Cysteine proteinase from the eggs of the silkmoth, Bombyx mori: identification of a latent enzyme and characterization of activation and proteolytic processing in vivo and in vitro

A proteomics analysis of the ovarian development in females of Haemaphysalis longicornis

Haemaphysalis longicornis is an ixodid tick that can spread a wide variety of pathogens, affecting humans, livestock and wildlife health. The high reproductive capability of this species is initiated by the ingestion of a large amount of blood ingested by the engorged female tick. The degree of ovarian development is proportional to the number of eggs laid. Studying the regulatory mechanism of tick ovary development is relevant for the development of novel tick control methods. In this study, we used quantitative proteomics to study the dynamic changes in protein expression and protein phosphorylation during ovarian development of engorged female H. longicornis ticks. Synergistic action of many proteins (n = 3031) is required to achieve ovarian development and oocyte formation rapidly. Through bioinformatics analysis, changes in protein expressions and phosphorylation modifications in regulating the ovarian development of female ticks are described. Many proteins play an essential role during ovarian development. Also, protein phosphorylation appeared an important reproductive strategy to enable ticks to efficiently convert large amounts of blood in the ovaries into egg-producing components and ultimately produce many eggs.

Potential role of cytotoxic T-lymphocyte antigen 2 alpha in secretory activity of endocrine cells in mouse adenohypophysis

The peptide hormones of the adenohypophysis are produced by proteolytic processing of their prohormone precursors. Cathepsin L is known to function as a major proteolytic enzyme involved in the production of the peptide hormones. The structure of the propeptide region of cathepsin L is identical to cytotoxic T-lymphocyte antigen-2 alpha (CTLA-2α) which is also shown to exhibit selective inhibitory activities against cathepsin L. However, the specific cell types synthesizing CTLA-2α in mouse adenohypophysis and its functional implications as relevant in vivo have not been demonstrated. In this study, CTLA-2α expression in the adenohypophysis was evaluated by immunohistochemistry. In both male and female mice, strong immunoreactivity was specifically detected in folliculostellate (FS) cells surrounding endocrine cells which were delineated by CTLA-2α. These findings suggest that the CTLA-2α may be involved in the proteolytic processing and secretion of the hormones in the adenohypophysis through regulation of cathepsin L.

Purification and characterization of two cysteine proteinase inhibitors from silkworm, Bombyx mori

Cysteine proteinase inhibitors from silkworm are selective inhibitors with low molecular weight and regulate cathepsin L-like cysteine proteinase activity, thus, affecting silkworm metamorphosis. In a previous study, two cysteine proteinase inhibitors, BCPI and BmCPI, were identified in the silkworm genome. To characterize these inhibitors, we expressed and purified them in an Escherichia coli system and analyzed their structure and inhibitory activity in vitro. Both inhibitors showed strong tolerance to high temperature. Their CD spectra revealed that their secondary structures could be recovered by a gradual decrease in temperature. Compared to BCPI, BmCPI exhibited weak inhibitory activity toward cathepsin L. BCPI activity was significantly decreased when its C-terminus was truncated, whereas BmCPI activity increased considerably when the C-terminus tail of BCPI was attached to BmCPI. Additionally, the inhibitory activity of BCPI was strongly reduced if R31 was mutated to A31. In summary, two cysteine proteinase inhibitors from silkworm were characterized in the present study, which facilitates an understanding of the interaction mechanism between cysteine proteinase and its inhibitors in the silkworm.

Cathepsin L coexists with Cytotoxic T-lymphocyte Antigen-2 alpha in distinct regions of the mouse brain

Cathepsins B and L are two prominent members of cystein proteases with broad substrate specificity and are known to be involved in the process of intra- and extra-cellular protein degradation and turnover. The propeptide region of cathepsin L is identical to Cytotoxic T-lymphocyte antigen-2α (CTLA-2α) discovered in mouse activated T-cells and mast cells. CTLA-2α exhibits selective inhibitory activities against papain and cathepsin L. We previously demonstrated the distribution pattern of the CTLA-2α protein in mouse brain by immunohistochemistry, describing that it is preferentially localized within nerve fibre bundles than neuronal cell bodies. In the present study we report colocalization of cathepsin L and CTLA-2α by double labeling immunofluorescence analysis in the mouse brain. In the telencephalon, immunoreactivity was identified in cerebral cortex and subcortical structures, hippocampus and amygdala. Within the diencephalon intense colocalization was detected in stria medullaris of thalamus, mammillothalamic tract, medial habenular nucleus and choroid plexus. Colocalization signals in the mesencephalon were strong in the hypothalamus within supramammillary nucleus and lateroanterior hypothalamic nucleus while in the cerebellum was in the deep white matter, granule cell layer and Purkinje neurons but moderately in stellate, and basket cells of cerebellar cortex. The distribution pattern indicates that the fine equilibrium between synthesis and secretion of cathespin L and CTLA-2α is part of the brain processes to maintain normal growth and development. The functional implication of cathespin L coexistence with CTLA-2α in relation to learning, memory and disease mechanisms is discussed.

Two cathepsins B are responsible for the yolk protein hydrolysis in Culex quinquefasciatus

Despite the established role of Culex quinquefasciatus as a vector of various neurotropic viruses, such as the Rift Valley and West Nile viruses, as well as lymphatic filariasis, little is known regarding the organism’s reproductive physiology. As in other oviparous animals, vitellogenin, the most important source of nutrients for the embryo development, is digested by intracellular proteases. Using mass spectrometry, we have identified two cathepsin B homologues partially purified by self-proteolysis of Cx. quinquefasciatus total egg extract. The transcriptional profile of these two cathepsin B homologues was determined by quantitative RT-PCR, and the enzymatic activity associated with the peptidase was determined in ovaries after female engorgement. According to the VectorBase (vectorbase.org) annotation, both cathepsin B homologues shared approximately 66% identity in their amino acid sequences. The two cathepsin B genes are expressed simultaneously in the fat body of the vitellogenic females, and enzymatic activity was detected within the ovaries, suggesting an extra-ovarian origin. Similar to the transcriptional profile of vitellogenin, cathepsin B transcripts were shown to accumulate post-blood meal and reached their highest expression at 36 h PBM. However, while vitellogenin expression decreased drastically at 48 h PBM, the expression of the cathepsins increased until 84 h PBM, at which time the females of our colony were ready for oviposition. The similarity between their transcriptional profiles strongly suggests a role for the cathepsin B homologues in vitellin degradation.

