Regulation of Proteolytic Activity to Improve the Recovery of Macrobrachium rosenbergii Nodavirus Capsid Protein

The causative agent of white tail disease (WTD) in the giant freshwater prawn is Macrobrachium rosenbergii nodavirus (MrNV). The recombinant capsid protein (CP) of MrNV was previously expressed in Escherichia coli, and it self-assembled into icosahedral virus-like particles (VLPs) with a diameter of approximately 30 nm. Extensive studies on the MrNV CP VLPs have attracted widespread attention in their potential applications as biological nano-containers for targeted drug delivery and antigen display scaffolds for vaccine developments. Despite their advantageous features, the recombinant MrNV CP VLPs produced in E. coli are seriously affected by protease degradations, which significantly affect the yield and stability of the VLPs. Therefore, the aim of this study is to enhance the stability of MrNV CP by modulating the protease degradation activity. Edman degradation amino acid sequencing revealed that the proteolytic cleavage occurred at arginine 26 of the MrNV CP. The potential proteases responsible for the degradation were predicted in silico using the Peptidecutter, Expasy. To circumvent proteolysis, specific protease inhibitors (PMSF, AEBSF and E-64) were tested to reduce the degradation rates. Modulation of proteolytic activity demonstrated that a cysteine protease was responsible for the MrNV CP degradation. The addition of E-64, a cysteine protease inhibitor, remarkably improved the yield of MrNV CP by 2.3-fold compared to the control. This innovative approach generates an economical method to improve the scalability of MrNV CP VLPs using individual protease inhibitors, enabling the protein to retain their structural integrity and stability for prominent downstream applications including drug delivery and vaccine development.

Localization and enzyme kinetics of aminopeptidase N3 from Toxoplasma gondii

Aminopeptidase N is an important metalloenzyme from the M1 zinc metallopeptidase family, which is present in numerous apicomplexan parasites, including Plasmodium, Eimeria, and Cryptosporidium. Aminopeptidase N is a potential drug target, and hence, its properties have been widely investigated. In the current study, the cellular localization and enzyme characteristics of Toxoplasma gondii aminopeptidase N3 (TgAPN3) were evaluated in vitro. Cellular localization analysis revealed that TgAPN3 and GRA protein were co-located in the organelle and parasitophorous vacuole of T. gondii. The secretion assay showed that TgAPN3 could be co-secreted from the tachyzoites with GRA protein. A functional recombinant Toxoplasma aminopeptidase N3 (rTgAPN3) was produced in Escherichia coli. The enzyme activity was first determined using a fluorogenic H-Ala-MCA substrate. Some activity of rTgAPN3 was observed between pH 3.0 and 8.0, with a peak at pH 7.0. The activity was significantly enhanced in the presence of Co²⁺ ions. Substrate specificity of rTgAPN3 was then evaluated. The enzyme showed a preference for substrates containing N-terminal Ala residues, followed by Tyr and Cys. The rTgAPN3 activity was significantly inhibited by bestatin and phebestatin. In general, TgAPN3 was a structurally conserved member of the M1 family, although it also displayed unique biochemical characteristics. These results lay the foundation for a functional study of TgAPN3 and constitute its putative identification as a drug target.

An unusual thermostable aspartic protease from the latex of Ficus racemosa (L.)

The most extensively studied ficins have been isolated from the latex of Ficus glabrata and Ficus carica. However the proteases (ficins) from other species are less known. The purification and characterization of a protease from the latex of Ficus racemosa is reported. The enzyme purified to homogeneity is a single polypeptide chain of molecular weight of 44,500+/-500Da as determined by MALDI-TOF. The enzyme exhibited a broad spectrum of pH optima between pH 4.5-6.5 and showed maximum activity at 60+/-0.5 degrees C. The enzyme activity was completely inhibited by pepstatin-A indicating that the purified enzyme is an aspartic protease. Far-UV circular dichroic spectra revealed that the purified enzyme contains predominantly beta-structures. The purified protease is thermostable. The apparent T(m), (mid point of thermal inactivation) was found to be 70+/-0.5 degrees C. Thermal inactivation was found to follow first order kinetics at pH 5.5. Activation energy (E(a)) was found to be 44.0+/-0.3kcal mol(-1). The activation enthalpy (DeltaH *), free energy change (DeltaG *) and entropy (DeltaS *) were estimated to be 43+/-4kcal mol(-1), -26+/-3kcal mol(-1) and 204+/-10cal mol(-1)K(-1), respectively. Its enzymatic specificity studied using oxidized B chain of insulin indicates that the protease preferably hydrolyzed peptide bonds C-terminal to glutamate, leucine and phenylalanine (at P1 position). The broad specificity, pH optima and elevated thermal stability indicate the protease is distinct from other known ficins and would find applications in many sectors for its unique properties.

