-SP1 complex with bovine pancreatic trypsin inhibitor serves as a model for hepatocyte growth factor activator inhibitor 1, the physiological inhibitor of MT-SP1, and suggests determinants for the substrate specificity.

Mutations in the proenteropeptidase gene are the molecular cause of congenital enteropeptidase deficiency

Enteropeptidase (enterokinase [E.C.3.4.21.9]) is a serine protease of the intestinal brush border in the proximal small intestine. It activates the pancreatic proenzyme trypsinogen, which, in turn, releases active digestive enzymes from their inactive pancreatic precursors. Congenital enteropeptidase deficiency is a rare recessively inherited disorder leading, in affected infants, to severe failure to thrive. The genomic structure of the proenteropeptidase gene (25 exons, total gene size 88 kb) was characterized in order to perform DNA sequencing in three clinically and biochemically proved patients with congenital enteropeptidase deficiency who were from two families. We found compound heterozygosity for nonsense mutations (S712X/R857X) in two affected siblings and found compound heterozygosity for a nonsense mutation (Q261X) and a frameshift mutation (FsQ902) in the third patient. In accordance with the biochemical findings, all four defective alleles identified are predicted null alleles leading to a gene product not containing the active site of the enzyme. These data provide first evidence that proenteropeptidase-gene mutations are the primary cause of congenital enteropeptidase deficiency.

Cloning and characterization of the cDNA and gene for human epitheliasin

Previously, we reported cloning and characterization of the mouse gene, epitheliasin. In the present work we cloned the cDNA of the full-length human orthologue and characterized its gene including 2 kb of 5' flanking sequence. Analysis of epitheliasin gene expression in adult tissues shows that it is expressed as 3.4 kb and 2 kb transcripts. The major 3.4 kb transcript is observed in the following order: prostate > colon > small intestine > pancreas > kidney > lung > liver. Epitheliasin transcripts in fetal tissues are observed only in kidney and lung. In situ hybridization analysis of tissues revealed that epitheliasin was preferentially expressed in epithelial cells. The gene consists of 14 exons and 13 introns based on comparison with its cDNA sequence. In the 5' flanking region, we identified two transcription start sites and three CpG islands encompassing a number of potential regulatory elements including SP1, SREBP, GRE/PRE and ERE. The region upstream of the transcription sites lacks a TATA box but contains an initiator-like element as well as a downstream promoter-like element. In vitro experiments with lymph node carcinoma of prostate (LNCaP) cells revealed that the epitheliasin gene was induced by androgens and the induction was not blocked by cycloheximide indicating that the induction required no intermediate protein factors. Immunoprecipitation analysis showed that androgens strongly increased epitheliasin protein levels.

Localization of the mosaic transmembrane serine protease corin to heart myocytes

Corin cDNA encodes an unusual mosaic type II transmembrane serine protease, which possesses, in addition to a trypsin-like serine protease domain, two frizzled domains, eight low-density lipoprotein (LDL) receptor domains, a scavenger receptor domain, as well as an intracellular cytoplasmic domain. In in vitro experiments, recombinant human corin has recently been shown to activate pro-atrial natriuretic peptide (ANP), a cardiac hormone essential for the regulation of blood pressure. Here we report the first characterization of corin protein expression in heart tissue. We generated antibodies to two different peptides derived from unique regions of the corin polypeptide, which detected immunoreactive corin protein of approximately 125-135 kDa in lysates from human heart tissues. Immunostaining of sections of human heart showed corin expression was specifically localized to the cross striations of cardiac myocytes, with a pattern of expression consistent with an integral membrane localization. Corin was not detected in sections of skeletal or smooth muscle. Corin has been suggested to be a candidate gene for the rare congenital heart disease, total anomalous pulmonary venous return (TAPVR) as the corin gene colocalizes to the TAPVR locus on human chromosome 4. However examination of corin protein expression in TAPVR heart tissue did not show evidence of abnormal corin expression. The demonstrated corin protein expression by heart myocytes supports its proposed role as the pro-ANP convertase, and thus a potentially critical mediator of major cardiovascular diseases including hypertension and congestive heart failure.