Crystal structure of Bombyx mori arylphorins reveals a 3:3 heterohexamer with multiple papain cleavage sites

In holometabolous insects, the accumulation and utilization of storage proteins (SPs), including arylphorins and methionine-rich proteins, are critical for the insect metamorphosis. SPs function as amino acids reserves, which are synthesized in fat body, secreted into the larval hemolymph and taken up by fat body shortly before pupation. However, the detailed molecular mechanisms of digestion and utilization of SPs during development are largely unknown. Here, we report the crystal structure of Bombyx mori arylphorins at 2.8 Å, which displays a heterohexameric structural arrangement formed by trimerization of dimers comprising two structural similar arylphorins. Our limited proteolysis assay and microarray data strongly suggest that papain-like proteases are the major players for B. mori arylphorins digestion in vitro and in vivo. Consistent with the biochemical data, dozens of papain cleavage sites are mapped on the surface of the heterohexameric structure of B. mori arylphorins. Hence, our results provide the insightful information to understand the metamorphosis of holometabolous insects at molecular level.

Microscopic and molecular characterization of ovarian follicle atresia in Rhodnius prolixus Stahl under immune challenge

In this work we characterized the degenerative process of ovarian follicles of the bug Rhodnius prolixus challenged with the non-entomopathogenic fungus Aspergillus niger. An injection of A. niger conidia directly into the hemocoel of adult R. prolixus females at the onset of vitellogenesis caused no effect on host lifespan but elicited a net reduction in egg batch size. Direct inspection of ovaries from the mycosed insects revealed that fungal challenge led to atresia of the vitellogenic follicles. Light microscopy and DAPI staining showed follicle shrinkage, ooplasm alteration and disorganization of the monolayer of follicle cells in the atretic follicles. Transmission electron microscopy of thin sections of follicle epithelium also showed nuclei with condensed chromatin, electron dense mitochondria and large autophagic vacuoles. Occurrence of apoptosis of follicle cells in these follicles was visualized by TUNEL labeling. Resorption of the yolk involved an increase in protease activities (aspartyl and cysteinyl proteases) which were associated with precocious acidification of yolk granules and degradation of yolk protein content. The role of follicle atresia in nonspecific host-pathogen associations and the origin of protease activity that led to yolk resorption are discussed.

Drosophila CTLA-2-like protein (D/CTLA-2) inhibits cysteine proteinase 1 (CP1), a cathepsin L-like enzyme

In this study, we present a propeptide-like cysteine proteinase inhibitor, Drosophila CTLA-2-like protein (D/CTLA-2), a CG10460 (crammer) gene product, with an amino acid sequence significantly similar to the proregion of Drosophila cysteine proteinase 1 (CP1). Recombinant D/CTLA-2, expressed in E. coli, strongly inhibited Bombyx cysteine proteinase (BCP) with a Ki value of 4.7 nM. It also inhibited cathepsins L and H with Ki values of 3.9 (human liver) and 0.43 (rabbit liver) nM, and 7.8 nM (human liver), respectively. Recombinant D/CTLA-2 exhibited low but significant inhibitory activities to cathepsin B with Ki values of 15 nM (human liver) and 110 nM (rat liver), but hardly inhibited papain. We attempted to purify cysteine proteinases inhibited by D/CTLA-2 from total bodies of adult Drosophila. Recombinant D/CTLA-2 significantly inhibited CP1 with a Ki value of 12 nM, indicating that CP1, a cognate enzyme of D/CTLA-2, is a target enzyme of the inhibitor in Drosophila cells. These results indicate that D/CTLA-2 is a selective inhibitor of cathepsin L-like cysteine proteinases similar to other propeptide-like cysteine proteinase inhibitors such as Bombyx cysteine proteinase inhibitors (BCPI) and cytotoxic T-lymphocyte antigen-2 (CTLA-2). D/CTLA-2 was expressed over the whole life cycle of Drosophila. Strong expression was observed in the garland cells and prothoracic gland in the late stages of embryonic development. These results suggest that D/CTLA-2, implicated in intra- and extra-cellular digestive processes, functions in these tissues by suppressing uncontrolled enzymatic activities of CP1.

Dendritic and axonal localization of cytotoxic T-lymphocyte antigen-2 alpha protein in mouse brain