Lysophosphatidylcholine acyltransferase activity in Saccharomyces cerevisiae: regulation by a high-affinity Zn2+ binding site

Saccharomyces cerevisiae cells were demonstrated to contain lysophosphatidylcholine (lysoPtdCho) acyltransferase (E.C. 2.3.1.23) activity. The enzyme displayed Km(app) of 69 microM for lysoPtdCho and 152 microM for oleoyl CoA. Enzyme activity was not affected by the addition of 1 mM Mg2+, Mn2+, Ca2+, or 200 mM EDTA. However, Zn2+ inhibited lysoPtdCho acyltransferase activity to 33% control values at 0.1 mM and to 7% at 1.0 mM Zn2+. To further explore the possibility that lysoPtdCho acyltransferase may contain a high-affinity Zn2+ binding site, we tested the strong Zn2+ chelator o-phenanthroline for its ability to inhibit enzyme activity. LysoPtdCho acyltransferase activity was inhibited to 18 and 27%, respectively, those of control values in the presence of 2 and 1 mM o-phenanthroline, implying that a high-affinity Zn2+ binding site exists in lysoPtdCho acyltransferase or in an accessory protein that is essential for protein stability and/or activity. Saccharomyces cerevisiae lysoPtdCho acyltransferase activity displayed a broad lysoPtdCho fatty acyl chain substrate specificity utilizing lysoPtdCho molecules ranging in length from C10-C20 (the entire range tested). In addition, the enzyme was capable of using the ether-linked analog of lysoPtdCho, 1-O-alkyl-2-hydroxy-sn-3-glycerophosphocholine, as a substrate. The ability of S. cerevisiae to incorporate radiolabeled 1-O-alkyl-2-hydroxy-sn-3-glycerophosphocholine into phosphatidylcholine in vitro was exploited to demonstrate a direct precursor-product relationship between lysoPtdCho molecules and their incorporation into phosphatidylcholine in vivo. Identical labeling results were obtained in S. cerevisiae cells disrupted for their major transacylase activity, PLB1, demonstrating that the incorporation of lysolipid was via acyltransferase, and not transacylase, activity.

Effects of the cys mutations on structure and function of the ATP-dependent HslVU protease in Escherichia coli. The Cys287 to Val mutation in HslU uncouples the ATP-dependent proteolysis by HslvU from ATP hydrolysis

To define the role of the Cys residues in the ATP-dependent HslVU protease, mutagenesis was performed to replace either Cys261 or Cys287 in HslU with Val and Cys159 in HslV with Ser or Ala. Whereas HslU/C261V could hydrolyze ATP and support the ATP-dependent proteolytic activity of HslV as well as the wild-type HslU, HslU/C287V could not hydrolyze ATP. Nevertheless, HslU/C287V could support the HslV-mediated proteolysis by forming the HslVU complex in the presence of ATP but not its absence, indicating that ATP binding but not its hydrolysis is essential for proteolysis. Whereas treatment of N-ethylmaleimide (NEM) resulted in dissociation of the oligomeric HslU into monomers, the C261V mutation, but not C287V, prevented the NEM effect. These results suggest that Cys261 is involved in oligomerization and that Cys287 is related to the ATPase function of HslU. NEM also dissociated the dodecameric HslV into monomers, and this effect could be prevented by either the C159S or C159A mutation, suggesting the involvement of Cys159 in oligomerization of HslV. Moreover, either mutation abolished both the basal and HslU-activated proteolytic activity of HslV and its ability to activate the HslU ATPase and to form the HslVU complex, indicating that Cys159 is essential for the proteolytic activity of HslV and its interaction with HslU. These results suggest that the Cys residues play an important role in maintaining the structure and function of the HslVU protease.

