Inhibition of kallikrein-related peptidases by the serine protease inhibitor of Kazal-type 6

Kallikrein-related peptidases (KLKs) are a group of serine proteases, expressed in several tissues. Their activity is regulated by inhibitors including members of the serine protease of Kazal-type (SPINK) family. Recently, we discovered that SPINK6 is expressed in human skin and inhibits KLK5, KLK7, KLK14 but not KLK8. In this study we tested whether SPINK6 inhibits other members of the KLK family and caspase-14. Using chromogenic substrates, SPINK6 exhibited inhibitory activity against KLK12 and KLK13 with K_i around 1 nM, KLK4 with K_i = 27.3 nM, KLK6 with K_i = 140 nM, caspase-14 with a K_i approximating 1 μM and no activity against KLK1, KLK3 and KLK11. Taken together, SPINK6 is a potent inhibitor of distinct KLKs members.     

Inhibition profiles of human tissue kallikreins by serine protease inhibitors

Accumulated evidence has shown that human tissue kallikreins (hKs), a group of 15 homologous secreted serine proteases, are novel cancer biomarkers. We report here the inhibition profiles of selected hKs, including hK5, hK7, hK8, hK11, hK12, hK13, and hK14, by several common serine protease inhibitors (serpins) found in plasma. The association constants for the binding of serpins to kallikreins were determined and compared. Protein C inhibitor was found to be the fastest-binding serpin for most of these hKs. alpha2-Antiplasmin, alpha1-antichymotrypsin, and alpha1-antitrypsin also showed rapid inhibition of certain hKs. Kallistatin exhibited fast inhibition only with hK7. Our data demonstrate that these hKs are specifically regulated by certain serpins and their distinct inhibition profiles will be valuable aids in various aspects of kallikrein research.     

柞蚕Kazal型丝氨酸蛋白酶抑制剂ApKTSPI基因克隆及表达特征分析

【目的】克隆柞蚕(Antheraea pernyi)Kazal型丝氨酸蛋白酶抑制剂(ApKTSPI)基因的cDNA序列并进行序列分析,研究ApKTSPI基因的组织表达分布及病原物免疫刺激后的表达模式,原核表达ApKTSPI。【方法】利用RACE-PCR方法扩增柞蚕ApKTSPI基因全长cDNA,生物信息学软件进行序列分析,利用实时定量PCR检测柞蚕ApKTSPI基因的组织分布及免疫刺激后的表达模式,利用pET-28a载体在大肠杆菌BL21中融合表达ApKTSPI。【结果】柞蚕ApKTSPI基因的cDNA全长568 bp,开放阅读框编码96个氨基酸,含一个Kazal结构域。ApKTSPI基因在柞蚕5龄幼虫脂肪体中特异性高表达,在核型多角体病毒、大肠杆菌和白僵菌免疫刺激后表达量都能上调,但上调的程度和时间都不同。ApKTSPI在大肠杆菌中成功诱导表达。【结论】获得了柞蚕ApKTSPI基因的cDNA全长,并研究了ApKTSPI基因的表达模式,为进一步研究其在柞蚕免疫中的功能及作用机理奠定了基础。     

叉角厉蝽丝氨酸蛋白酶及抑制剂基因的克隆与表达分析

为明确叉角厉蝽Eocanthecona furcellata (Wolff)丝氨酸蛋白酶基因EfSP1及抑制剂基因EfSPI20的基因序列特征和时空转录特征,为其生理功能研究奠定基础。利用PCR克隆技术获得叉角厉蝽唾液腺EfSPI20和EfSP1的完整开放阅读框(Open reading frame, ORF)序列,使用生物信息学软件进行序列分析以及系统进化分析,采用实时荧光定量PCR (Real time quantitativate PCR,RT-qPCR)分析两个基因分别在叉角厉蝽不同发育时期和组织中的表达特征。结果表明,EfSPI20与EfSP1基因完整开放阅读框长度分别为378 bp和921 bp,分别编码125个氨基酸和306个氨基酸,预测均为亲水蛋白质,理论分子量分别为13.48 kDa和33.82 kDa,等电点分别为6.68和5.80,分别有30个和23个氨基酸残基的信号肽序列,EfSPI20有跨膜结构域,EfSP1无跨膜结构域。序列比对显示叉角厉蝽EfSPI20与茶翅蝽Halyomorpha halys PPI同源性最高,氨基酸序列一致性达58%;EfSP1与稻绿蝽Nezara viridula SP同源性最高,氨基酸序列一致性达66%;系统发育树显示叉角厉蝽与同为蝽科的茶翅蝽和稻绿蝽物种亲缘关系近。EfSPI20基因在雌雄成虫和唾液腺中高表达,推测EfSPI20可能具有抑制胰蛋白酶活性的功能和与叉角厉蝽的捕食消化相关;EfSP1基因在卵期、卵巢和肠道中高表达,推测EfSP1可能与叉角厉蝽的生殖功能和蛋白消化相关。     