Cytotoxic T-lymphocyte antigen-2 alpha (CTLA-2alpha) is a novel cysteine proteinase inhibitor protein originally discovered and expressed in mouse activated T-cells and mast cells. Expressed recombinant CTLA-2alpha is shown to exhibit selective inhibition of cathepsin L-like cysteine proteinases. We have recently reported the expression pattern of CTLA-2alpha mRNA in mouse brain by in situ hybridization, demonstrating that it is mainly enriched within neuronal populations. In this study we present the distribution profile of the protein by immunohistochemical analysis. Results showed that CTLA-2alpha protein is preferentially localized in dendritic and axonal compartments. In telencephalon, strong labeling was detected in dendrites in the cerebral cortices, stratum radiatum and stratum lacunosum moleculare and within axonal fibers of stratum lucidum where mossy fibers emanating from all parts of the granule cell layer of dentate gyrus terminate at pyramidal neurons and interneurons. In diencephalon, moderate staining was found in all thalamic nuclei but was strong in medial habenular nucleus and the hypothalamic nuclei including suprachiasmatic nucleus, optic chiasm, arcuate nucleus and median eminence. In mesencephalon, strong immunoreactivity was detected in superior colliculus, inferior colliculus and paramedian raphe nucleus. In the rhombencephalon, the pontine nucleus and transverse fibers of the pons revealed strong staining but were moderate in vestibular nuclei. Strong immunoreactivity was also observed in the internal white matter, granule cell layer and Purkinje cell layer within cerebellum. On Western blot analysis, a band of 14 kDa for CTLA-2alpha from protein extracts of the cerebrum, cerebellum, pons and medulla was detected. The distribution pattern and functional considerations of CTLA-2alpha in the brain are discussed.

The Caenorhabditis elegans CPI-2a cystatin-like inhibitor has an essential regulatory role during oogenesis and fertilization

In the present study, we characterized a sterile cpi-2a(ok1256) deletion mutant in Caenorhabditis elegans and showed that CPI-2a has an essential regulatory role during oogenesis and fertilization. We have also shown that the CPI2a inhibitor and both Ce-CPL-1 and Ce-CPZ-1 enzymes are present in the myoepithelial sheath surrounding germ cells, oocytes, and embryos as well as in the yolk granules within normal oocytes. Staining of mutant worms with anti-yolk protein antibodies has indicted that the proteins are not present in the mature oocytes. Moreover, green fluorescent protein expression was absence or reduced in cpi-2a/yp170:gfp mutant oocytes, although it was expressed in one of the successfully developed embryos. Based on these results, we hypothesize that the sterility in cpi-2a(ok1256) mutant worms is potentially caused by two possible mechanisms: 1) defects in the uptake and/or processing of yolk proteins by the growing oocytes and 2) indirect induction of defects in cell-cell signaling that is critical for promoting germ line development, oocyte maturation, ovulation, and fertilization. A defect in any of these processes would have detrimental effects on the development of normal embryos and consequently normal production of progenies as we observed in cpi-2a mutant worms. This is the first study that demonstrates the expression of cysteine proteases and their endogenous inhibitor in the gonadal sheath cells surrounding germ cells and oocytes, which indirectly have established their potential involvement in proteolytic processing of molecules within the gonadal sheath cells, such as components of the extracellular matrix or the cytoskeletal proteins, which are essential for proper cell-cell signaling activities of the gonadal sheath cells during normal maturation and ovulation processes.

Kinetics of energy source utilization in Boophilus microplus (Canestrini, 1887) (Acari: Ixodidae) embryonic development

The present work evaluates the kinetics of utilization of the main potential energy sources throughout the embryonic developmental stages of Boophilus microplus. The embryonic development of this arthropod is completed in 21 days. Cellularization of the blastoderm occurs on the 6th day and is rapidly followed by germ band extension and segmentation, whose first signs are visible on the 7th day. Cellularization is typically a maternal-driven process, carried out by molecular determinants deposited in the oocyte during oogenesis. On the other hand, segmentation is of zygotic nature, being the consequence of the synthesis of various components by the growing embryo. The enhancement in total B. microplus RNA was observed after cellularization, corroborating the replacement of maternal-driven processes by embryonic zygotic expression. An abrupt increase in oxygen consumption was observed from cellularization until the 8th day of development. The reduction in dry weight at the same period and the susceptibility of oxygen consumption to KCN suggest that the respiration process is activated during early embryonic development. A marked decrease in total lipid content occurred between the 5th and 7th days of development, suggesting this is the main energy source for cellularization. A major reduction in carbohydrate content occurred later, between the 7th and 9th days, and it could be assigned to the morphological segmentation of the embryo. Although the total amount of proteins remains unchanged from oviposition to hatching, a 15% reduction in vitellin (VT) content was observed before cellularization, up to the 4th day after egglaying. This observation was correlated to the synthesis of new proteins needed to support early embryo development. Additional 20% of VT was consumed thereafter, mainly at the end of embryogenesis, and in this case VT is probably used as energy source to the older embryo. Altogether, these data indicate different energy sources for maternal and zygotic driven processes.

A homologue of cathepsin L identified in conditioned medium from Sf9 insect cells

Gelatin zymography revealed the presence of proteolytic activity in conditioned medium (CM) from a serum-free, non-infected Spodoptera frugiperda, Sf9 insect cell culture. Two peptidase bands at about 49 and 39 kDa were detected and found to be proform and active form of the same enzyme. The 49-kDa form was visible on zymogram gels in samples of CM taken on days 4 and 5 of an Sf9 culture, while the 39-kDa form was seen on days 6 and 7. On basis of the inhibitor profile and substrate range, the enzyme was identified as an Sf9 homologue of cathepsin L, a papain-like cysteine peptidase. After lowering the pH of Sf9 CM to 3.5, an additional peptidase band at 22 kDa appeared. This peptidase showed the same inhibitor profile, substrate range and optimum pH (5.0) as the 39-kDa form, indicating that Sf9 cathepsin L has two active forms, at 39 and 22 kDa. Addition of the cysteine peptidase inhibitor E-64c to an Sf9 culture inhibited all proteolytic activities of Sf9 cathepsin L but did not influence the proliferation of Sf9 cells.