Human genetic diseases of proteolysis

Although in the past protein stability commonly has been considered an inherent property of a given protein, the truth is far more complex. Elaborate enzymatic systems exist in multiple intracellular compartments to hydrolyze proteins. These systems are capable of providing a sensitive mechanism to regulate protein expression, a mechanism that is complementary to the transcriptional and translational control mechanisms that influence protein synthesis. The power of regulated proteolysis has been well-demonstrated in the abrupt degradation of cyclins that underlies eukaryotic cell cycle progression. Coincidental with the recent rapid gains in understanding proteolysis at a biochemical level, several human diseases have been found to result from disordered proteolysis. This article reviews several examples of human disease resulting from mutations of genes encoding serine proteases, cysteine proteases, and their inhibitors. Examples are also presented of human diseases resulting from disorders in the highly intricate ubiquitin-proteasome pathway of protein degradation. It is certain that many more human diseases will be associated in the future with disorders of proteolysis.

Activation of recombinant proenteropeptidase by duodenase

Duodenase, a serine proteinase from bovine Brunner's (duodenal) glands that was predicted to be a natural activator of enteropeptidase zymogen, cleaves and activates recombinant single-chain bovine proenteropeptidase (kcat/Km = 2700 M(-1) s(-1)). The measured rate of proenteropeptidase cleavage by duodenase was about 70-fold lower compared with the rate of trypsin-mediated cleavage of the zymogen. The role of duodenase is supposed to be the primary activator of proenteropeptidase maintaining a certain level of active enteropeptidase in the duodenum. A new scheme of proteolytic activation cascade of digestive proteases is discussed.

Reverse biochemistry: use of macromolecular protease inhibitors to dissect complex biological processes and identify a membrane-type serine protease in epithelial cancer and normal tissue

Serine proteases of the chymotrypsin fold are of great interest because they provide detailed understanding of their enzymatic properties and their proposed role in a number of physiological and pathological processes. We have been developing the macromolecular inhibitor ecotin to be a "fold-specific" inhibitor that is selective for members of the chymotrypsin-fold class of proteases. Inhibition of protease activity through the use of wild-type and engineered ecotins results in inhibition of rat prostate differentiation and retardation of the growth of human PC-3 prostatic cancer tumors. In an effort to identify the proteases that may be involved in these processes, reverse transcription-PCR with PC-3 poly(A)+ mRNA was performed by using degenerate oligonucleotide primers. These primers were designed by using conserved protein sequences unique to chymotrypsin-fold serine proteases. Five proteases were identified: urokinase-type plasminogen activator, factor XII, protein C, trypsinogen IV, and a protease that we refer to as membrane-type serine protease 1 (MT-SP1). The cloning and characterization of the MT-SP1 cDNA shows that it encodes a mosaic protein that contains a transmembrane signal anchor, two CUB domains, four LDLR repeats, and a serine protease domain. Northern blotting shows broad expression of MT-SP1 in a variety of epithelial tissues with high levels of expression in the human gastrointestinal tract and the prostate. A His-tagged fusion of the MT-SP1 protease domain was expressed in Escherichia coli, purified, and autoactivated. Ecotin and variant ecotins are subnanomolar inhibitors of the MT-SP1 activated protease domain, suggesting a possible role for MT-SP1 in prostate differentiation and the growth of prostatic carcinomas.

Genomic organization and chromosomal localization of the human CD163 (M130) gene: a member of the scavenger receptor cysteine-rich superfamily

The human protein CD163 (M130) is a member of the scavenger receptor cysteine-rich (SRCR) superfamily, which is exclusively expressed by monocytes and macrophages. Here, we investigated the genomic organization and the chromosomal localization of the human CD163 gene. The CD163 gene is composed of 17 exons and 16 introns and spans over 35 kb. Each of its nine SRCR domains is encoded by a separate exon, which is similar to other members of the group B SRCR subfamily. Two cytoplasmic variants of CD163 arise from alternative splicing of intron 15, while a truncated and an extracellular variant results from alternative splicing of intron 5 or intron 7, respectively. Using fluorescence in situ hybridization we mapped this gene to the human chromosome 12p13. The transcription initiation sites of the CD163 gene were determined and the 5'-flanking region was sequenced. The nucleotide analysis revealed several putative binding sites for transcription factors, which have been shown to play an important role in myeloid specific gene expression. In addition, we identified a L1 element located 1.4 kb upstream of the major transcription initiation site.