Expression, purification and characterization of recombinant human serine proteinase inhibitor Kazal-type 6 (SPINK6) in Pichia pastoris

Human serine proteinase inhibitor Kazal-type 6 (SPINK6) belongs to the medically important SPINK family. Malfunctions of SPINK members are linked to many diseases, including pancreatitis, skin barrier defects, and cancer. SPINK6 has been shown to selectively inhibit Kallikrein-related peptidases (KLKs) in human skin. As a SPINK protein, it contains a typical Kazal domain, which requires three intramolecular disulfide bonds for correct folding and activity. Preparation of functional protein is a prerequisite for studying this important human factor. Here, we report the successful generation of tagless SPINK6 using a yeast expression system. The recombinant protein was secreted and purified by cation exchange and size-exclusion chromatography. The protein identity was confirmed by MALDI-TOF MS and N-terminal sequencing. Pichia pastoris-derived recombinant human SPINK6 (rhSPINK6) showed higher inhibitory activity against Kallikrein-related peptidase 14 (KLK14) (K(i)=0.16 nM) than previously reported Escherichia coli-derived rhSPINK6 (K(i)=0.5 nM). This protein also exhibited moderate inhibition of bovine trypsin (K(i)=33 nM), while previous E. coli-derived rhSPINK6 did not. The results indicate that P. pastoris is a better system to generate active rhSPINK6, warranting further studies on this medically important SPINK family candidate.     

大豆蚜Kazal型丝氨酸蛋白酶抑制剂基因AgKaSPI对蜡蚧刺束梗孢菌侵染的表达响应

[目的]探究Kazal型丝氨酸蛋白酶抑制剂KaSPI在大豆蚜Aphis glycines的生长发育、消化和免疫防御等过程中的作用.[方法]基于大豆蚜转录组数据PCR克隆大豆蚜Kazal型丝氨酸蛋白酶抑制剂基因cDNA序列;qRT-PCR分别检测AgKaSPI在大豆蚜1-4龄若虫和成虫以及蜡蚧刺束梗孢菌Akanthomy...     

Accurate disulfide formation in Escherichia coli: overexpression and characterization of the first domain (HF6478) of the multiple Kazal-type inhibitor LEKTI

The human hemofiltrate peptide HF6478, a putative serine proteinase inhibitor, which is part of the precursor protein LEKTI, was cloned, overexpressed, and purified. HF6478 contains two disulfide bridges with 1-4, 2-3 connectivity, sharing partial homology to Kazal-type domains and other serine proteinase inhibitors. It was expressed as thioredoxin (Trx) fusion protein, and disulfide formation occurred in the oxidative cytoplasm of Escherichia coli Origami (DE3) strain which carries a trxB(-)/gor522(-) double mutation. The soluble fusion protein was purified using metal-chelating affinity chromatography. Cleavage of the Trx fusion protein with factor Xa and subsequent purification yielded the final product in amounts sufficient for structural studies. Characterization of recombinant HF6478 was done by amino acid sequencing, mass spectrometry, capillary zone electrophoresis, and CD spectroscopy. Taking the blood filtrate peptide HF6478 as example, we present a strategy which should facilitate the expression of different extracellular proteins in the E. coli cytoplasm.     