Cathepsin D-mediated yolk protein degradation is blocked by acid phosphatase inhibitors

Vitellin (VT) is a lipoglycophosphoprotein stored inside the eggs of every oviparous organism during oogenesis. In the blood-sucking bug Rhodnius prolixus, VT is deposited inside growing oocytes together with two acid hydrolases: acid phosphatase (AP) and cathepsin D (CD). Egg fertilization triggers AP activity and VT proteolysis in vivo [Insect Biochem. Mol. Biol. 2002 (32) 847]. Here, we show that CD is the main protease targeting VT proteolysis during egg development. CD activity in total egg homogenates is blocked by the classical aspartyl protease inhibitor, pepstatin A. Surprisingly, AP inhibitors such as NaF, Na+/K+ tartrate, and inorganic phosphate also block VT proteolysis, whereas this effect is not observed when tyrosine phosphatase inhibitors such as vanadate and phenylarsine oxide or an inhibitor of alkaline phosphatases such as levamisole are used in a VT proteolysis assay. NaF concentrations that block isolated AP activity do not affect the activity of partially purified CD. Therefore, a specific repressor of VT proteolysis must be dephosphorylated by AP in vivo. In conclusion, these results demonstrate for the first time that acid hydrolases act cooperatively to promote yolk degradation during egg development in arthropods.

Activity and sequence characterization of two cysteine proteases in the digestive tract of the reduviid bug Triatoma infestans

Cathepsin B- and cathepsin L-like activities were identified in gut extracts of the blood-sucking bug Triatoma infestans using specific substrates and inhibitors. Activities decreased during the first 2 days after feeding but increased to a maximum value at 5 and 10 days post feeding. The deduced 332 and 328 amino acid sequences showed high levels of identity (50-60%) to other insect cathepsin B- and L-like proteases, respectively. The three amino acid residues of the catalytic domain, CHN, and the GCNGG motif were conserved in both cathepsins, but the occluding loop, characterizing B-like cathepsins, was present only in one. ERFNIN and GNFD motifs occurred in the other sequence, defining it as cathepsin L-like. The cathepsin B-like gene was expressed at low, constitutive levels in unfed and fed T. infestans.

Cathepsin L protease (CPL-1) is essential for yolk processing during embryogenesis in Caenorhabditis elegans

Cysteine proteases are involved in the degradation of intracellular and extracellular proteins, although their precise roles in vivo are not well understood. Here we characterise a genetic mutant of the Caenorhabditis elegans cathepsin L protease gene cpl-1. CPL-1 is provided maternally and is essential for C. elegans embryogenesis. Immunofluorescence and electron microscopy data show that yolk endocytosis and initial yolk platelet formation occur normally in cpl-1 mutant oocytes and embryos. However, at around the 8-12 cell stage of embryogenesis, yolk platelets begin to aggregate and these enlarged yolk platelets fill the cytoplasm of cpl-1 mutant embryos. Coincident with this aggregation is loss of fluorescence from a yolk green fluorescent protein (YP170::GFP). This suggests that loss of CPL-1 activity leads to aberrant processing and/or conformational changes in yolk proteins, resulting in abnormal platelet fusion. This study has relevance to the abnormal fusion and aggregation of lysosomes in cathepsin L-deficient mice and to other lysosomal disorders.

Proteolytic activity of Boophilus microplus Yolk pro-Cathepsin D (BYC) is coincident with cortical acidification during embryogenesis

In a previous report (Parasitology 116 (1998) 525) we isolated and characterized Boophilus Yolk pro-Cathepsin (BYC), an aspartic proteinase precursor from the eggs of the hard tick. The present study was designed to characterize the function of BYC in the consumption of vitellin (VT), the major yolk protein, during embryogenesis. Both purified BYC and total egg homogenate proteolytic activity showed a similar pH dependence profile with an acidic optimum. Purified BYC presented higher activity against VT as a substrate when compared to other proteins. The VT degradation pattern observed in vitro also showed a similar profile to that observed in vivo. Co-localization of BYC and acidic cortical yolk granules was performed by immunocytochemistry and confocal microscopy. Proton-pumping activity of yolk granules in vitro was higher in eggs collected 4 day after oviposition than in newly laid eggs. Taken together, our data suggest that BYC plays a major role in the degradation of VT and that its activity is controlled by acidification of yolk platelets localized at the cortical cytoplasm of the developing Boophilus microplus egg.

Vitellin cleavage products are proteolytically degraded by ubiquitination in stick insect embryos

Vitellin polypeptides are proteolytically processed in ovarian follicles and embryos of the stick insect Carausius morosus. Data show that vitellin polypeptide A(3) of 54kDa is processed to yield polypeptide A(3)(*) of about 48kDa upon completion of ovarian development, whereas vitellin polypeptide A(2) of 90kDa yields polypeptide E(9) during embryonic development. As vitellin polypeptides are processed, polypeptides A(3)(*) and E(9) are transferred from the yolk granules to the cytosolic space of the vitellophages and start to express a ubiquitin reactivity. At the confocal microscope, anti-ubiquitin antibodies label specifically numerous small yolk granules and the cytosolic space of vitellophages. During embryonic development, ubiquitin carrying granules undergo acidification in much the same way as larger yolk granules. However, only these latter organelles are capable of converting a latent cysteine pro-protease into an active yolk protease upon acidification of their luminal space. These data are interpreted as indicating that ubiquitin-like polypeptides are restricted to small granules throughout ovarian and embryonic development, and that vitellin cleavage products are ubiquitinated following acidification of large yolk granules and transfer to the cytosolic space of the vitellophages.