Apical sorting of bovine enteropeptidase does not involve detergent-resistant association with sphingolipid-cholesterol rafts

Enteropeptidase is a heterodimeric type II membrane protein of the brush border of duodenal enterocytes. In this location, enteropeptidase cleaves and activates trypsinogen, thereby initiating the activation of other intestinal digestive enzymes. Recombinant bovine enteropeptidase was sorted directly to the apical surface of polarized Madin-Darby canine kidney cells. Replacement of the cytoplasmic and signal anchor domains with a cleavable signal peptide (mutant proenteropeptidase lacking the amino-terminal signal anchor domain (dSA-BEK)) caused apical secretion. The additional amino-terminal deletion of a mucin-like domain (HL-BEK) resulted in secretion both apically and basolaterally. Further deletion of the noncatalytic heavy chain (L-BEK) resulted in apical secretion. Thus enteropeptidase appears to have at least three distinct sorting signals as follows: the light chain (L-BEK) directs apical sorting, addition of most of the heavy chain (HL-BEK) inhibits apical sorting, and addition of the mucin-like domain (dSA-BEK) restores apical sorting. Inhibition of N-linked glycosylation with tunicamycin or disruption of microtubules with colchicine caused L-BEK to be secreted equally into apical and basolateral compartments, whereas brefeldin A caused basolateral secretion of L-BEK. Full-length BEK was not found in detergent-resistant raft domains of Madin-Darby canine kidney cells or baby hamster kidney cells. These results suggest apical sorting of enteropeptidase depends on N-linked glycosylation of the serine protease domain and an amino-terminal segment that includes an O-glycosylated mucin-like domain and three potential N-glycosylation sites. In contrast to many apically targeted proteins, enteropeptidase does not form detergent-resistant associations with sphingolipid-cholesterol rafts.

Cloning and characterization of the cDNA for human airway trypsin-like protease

Previously we isolated a trypsin-like enzyme designated human airway trypsin-like protease from the sputum of patients with chronic airway diseases. This paper describes the cDNA cloning, characterization of the primary protein structure deduced from the cDNA, and gene expression of this enzyme in various human tissues. We obtained an entire 1517-base pair sequence of cDNA with an open reading frame encoding a polypeptide with 418-amino acid residues. The polypeptide consisted of a 232-residue catalytic region and a 186-residue noncatalytic region with a hydrophobic putative transmembrane domain near the NH2 terminus. The polypeptide was suggested to be a type II integral membrane protein in which the COOH-terminal catalytic region is extracellular. Therefore, this protein is thought to be synthesized as a membrane-bound precursor and to mature to a soluble and active protease by limited proteolysis. It showed 29-38% identity in the sequence of the catalytic region with human hepsin, enteropeptidase, acrosin, and mast cell tryptase. The noncatalytic region had little similarity to other known proteins. In Northern blot analysis a transcript of 1.9 kilobases was detectable most prominently in the trachea among 17 human tissues examined.

Structure of murine enterokinase (enteropeptidase) and expression in small intestine during development

Enterokinase (enteropeptidase) is expressed only in proximal small intestine, where it initiates digestive enzyme activation by converting trypsinogen into trypsin. To investigate this restricted expression pattern, mouse enterokinase cDNA was cloned, and the distribution of enterokinase mRNA and enzymatic activity were determined in adult mice and during gestation. Analysis of enterokinase sequences showed that a mucinlike domain near the NH2 terminus is composed of repeated approximately 15-amino acid Ser/Thr-rich motifs. By Northern blotting and trypsinogen activation assays, enterokinase mRNA and enzymatic activity were undetectable in stomach, abundant in duodenum, and decreased distally until they were undetectable in midjejunum, ileum, and colon. By in situ mRNA hybridization, enterokinase mRNA was localized to the enterocytes throughout the villus. Expression was not observed in goblet cells, Paneth cells, or Brunner's glands. Enterokinase mRNA and enzymatic activity were not detected in the duodenum of fetal mice but were easily detected in the duodenum on postnatal days 2-6. Both enterokinase mRNA and enzymatic activity decreased to very low levels after day 7 but increased after weaning and reached a high level characteristic of adult life by day 60. Therefore, in mice, duodenal enterocytes are the major type of cells expressing enterokinase, which appears to be regulated at the level of mRNA abundance.