Primary structure of human alpha 2-antiplasmin, a serine protease inhibitor (serpin)

The plasma protein alpha 2-antiplasmin is the main physiological inhibitor of the serine protease plasmin, which is responsible for the dissolution of fibrin clots. We have determined the primary structure of mature human alpha 2-antiplasmin by DNA sequencing of overlapping cDNA fragments prepared from human liver mRNA. cDNA clones were identified by hybridization with a 48-base pair deoxyoligonucleotide probe deduced from the sequence of a 16-amino acid peptide of alpha 2-antiplasmin. Mature human alpha 2-antiplasmin contains 452 amino acids. It is homologous (23-28%) with five other proteins belonging to the serine protease inhibitor (serpin) superfamily. Its reactive site, i.e. the peptide bond cleaved by reaction with its primary target enzyme, plasmin, consists of Arg364-Met365. This dipeptide corresponds to the reactive site Met358-Ser359 of the archetypal serpin, alpha 1-antitrypsin.     

Suppression of human leukocyte tumor necrosis factor secretion by the serine protease inhibitor p-toluenesulfonyl-L-arginine methyl ester (TAME)

The addition of the serine protease inhibitor p-toluenesulfonyl-L-arginine methyl ester (TAME) to human peripheral blood mononuclear cells suppressed TNF secretion in a concentration dependent manner. At a concentration 10 mM TAME leukocyte TNF release was completely inhibited without decreasing the secretion of IL-1 alpha. Simultaneously exposing leukocytes to 10 mM TAME and either 1000 U/ml IFN-gamma or 10 micrograms/ml LPS reduced the quantity of TNF secreted by 75% and 47%, respectively, when compared with the effect of either IFN-gamma or LPS alone. TAME was most effective when added to leukocytes at the initiation of culture and the suppressive effects of this protease inhibitor were reversible by washing the cells. TAME suppressed TNF secretion without affecting either the level of TNF mRNA or the expression of cell surface cytokine. These findings suggest that leukocyte TNF secretion is dependent upon the action of one or more serine proteases.     

Biochemical features,molecular biology and clinical relevance of the human 15-domain serine proteinase inhibitor LEKTI

Based on the isolation of a 55 amino acid peptide from human hemofiltrate, we cloned the cDNA for a novel human 15-domain serine proteinase inhibitor termed LEKTI. A trypsin-inhibiting activity was demonstrated for three different domains. High levels of expression of the corresponding gene were detected in oral mucosa, followed by the tonsils, parathyroid glands, thymus, and trachea. Hovnanian and coworkers recently found that certain mutations within the LEKTI gene are linked to the severe congenital disease Netherton syndrome and atopic manifestations (including asthma). Thus, a future therapeutic use of LEKTI is conceivable.     

Effect of the serine protease inhibitor N-tosyl-l-phenylalanine-chloromethyl ketone (TPCK) on MCF-7 mammary tumour cells growth and differentiation

Previous studies from this and other laboratories indicated that the oestrogen-regulated heat shock protein HSP27 is involved in the control of MCF-7 cells growth and differentiation, as it also appears to be in other cell types, including osteoblasts and HL-60 cells. In the latter instance, induction of differentiation is associated with the downregulation of myeloblastin, a serine protease now identified as proteinase 3 (hence its designation as PR3/Mbn), mirrored by an increase in the cellular content of the small heat shock protein HSP27, a substrate to this enzyme. Besides, antisense inhibition of PR3/Mbn production sufficed for inducing HL-60 cells monocytic differentiation. This prompted us to examine the hypothesis that a post-translational control on HSP27 levels (and by this on differentiation) by a serine protease might also be operating in human mammary tumour cells. As part of our attempt to evaluate this hypothesis, the present work consisted of testing the effects of a treatment of MCF-7 cells with the serine protease inhibitor N-tosyl-L-phenylalanine-chloromethyl ketone (TPCK). Our data show that this resulted in a four-fold increase in HSP27 content, associated with a 2.5-fold decrease in growth rate, the formation of cytoplasmic vesicles and increased secretion of 52 kDa peptides, identified by Western immunoblot as the isoforms of the oestrogen-regulated protein, cathepsin D. TPCK only affected growth in MDAMB-231 cells (in which HSP27 levels are very low and remained below MCF-7 cells basal levels after treatment) and failed to affect L929 cells, in which the hsp27 gene is silent. This provides circumstantial support for the assumption that effects of TPCK on the MCF-7 cells phenotype are linked to the associated increase in HSP27 content. Our recent demonstration that MCF-7 cells do in fact express PR3/Mbn fits with our concept and opens the way to test it directly, using antisense strategy.     