In vivo activation of pro-form Bombyx cysteine protease (BCP) in silkmoth eggs: localization of yolk proteins and BCP, and acidification of yolk granules

The present study was designed to investigate the process of acidification of yolk granules during embryogenesis. In oocytes of mature Bombyx mori silkmoth, yolk proteins and a cysteine protease (pro-form BCP) were found in yolk granules. BCP was localized in small sized yolk granules (SYG, 3-6 microm in diameter) and yolk proteins in large sized granules (LYG, 6-11 microm in diameter), which might result in a spatial separation of protease and its substrates to avoid unnecessary hydrolysis. The granules were isolated on Percoll density gradient centrifugation. Although separation of LYG and SYG was incomplete, the granules sedimented in different fractions when using unfertilized egg extract, in which LYG was recovered from heavier fractions and BCP from lighter fractions. Acid phosphatase, as well as other lysosomal marker enzymes tested, was recovered from LYG-containing fractions. When extracts were prepared from developing eggs (day 3), some BCP-containing granules co-sedimented with LYG. The inactive pro-form BCP was activated in vivo, in parallel with yolk protein degradation, and as demonstrated previously in vitro under acidic conditions (). These results suggest that acidification occurs in yolk granules during embryogenesis. This was also confirmed using acridine orange fluorescent dye. In early development, most yolk granules were neutral, but became acidic during embryonic development. SYG were progressively recovered in heavier density fractions, displaying acidic interior. In this fraction, BCP-containing granules seem to be associated with larger granules (6-11 microm in size). In addition, SYG (BCP containing granules) were likely to be acidified earlier than LYG. Our results suggest that acidification initiates yolk degradation through activation of pro-form BCP.

Changes in cysteine protease activity and localization during midgut metamorphosis in the crucifer root maggot (Delia radicum)

We show that differential localization and/or activation of two cysteine protease activities occur at the onset of dipteran midgut metamorphosis. A 26 kDa cysteine protease activity was associated specifically with midgut tissues of late third instar larvae. Starvation of mid third instar larvae simulated the onset of prepupation and resulted in loss of the 26 kDa protease activity. A cDNA clone encoding a cysteine protease, termed DrCP1, was isolated and shown to be highly similar to those from Sarcophaga peregrina and Drosophila melanogaster (DmCP1). DrCP1 mRNA was present in all developmental stages including eggs, larvae, pupae and adults, but was highly induced at the onset of the larval-pupal transition and thereafter. The DrCP1 protein is localized to the exterior of the midgut tissues during the onset of the prepupal transition period, possibly in response to ecdysone. Analysis of transcription factor binding sites associated with the DmCP1 promoter indicated that elements exist that allow for both ecdysone-mediated as well as tissue-specific regulation. Based upon these and other studies we propose: (1) that the expression, activity and localization of the DrCP1-like cysteine proteases are highly regulated throughout development; and, (2) that cysteine protease activities are involved in aspects of tissue reconstruction at the onset of and during metamorphosis.

Absorption, transportation and digestion of egg white in quail embryos

The present study was done to reveal how egg white is taken up by embryonic tissues, the pathway through which egg white is transported, and the location where it is digested during the development of the quail Coturnix japonica. Antiserum against quail ovalbumin was raised in rabbit and used as a probe. By immunoelectron microscopy, the uptake of ovalbumin on a small scale by receptor-mediated endocytosis was observed in the ectodermal cells of the yolk sac on days four to seven of incubation. The uptake of egg white on a large scale by fluid-phase endocytosis took place in the cells generally referred to collectively as the 'albumen sac'. The ovalbumin was transported through the albumen sac into the extraembryonic cavity during days eight to 10, and then into the amniotic cavity through the amnion approximately on day 10. Ovalbumin was present in the intestinal lumen on days 11 and 14, but it was not digested in the intestinal epithelial cells. The ovalbumin was detected in the yolk of embryos after day 10. Immunoblot testing, as well as a fluoroimmunoassay, revealed that the location where the amount of ovalbumin was highest changed chronologically from the extraembryonic cavity on day 10 to the amniotic cavity on day 11, the intestinal lumen on day 12 and then to the yolk on day 13. Several low molecular proteins which cross-reacted with the antiserum were observed in the extracts of the yolk. The reaction producing these proteins depended on low pH (approximately 3.0) and was inhibited by pepstatin A. The ovotransferrin was similarly digested. These results indicate that egg white is, for the most part, transported through the albumen sac to the yolk via the extraembryonic cavity, the amniotic cavity, and the intestinal lumen, and is digested in the yolk by aspartic proteinases.

Maturation of barley cysteine endopeptidase expressed in Trichoderma reesei is distorted by incomplete processing

Maturation of barley cysteine endopeptidase B (EPB) in Trichoderma reesei was studied with metabolic in hibitors, Western blotting, and immuno microscopy. The inactive 42-kDa recombinant EPB proprotein, first detected in apical cells, was sequentially processed in a time-dependent manner to a secreted polypeptide of 38.5 kDa, and thereafter, to polypeptides of 37.5, 35.5, and 32 kDa exhibiting enzyme activity both in the hyphae and culture medium. The sizes of the different forms of recombinant EPB were in accordance with molecular masses calculated from the deduced amino acid sequence, assuming cleavage at four putative Kex2p sites present in the 42-kDa proprotein. Both the liquid and the zymogram in-gel activity assays indicated that the 32-kDa enzyme produced in T. reesei in vivo was 2 kDa larger and four times less active than the endogenous EPB. Brefeldin A treatment prevented the last Kex2p processing step of EPB from a 35.5- to a 32-kDa protein. This coincided with a significant increase in the immuno-gold label for EPB and in modified Golgi-like bodies, which suggests that the processing step probably took place in medial Golgi. A 30.5-kDa EPB polypeptide was observed when glycosylation was inhibited by tunicamycin (TM) or when deglycosylation was carried out enzymatically. Deglycosylation increased the enzyme activity twofold, which was also indicated by an increased fluorescence by TM treatment in the zymogram in-gel activity assay. Simultaneous incubation with TM and monensin produced a peptide of 31.5 kDa. Therefore, monensin may inhibit the final processing step of an unglycosylated EPB by an unknown protease in the fungus. In any case, the final recombinant EPB product in Trichoderma differs from the mature endogenous 30-kDa enzyme produced in barley.