Subcellular localization, substrate specificity and crystallization of duodenase, a potential activator of enteropeptidase

Duodenase, a serine protease from bovine duodenum mucosa, was located in endoplasmic reticulum, the Golgi secretory granules of epithelial cells and ducts of Brunner's glands by the A-gold immunocytochemical method. Duodenase exhibits trypsin-like and chymotrypsin-like specificities with a preference for substrates having lysine at the P1 and proline at the P2 positions. The kinetic constants for the hydrolysis of 21 potential duodenase substrates are reported. The best substrates were found to be alpha-N-tosylglycylprolyllysine 4-nitroanilide (k[cat]/Km of 35000 M[-1] s[-1]), alpha-N-succinylthreonylprolyllysine 4-nitroanilide (k[cat]/Km of 18000 M[-1] s[-1]) and alpha-N-serylprolyllysine 4-nitroanilide (k[cat]/Km of 2600 m[-1] s[-1]), all of which contain the P1-P3 sequence of the enteropeptidase zymogen/activation site. On the basis of its catalytic properties and sites of localization, duodenase has been postulated to be an activator of the enteropeptidase precursor. A tetradecapeptide (LVTQEVSPKIVGGS) having the P9-P5'sequence of the cleavage site of zymogen activation of bovine proenteropeptidase was synthesized, and kinetic parameters of its hydrolysis by duodenase were determined (Km of 87 microM; k[cat] of 1.4 s[-1]; k[cat]/Km of 16000 M[-1] s[-1]). Crystals of duodenase frozen in a stream of liquid nitrogen diffracted synchrotron X-rays to 0.2-nm resolution.

Gene identification and DNA sequence analysis in the GC-poor 20 megabase region of human chromosome 21

In contrast to the distal half of the long arm of chromosome 21, the proximal half of approximately 20 megabases of DNA, including 21q11-21 bands, is low in GC content, CpG islands, and identified genes. Despite intensive searches, very few genes and cDNAs have been found in this region. Since the 21q11-21 region is associated with certain Down syndrome pathologies like mental retardation, the identification of relevant genes in this region is important. We used a different approach by constructing microdissection libraries specifically for this region and isolating unique sequence microclones for detailed molecular analysis. We found that this region is enriched with middle and low-copy repetitive sequences, and is also heavily methylated. By sequencing and homology analysis, we identified a significant number of genes/cDNAs, most of which appear to belong to gene families. In addition, we used unique sequence microclones in direct screening of cDNA libraries and isolated 12 cDNAs for this region. Thus, although the 21q11-21 region is gene poor, it is not completely devoid of genes/cDNAs. The presence of high proportions of middle and low-copy repetitive sequences in this region may have evolutionary significance in the genome organization and function of this region. Since 21q11-21 is heavily methylated, the expression of genes in this region may be regulated by a delicate balance of methylation and demethylation, and the presence of an additional copy of chromosome 21 may seriously disturb this balance and cause specific Down syndrome anomalies including mental retardation.

Distribution of myristoyl-CoA:protein N-myristoyl transferase activity in rabbit intestine

Myristoyl-CoA:protein N-myristoyl transferase (NMT) attaches the fatty acid, myristate, to the amino-terminal glycine residue of various proteins involved in cellular regulation and/or signal transduction. We report differences in the activity and properties of NMT in New Zealand rabbit small intestine, ascending colon and descending colon. The mucosa of the small intestine, ascending colon and descending colon was assayed for NMT activity using peptides of known myristoylated proteins (pp60src and catalytic subunit of cAMP dependent protein kinase). Total NMT activity per gram tissue was 5-fold higher in the small intestine and 1.5-fold higher in the ascending colon than in the descending colon. Smooth muscle from the colon also contained low levels of NMT activity. NMT activity was 2- to 3-fold higher in the particulate fraction than in the cytosolic fraction of the mucosa in the descending colon. The apparent molecular mass of NMT in the intestine mucosa was 78 kDa.