ATP binding, but not its hydrolysis, is required for assembly and proteolytic activity of the HslVU protease in Escherichia coli

HslVU is an ATP-dependent protease consisting of two multimeric components: the HslU ATPase and the HslV peptidase. To gain an insight into the role of ATP hydrolysis in protein breakdown, we determined the insulin B-chain-degrading activity and assembly of HslVU in the presence of ATP and its nonhydrolyzable analogs. While beta,gamma-methylene-ATP could not support the proteolytic activity, beta,gamma-imido-ATP supported it to an extent less than 10% of that seen with ATP. Surprisingly, however, HslVU degraded insulin B-chain even more rapidly in the presence of ATPgammaS than with ATP. Furthermore, the ability of ATP and its analogs in supporting the proteolytic activity was closely correlated with their ability in supporting the oligomerization of HslU and the formation of the HslVU complex. However, ADP, which is capable of supporting the HslU oligomerization, could not support the HslVU complex formation or the proteolytic activity, suggesting that the conformation of the ADP-bound HslU oligomer is different from that of ATP-bound form. Thus, it appears that ATP-binding, but not its hydrolysis, is essential for assembly and proteolytic activity of HslVU.

The heat-shock protein HslVU from Escherichia coli is a protein-activated ATPase as well as an ATP-dependent proteinase

HslVU in Escherichia coli a new two-component ATP-dependent protease composed of two heat-shock proteins, the HslU ATPase and the HslV peptidase which is related to proteasome beta-type subunits. Here we show that the reconstituted HslVU enzyme degrades not only certain hydrophobic peptides but also various polypeptides, including insulin B-chain, casein, and carboxymethylated lactalbumin. Maximal proteolytic activity was obtained with a 1:2 molar ratio of HslV (a 250-kDa complex) to HslU (a 450-kDa complex). By itself, HslV could slowly hydrolyze these polypeptides, but its activity was stimulated 20-fold by HslU in the presence of ATP. The ATPase activity of HslU was stimulated up to 50% by the protein substrates, but not by nonhydrolyzed proteins, and this stimulation further increased 2-3-fold in the presence of HslV. Concentrations of insulin B-chain that maximally stimulated the ATPase allowed maximal rates of the B-chain hydrolysis. Furthermore, addition of increasing amounts of ADP or N-ethylmaleimide reduced ATP and protein or peptide hydrolysis in parallel. Thus, HslVU is a protein-activated ATPase as well as an ATP-dependent proteinase, and these processes appear linked. Surprisingly, the protein and peptide substrates do not compete with each other for hydrolysis. Lactacystin strongly inhibits protein degradation, but has little effect on peptide hydrolysis, while the peptide aldehydes are potent inhibitors of hydrolysis of small peptides, but have little effect on proteins. Thus, the functional requirements for ATP-dependent hydrolysis of peptides and proteins appear different.

Proteases and their targets in Escherichia coli

Proteolysis in Escherichia coli serves to rid the cell of abnormal and misfolded proteins and to limit the time and amounts of availability of critical regulatory proteins. Most intracellular proteolysis is initiated by energy-dependent proteases, including Lon, ClpXP, and HflB; HflB is the only essential E. coli protease. The ATPase domains of these proteases mediate substrate recognition. Recognition elements in target are not well defined, but are probably not specific amino acid sequences. Naturally unstable protein substrates include the regulatory sigma factors for heat shock and stationary phase gene expression, sigma 32 and RpoS. Other cellular proteins serve as environmental sensors that modulate the availability of the unstable proteins to the proteases, resulting in rapid changes in sigma factor levels and therefore in gene transcription. Many of the specific proteases found in E. coli are well-conserved in both prokaryotes and eukaryotes, and serve critical functions in developmental systems.