Cathepsin L is essential for embryogenesis and development of Caenorhabditis elegans

Cysteine proteases play critical biological roles in both intracellular and extracellular processes. We characterized Ce-cpl-1, a Caenorhabditis elegans cathepsin L-like cysteine protease. RNA interference with Ce-cpl-1 activity resulted in embryonic lethality and a transient delayed growth of larvae to egg producing adults, suggesting an essential role for cpl-1 during embryogenesis, and most likely during post-embryonic development. Cpl-1 gene (Ce-cpl-1:lacZ) is widely expressed in the intestine and hypodermal cells of transgenic worms, while the fusion protein (Ce-CPL-1::GFP) was expressed in the hypodermis, pharynx, and gonad. The CPL-1 native protein accumulates in early to late stage embryos and becomes highly concentrated in gut cells during late embryonic development. CPL-1 is also present near the periphery of the eggshell as well as in the cuticle of larval stages suggesting that it may function not only in embryogenesis but also in further development of the worm. Although the precise role of Ce-CPL-1 during embryogenesis is not yet clear it could be involved in the processing of nutrients responsible for synthesis and/or in the degradation of eggshell. Moreover, an increase in the cpl-1 mRNA is seen in the intermolt period approximately 4 h prior to each molt. During this process Ce-CPL-1 may act as a proteolytic enzyme in the processing/degradation of cuticular or other proteins. Similar localization of a related cathepsin L in the filarial nematode Onchocerca volvulus, eggshell and cuticle, suggests that some of the Ce-CPL-1 function during development may be conserved in other parasitic nematodes.

A heme-binding aspartic proteinase from the eggs of the hard tick Boophilus microplus

An aspartic proteinase that binds heme with a 1:1 stoichiometry was isolated and cloned from the eggs of the cattle tick Boophilus microplus. This proteinase, herein named THAP (tick heme-binding aspartic proteinase) showed pepstatin-sensitive hydrolytic activity against several peptide and protein substrates. Although hemoglobin was a good substrate for THAP, low proteolytic activity was observed against globin devoid of the heme prosthetic group. Hydrolysis of globin by THAP increased as increasing amounts of heme were added to globin, with maximum activation at a heme-to-globin 1:1 ratio. Further additions of heme to the reaction medium inhibited proteolysis, back to a level similar to that observed against globin alone. The addition of heme did not change THAP activity toward a synthetic peptide or against ribonuclease, a non-hemeprotein substrate. The major storage protein of tick eggs, vitellin (VT), the probable physiological substrate of THAP, is a hemeprotein. Hydrolysis of VT by THAP was also inhibited by the addition of heme to the incubation media. Taken together, our results suggest that THAP uses heme bound to VT as a docking site to increase specificity and regulate VT degradation according to heme availability.

Bombyx acid cysteine protease (BCP): hormonal regulation of biosynthesis and accumulation in the ovary

We previously reported purification of the cysteine protease from Bombyx eggs (BCP) and the occurrence of the enzyme in various tissues of this insect. In the present paper, we present a detailed analysis of stage-specific changes in activity of BCP between the fourth larval instar and pupal-adult development. A synthetic fluorescent peptide, carbobenzoxy-L-Phenylalanyl-L-Arginine4-methylcoumaryl-7-amide (Z-Phe-Arg-MCA), was used to assay proteolytic activity. When tissue extracts were treated with anti-BCP serum before assay of enzyme activity, most activity towards Z-Phe-Arg-MCA was removed from the extracts. Therefore proteolytic activity in the present experiments is due mainly to BCP. We used Western blot and Northern blot analyses to determine tissue and stage specific expression of the enzyme. In the 5th larval fat body and hemolymph, BCP activity dramatically increased at the time of spinning, returning to the basal level before ecdysis. Northern blot analysis showed that a 1.5 kilobase mRNA which hybridizes to BCPcDNA suddenly appears during this period. Similar results were obtained in 4th instar fat body. In pupal hemolymph and fat body, low basal activity of BCP was detected early (day 0 to day 3 after pupal ecdysis), followed by a pronounced increase to a maximum six days after ecdysis, before returning to the basal level. In ovariectomized female pupae, a significant amount of proteolytic activity accumulated in hemolymph, suggesting that the enzyme is synthesized in the fat body and transferred into the ovary along with vitellogenin. BCP activity increased three days after injection of 20-hydroxyecdysone into ligated pupae. Furthermore, putative BCPmRNA appeared in the fat body within 24 hours after injection. This increase was completely blocked by the administration of cycloheximide. The results suggest that, BCP is synthesized in extraovarian tissues such as fat body and ovarian follicle cells and accumulates in the ovary, thus representing a new class of yolk protein.

Proregion of Bombyx mori cysteine proteinase functions as an intramolecular chaperone to promote proper folding of the mature enzyme

A cDNA encoding the proform of Bombyx cysteine proteinase (BCP) was expressed at a high level in Escherichia coli using the T7 polymerase expression system. The insoluble recombinant zymogen was solubilized and renatured by modifying a method applied to human pro-cathepsin L. Like the natural BCP precursor, the recombinant proenzyme was spontaneously converted to an active proteinase at pH 3.75. A deletion in the central region of the propeptide resulted in much loss of the activity, suggesting that the propeptide is essential for proper folding during renaturation. In contrast, the renatured mature form of recombinant BCP was not active but regained activity by including the propeptide in the renaturing buffer, suggesting that the propeptide, acting as an intramolecular chaperone, promotes refolding of the associated proteinase domain into an active conformation. The mature form of natural BCP rapidly lost its activity at neutral pH, whereas its proform was stable. The mature enzyme retained some activity in the presence of the propeptide. Arch.