Structural basis for dual-inhibition mechanism of a non-classical Kazal-type serine protease inhibitor from horseshoe crab in complex with subtilisin

Serine proteases play a crucial role in host-pathogen interactions. In the innate immune system of invertebrates, multi-domain protease inhibitors are important for the regulation of host-pathogen interactions and antimicrobial activities. Serine protease inhibitors, 9.3-kDa CrSPI isoforms 1 and 2, have been identified from the hepatopancreas of the horseshoe crab, Carcinoscorpius rotundicauda. The CrSPIs were biochemically active, especially CrSPI-1, which potently inhibited subtilisin (Ki = 1.43 nM). CrSPI has been grouped with the non-classical Kazal-type inhibitors due to its unusual cysteine distribution. Here we report the crystal structure of CrSPI-1 in complex with subtilisin at 2.6 Å resolution and the results of biophysical interaction studies. The CrSPI-1 molecule has two domains arranged in an extended conformation. These two domains act as heads that independently interact with two separate subtilisin molecules, resulting in the inhibition of subtilisin activity at a ratio of 1:2 (inhibitor to protease). Each subtilisin molecule interacts with the reactive site loop from each domain of CrSPI-1 through a standard canonical binding mode and forms a single ternary complex. In addition, we propose the substrate preferences of each domain of CrSPI-1. Domain 2 is specific towards the bacterial protease subtilisin, while domain 1 is likely to interact with the host protease, Furin. Elucidation of the structure of the CrSPI-1: subtilisin (1∶2) ternary complex increases our understanding of host-pathogen interactions in the innate immune system at the molecular level and provides new strategies for immunomodulation.     

Homologous proteins with different folds: the three-dimensional structures of domains 1 and 6 of the multiple Kazal-type inhibitor LEKTI

We have determined the solution structures of recombinant domain 1 and native domain 6 of the multi-domain Kazal-type serine proteinase inhibitor LEKTI using multi-dimensional NMR spectroscopy. While two of the 15 potential inhibitory LEKTI domains contain three disulfide bonds typical of Kazal-type inhibitors, the remaining 13 domains have only two of these disulfide bridges. Therefore, they may represent a novel type of serine proteinase inhibitor. The first and the sixth LEKTI domain, which have been isolated from human blood ultrafiltrate, belong to this group. In spite of sharing the same disulfide pattern and a sequence identity of about 35% from the first to the fourth cysteine, the two proteins show different structures in this region. The three-dimensional structure of domain 6 consists of two helices and a beta-hairpin structure, and closely resembles the three-dimensional fold of classical Kazal-type serine proteinase inhibitors including the inhibitory binding loop. Domain 6 has been shown to be an efficient, but non-permanent serine proteinase inhibitor. The backbone geometry of its canonical loop is not as well defined as the remaining structural elements, providing a possible explanation for its non-permanent inhibitory activity. We conclude that domain 6 belongs to a subfamily of classical Kazal-type inhibitors, as the third disulfide bond and a third beta-strand are missing. The three-dimensional structure of domain 1 shows three helices and a beta-hairpin, but the central part of the structure differs remarkably from that of domain 6. The sequence adopting hairpin structure in domain 6 exhibits helical conformation in domain 1, and none of the residues within the putative P3 to P3' stretch features backbone angles that resemble those of the canonical loop of known proteinase inhibitors. No proteinase has been found to be inhibited by domain 1. We conclude that domain 1 adopts a new protein fold and is no canonical serine proteinase inhibitor.     