Purification and characterization of Bombyx cysteine proteinase specific inhibitors from the hemolymph of Bombyx mori

Protein inhibitors capable of inhibiting BCP (Bombyx cysteine proteinase) were found in the larval-pupal hemolymph of Bombyx mori. Two forms of the inhibitors, named BCPI (BCP inhibitor) alpha and BCPI beta, were purified from the pupal hemolymph by heat treatment and column chromatographies on CM-cellulose, Toyopearl HW-50, Phenyl-Sepharose, and Mono Q. Purified BCPI beta gave a single protein band with a molecular mass of 10,500 daltons on SDS-PAGE. BCPI alpha is mostly composed of the same molecular mass protein as BCPI beta. Both forms were inhibitory towards other cysteine proteinases such as cathepsins L,B and papain but had no effects on trypsin and pepsin. Both forms inhibited the processing of the enzymatically inactive proform of BCP (pro-BCP) to the activated mature BCP. BCPI alpha and BCPI beta shared many other features such as molecular mass determined by gel filtration, antigenicity, and HPLC profiles. NH(2)-terminal amino acid sequencing of the purified inhibitors revealed that three amino acid residues were different in the BCPI alpha and BCPI beta sequences, all others being identical. The hemolymph BCP inhibitor increased activity approximately four- to fivefold at the time of spinning and maintained this level of activity during pupation.

Mosquito cathepsin B-like protease involved in embryonic degradation of vitellin is produced as a latent extraovarian precursor

Here we report identification of a novel member of the thiol protease superfamily in the yellow fever mosquito, Aedes aegypti. It is synthesized and secreted as a latent proenzyme in a sex-, stage-, and tissue-specific manner by the fat body, an insect metabolic tissue, of female mosquitoes during vitellogenesis in response to blood feeding. The secreted, hemolymph form of the enzyme is a large molecule, likely a hexamer, consisting of 44-kDa subunits. The deduced amino acid sequence of this 44-kDa precursor shares high similarity with cathepsin B but not with other mammalian cathepsins. We have named this mosquito enzyme vitellogenic cathepsin B (VCB). VCB decreases to 42 kDa after internalization by oocytes. In mature yolk bodies, VCB is located in the matrix surrounding the crystalline yolk protein, vitellin. At the onset of embryogenesis, VCB is further processed to 33 kDa. The embryo extract containing the 33-kDa VCB is active toward benzoyloxycarbonyl-Arg-Arg-para-nitroanilide, a cathepsin B-specific substrate, and degrades vitellogenin, the vitellin precursor. Both of these enzymatic activities are prevented by trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane (E-64), a thiol protease inhibitor. Furthermore, addition of the anti-VCB antibody to the embryonic extract prevented cleavage of vitellogenin, strongly indicating that the activated VCB is involved in embryonic degradation of vitellin.

A novel egg-derived tyrosine phosphatase, EDTP, that participates in the embryogenesis of Sarcophaga peregrina (flesh fly)

We have previously reported that cathepsin L mRNA is present in unfertilized eggs of Sarcophaga peregrina (flesh fly) as a maternal mRNA, which suggests that cathepsin L is required for embryogenesis. Now we have identified an egg protein, with a molecular mass of 100 kDa, that is extremely susceptible to cathepsin L digestion and which disappears rapidly as the embryos develop. We purified this protein to homogeneity, cloned its cDNA, and found that it contained a consensus sequence for the active site of tyrosine phosphatase. In fact this protein showed tyrosine phosphatase activity, indicating that it is a novel tyrosine phosphatase. The expression and subsequent disappearance of this protein, which we have named egg-derived tyrosine phosphatase (EDTP), may be indispensable for embryogenesis of Sarcophaga.

Cysteine proteinase plays a key role for the initiation of yolk digestion during development of Xenopus laevis

In electrophoretic analyses, extracts of Xenopus laevis neurulae exhibited activities digesting yolk proteins maximally at pH 4.8. These activities were completely inhibited by a mixture of pepstatin A and Z-Phe-Phe-CHN2, thus being identifiable as cathepsin D and cysteine proteinase. The electrophoretic profiles of yolk proteins cleaved by embryonic extracts changed at gastrula stages; the profile before stage 13 was the same as that given by cathepsin D treatment and the profile at stage 13 was a combination of the profile given by cathepsin D treatment and that given by cysteine proteinase treatment. Quantitative measurement of enzyme activities showed that the cathepsin D activity that was preserved from the beginning of development increased from stages 13 to 25 and decreased thereafter, whereas the cysteine proteinase activity appeared at stage 13, gradually increased until stage 35 and strongly increased thereafter. Immunoblot analyses showed that the 43 kDa form of cathepsin D was processed to its 36 kDa form, presumably by cysteine proteinase. This change can explain the increase of cathepsin D activity at stage 13 and thereafter. Immunofluorescent staining with the antibody against cysteine proteinase occurred in mesodermal and ectodermal cells other than neural ones at stages 13-24, and in the endodermal cells at stages 24-36. Faint staining in the neural ectoderm persisted from stages 18 to 36. Immunoelectron microscope observation showed that what stained was the superficial layer of yolk platelets. All these results indicate that cysteine proteinase plays a key role in the initiation of yolk digestion during embryonic development.