Interaction of Kazal-type inhibitor domains with serine proteinases: biochemical and structural studies

The interaction of domains of the Kazal-type inhibitor protein dipetalin with the serine proteinases thrombin and trypsin is studied. The functional studies of the recombinantly expressed domains (Dip-I+II, Dip-I and Dip-II) allow the dissection of the thrombin inhibitory properties and the identification of Dip-I as a key contributor to thrombin/dipetalin complex stability and its inhibitory potency. Furthermore, Dip-I, but not Dip-II, forms a complex with trypsin resulting in an inhibition of the trypsin activity directed towards protein substrates. The high resolution NMR structure of the Dip-I domain is determined using multi-dimensional heteronuclear NMR spectroscopy. Dip-I exhibits the canonical Kazal-type fold with a central alpha-helix and a short two-stranded antiparallel beta-sheet. Molecular regions essential for inhibitor complex formation with thrombin and trypsin are identified. A comparison with molecular complexes of other Kazal-type thrombin and trypsin inhibitors by molecular modeling shows that the N-terminal segment of Dip-I fulfills the structural prerequisites for inhibitory interactions with either proteinase and explains the capacity of this single Kazal-type domain to interact with different proteinases.     

Effects of the bumblebee (Bombus ignitus) venom serine protease inhibitor on serine protease and phospholipase A2 of B. ignitus venom

Bumblebee venom contains serine proteases and serine protease inhibitors. In this study, we characterized whether the bumblebee (Bombus ignitus) venom serine protease inhibitor (Bi-KTI) inhibits B. ignitus venom serine protease (Bi-VSP) or phospholipase A₂ (Bi-PLA₂). Bi-KTI did not inhibit Bi-VSP activity at pH 5.4 or 7.4, whereas Bi-KTI slightly inhibited Bi-VSP activity at pH 7.4 after a 30 min preincubation. The Bi-VSP activity that converts prothrombin into thrombin and fibrin into fibrin degradation products was not significantly affected by Bi-KTI. Additionally, Bi-KTI or Bi-VSP did not inhibit Bi-PLA₂ activity. These findings indicate that each bee venom component appears to a play a toxic role via a unique function.     

Inhibition of serine proteinases from human blood clotting system by squash inhibitor mutants

A series of six CMTI I variants mutated in the P(2)-P(4)' region of the canonical binding loop were used to probe the role of single amino acid substitutions on binding to the following human proteinases involved in blood clotting: plasmin, plasma kallikrein, factors X(a) and XII(a). The mutants were expressed as fusion proteins with the LE1413 hydrophobic polypeptide in Escherichia coli, purified from inclusion bodies, followed by cyanobromide cleavage and refolding. The mutants inhibited the proteinases with the association constants in the range 10(3)-10(9) M(-1). Inhibition of plasma kallikrein and factors X(a) and XII(a) could be improved up to 30-fold by single mutations. In contrast, neither of the introduced mutations increased inhibitory properties of CMTI I against plasmin. Additionally, using two inhibitors of natural origin, CMTI I (P(1) Arg) and CPTI II (P(1) Lys), we determined the effect of Lys-->Arg on binding to four proteinases. With the exception of plasmin (no effect), P(1) Arg resulted in up to 30-fold stronger binding than P(1) Lys.     

Inhibition of a novel sperm gelatinase in prawn sperm by the male reproduction-related Kazal-type peptidase inhibitor

Previously, we have identified and characterized a male reproduction-related kazal-type peptidase inhibitor (MRPINK) gene from the prawn, Macrobrachium rosenbergii. In the present study, MRPINK was discovered to have an inhibitory effect on the gelatinolytic activity of M. rosenbergii sperm and immunofluorescence analysis revealed it bound specifically onto the base of sperm. The proteolytic activity of sperm extracts to vitelline coat components was also detected to be interfered by MRPINK. Furthermore, a novel gelatinase on sperm was found to be specifically inhibited by MRPINK and was named M. rosenbergii sperm gelatinase (MSG). MSG was then isolated and purified by reversed-phase high performance liquid chromatography combining with gelatinolytic assay. By amino-terminal amino acid sequence analysis and molecular cloning, the primary structure of MSG was determined. The data presented in this study provided evidence that MRPINK has an inhibitory effect on the gelatinolytic activity as well as proteolytic activity of prawn sperm and specifically blocks the activity of MSG.