Vitellin processing and protein synthesis during cricket embryogenesis

At the start of insect embryogenesis most of the protein mass of the egg cytoplasm exists as vitellin (Vt) obtained endocytically during vitellogenesis. Of the new embryo polypeptides (EP) appearing in the egg during embryogenesis, many are synthesized de novo, while, in some species, others derive from developmentally programmed partial proteolysis of Vt. Earlier we showed that by the end of vitellogenesis the two native Vts in Acheta domesticus exist in opposing gradients along the longitudinal axis of the egg. Here we hypothesize that this ooplasmic Vt distribution presents a milieu for Vt processing out of which region-specific regulatory molecules could arise. The metabolic origin and stage-specific patterns of seven predominant EPs (EP 1-7) identified by SDS-PAGE were examined and the results correlated with developmental morphology during the 14 days of embryogenesis. Based on antibody reactivity, peptide mapping and in vitro radiolabeling, we determined that EPs 1-3, 6 and 7 are Vt-derived, while EPs 4 and 5 are produced de novo by the embryo. The five Vt-derived EPs appear during the first 24 h of embryogenesis when migrating cleavage nuclei and associated cytoplasm form the cellular blastoderm, and levels of EPs 4 and 5 increase during days 4-6 of embryogenesis when katatrepsis and yolk mass contraction occur. Positive periodic acid-Schiff staining indicated that EPs 1-3 and their Vt-precursor polypeptides are glycoproteins. This work shows that developmental stage-specific Vt processing occurs during A. domesticus embryogenesis and points next to investigation of the functional significance of Vt cleavage products during development.

Purification and properties of embryonic cysteine proteinase which participates in yolk-lysis of Xenopus laevis

The study reported here aimed to purify a cysteine proteinase from neurula embryos of Xenopus laevis, since this enzyme was thought to be involved in yolk-lysis in developing embryos. The purification procedure consisted of fractionation of an embryonic extract by means of 30-90% ammonium sulfate, chromatography on diethylaminoethyl cellulose and carboxymethyl cellulose, gel filtration on Sephadex G-75 and affinity chromatography on concanavalin A-agarose. The purified enzyme had a molecular weight of 30 kDa according to both SDS-PAGE and Sephadex G-75 gel-filtration and an optimum pH of 5.5, and it preferentially cleaved the synthetic substrate, Z-Phe-Arg-MCA. Its activity was inhibited by Z-Phe-Phe-CHN2, a specific cathepsin L inhibitor, as well as by leupeptin and E-64. The NH2-terminal amino acid sequence of the enzyme was similar to that of chicken cathepsin B. These characteristics indicate that the purified enzyme is a member of the cysteine proteinase family. The antibody raised against the purified enzyme specifically stained a 30 kDa protein of neurula embryo extracts on immunoblot tests. The enzyme effectively digested Xenopus yolk proteins when the NaCl concentration in test solutions was 0.2 M. It was also confirmed that cysteine proteinase inhibitors inhibited yolk-lysis by the enzyme.

Cysteine proteinase 1 (CP1), a cathepsin L-like enzyme expressed in the Drosophila melanogaster haemocyte cell line mbn-2

We have isolated cDNA clones encoding the full-length Drosophila melanogaster cysteine proteinase 1 (CP1). The clones were isolated from the Drosophila melanogaster haemocytic mbn-2 cell line, where the gene is relatively strongly expressed, giving a transcript of 1.6 kb in size. We present the sequence encoding the full-length protein, and deduced the genomic organization of the gene by comparison to previously published genomic partial sequence data. Immunofluorescence shows that CP1 is localized in small granules, probably lysosomes, in mbn-2 cells. The data presented suggest a role for cysteine proteinase in immune functions in insects. It is likely to participate in the degradation of internalized material in phagocytic cells.

Processing of procathepsin from Musca domestica eggs

The major source of amino acids for insect embryos are yolk proteins which accumulate in developing oocytes and are hydrolyzed during embryogenesis. Studies on Musca domestica embryogenesis indicated that a cathepsin B-like proteinase is responsible for yolk protein degradation (Ribolla et al., 1993). In this study, we report the purification of mature cathepsin and show that it is made up of a single 41 kDa polypeptide chain. The Musca domestica cathepsin NH2-terminal 11-residue sequence was determined (Ala-Pro-Lys-Tyr-Val-Asp-Tyr-Gly-Glu-Asn-Glu) and reveals homology with other cathepsins of the papain family. Experiments using serum anti-cathepsin show that the enzyme is stored in oocytes as a 55 kDa zymogen. The activation of the zymogen occurs in vitro only at low pH. In vitro activation in the presence of cysteine protease inhibitors is blocked at an intermediary polypeptide of 48 kDa. Kinetic studies of this activation process at pH 3.5 and 4.6 show that the zymogen is processed in a manner similar to that of pepsin (Foltmann, 1986) and papain (Vernet et al., 1991). We propose that Musca domestica cathepsin zymogen activation occurs in two steps. First, an intramolecular cleavage of the procathepsin polypeptide chain (55,000), induced by low pH gives rise to an intermediary polypeptide (48,000) which then undergoes autolysis to produce the mature enzyme (41,000).

Vitreous and aqueous humors contain a latent proteinase activity that abolishes IGF binding to specific IGF binding proteins

Several distinct insulin-like growth factor binding proteins (IGFBPs) are present in tissues and fluids of the developing and adult eye. However, the mechanism(s) involved in the regulation of ocular IGFBP levels is unknown. We have now identified an endogenous factor in vitreous and aqueous humors that, when activated by sodium dodecyl sulfate (SDS), abolishes the capacity of specific low molecular weight IGFBPs (i.e. 24-30 kDa) to bind IGF as assessed by western ligand blotting. In contrast, IGF binding to the 46 and 32 kDa IGFBPs (IGFBP-3 and IGFBP-2 respectively) is not affected by the SDS-activated inhibitory factor (IF). Maximal activation of the IF occurs at an SDS concentration of approximately 0.015%. Incubations in the presence of the serine-proteinase inhibitor aprotinin result in marked inhibition of IF activity. Preliminary characterization by ultrafiltration suggests that the IF is large (< 100 kDa) and/or that it is present in a complex. The finding of a factor, most likely a serine proteinase, that specifically abolishes IGF binding to low molecular weight IGFBPs suggests a mechanism for regulating the levels of these IGFBPs and thus the functional activities of IGFs in ocular fluids under normal and/or pathological conditions.