Effect of extra N-terminal residues on the stability and folding of human lysozyme expressed in Pichia pastoris

The molecular modification, expression, and the antibacterial effects studies of human lysozyme

Human lysozyme (hLYZ) has attracted considerable research attention due to its natural and efficient antibacterial abilities and widespread uses. In this study, hLYZ was modified to enhance its enzyme activity and expressed in a Pichia pastoris expression system. A combination mutant HZM(2R-K)-N88D/V110S demonstrated the highest enzyme activity (6213 ± 164 U/mL) in shake flasks, which was 4.07-fold higher when compared with the original strain. Moreover, the recombinant P. pastoris was inducted in a 3 L bioreactor plus methanol/sorbitol co-feeding. After 120 h induction, the antibacterial activity of hLYZ reached 2.23 ± 0.12 × 105 U/mL, with the specific activity increasing to 1.89 × 105 U/mg, which is currently the highest specific activity obtained through recombinant expression of hLYZ. Also, hLYZ supernatants showed 2-fold inhibitory effects toward Staphylococcus aureus and Micrococcus lysodeikticus when compared with HZM(2R-K). Our research generated a hLYZ mutant with high antibacterial capabilities and provided a method for screening of high-quality enzymes.

Site-specific relaxation of peptide bond planarity induced by electrically attracted proton/deuteron observed by neutron crystallography

In structural biology, peptide bonds, fundamental linkages between hundreds of amino acids, of which a protein molecule is composed, have been commonly treated as a plane structure just as Linus Pauling et al. proposed. In this paper, a site-specific peptide bond relaxation mechanism by deuterons whose localization has been suggested by neutron crystallography is proposed. Such deuteron was observed as an arm of neutron scattering length density protruding from the carbonyl oxygen atoms in the main chain in the omit map drawn by neutron crystallography of human lysozyme. Our comprehensive study using x-ray and neutron diffraction and 15 N chemical shifts of individual amide nitrogen atoms within the same peptide bond strongly suggests the relaxation of the electronic resonance structure because of site-specific modulation by protons/deuterons localized on the electron orbital of the carbonyl oxygen. All experimental data used in this examination were obtained at room temperature, which is preferable for enzymatic activity. Such a close interaction between the electron resonance structure of a peptide bond and the exchangeable protons/deuterons well agreed with that observed in an intermediate state in an amide hydrolytic reaction simulated by the ab-initio calculation including water molecules.

Signal Peptide-rheostat Dynamics Delay Secretory Preprotein Folding

Sec secretory proteins are distinguished from cytoplasmic ones by N-terminal signal peptides with multiple roles during post-translational translocation. They contribute to preprotein targeting to the translocase by slowing down folding, binding receptors and triggering secretion. While signal peptides get cleaved after translocation, mature domains traffic further and/or fold into functional states. How signal peptides delay folding temporarily, to keep mature domains translocation-competent, remains unclear. We previously reported that the foldon landscape of the periplasmic prolyl-peptidyl isomerase is altered by its signal peptide and mature domain features. Here, we reveal that the dynamics of signal peptides and mature domains crosstalk. This involves the signal peptide's hydrophobic helical core, the short unstructured connector to the mature domain and the flexible rheostat at the mature domain N-terminus. Through this cis mechanism the signal peptide delays the formation of early initial foldons thus altering their hierarchy and delaying mature domain folding. We propose that sequence elements outside a protein's native core exploit their structural dynamics to influence the folding landscape.

Aspergillus oryzae Rutinosidase: Biochemical and Structural Investigation

The rutinosidase (Rut)-encoding gene Aorut has been expressed in Pichia pastoris with its native signal sequence from Aspergillus oryzae Biochemical and structural investigation of the purified recombinant mature A. oryzae Rut (AoRut), designated rAoRutM, was performed in this study. A 1.7-Å resolution crystal structure of rAoRutM was determined, which is an essential step forward in the utilization of AoRut as a potential catalyst. The crystal structure of rAoRutM was represented by a (β/α)₈ TIM barrel fold with structural similarity to that of rutinosidase from Aspergillus niger (AnRut) and an exo-β-(1,3)-glucanase from Candida albicans The crystal structure revealed that the catalytic site was located in a deep cleft, similarly to AnRut, and that internal cavities and water molecules were also present. Purified rAoRutM hydrolyzed not only 7-O-linked and 3-O-linked flavonoid rutinosides but also 7-O-linked and 3-O-linked flavonoid glucosides. rAoRutM displayed high catalytic activity toward quercetin 3-O-linked substrates such as rutin and isoquercitrin, rather than to the 7-O-linked substrate, quercetin-7-O-glucoside. Unexpectedly, purified rAoRutM exhibited increased thermostability after treatment with endo-β-N-acetylglucosaminidase H. Circular dichroism (CD) spectra of purified intact rAoRutM and of the enzyme after N-deglycosylation showed a typical α-helical CD profile; however, the molar ellipticity values of the peaks at 208 nm and 212 nm differed. The K_m and k _cat values for the substrates modified by rutinose were higher than those for the substrates modified by β-d-glucose.IMPORTANCE Flavonoid glycosides constitute a class of secondary metabolites widely distributed in nature. These compounds are involved in bitter taste or clouding in plant-based foods or beverages, respectively. Flavonoid glycoside degradation can proceed through two alternative enzymatic pathways: one that is mediated by monoglycosidases and another that is catalyzed by a diglycosidase. The present report on the biochemical and structural investigation of A. oryzae rutinosidase provides a potential biocatalyst for industrial applications of flavonoids.

The effects of mutation and modification on the structure and stability of human lysozyme: A molecular link between carbamylation and atherosclerosis

Amino acid mutations in some proteins such as lysozyme lead to genetically disorder variants and adverse pathogenic consequences. Recently, amino acid modifications were known as a risk factor in many related diseases such as uremia and atherosclerosis, showing the importance of these surface-structure changes. Although the structural consequences of the hereditary proteins have been examined extensively, such effects for the protein modifications are known to a lesser extent. One drawback in the examination of protein modifications is hardness in experimental detection of modifications by techniques such as NMR and crystallography. Molecular modeling and simulation can help to understand such phenomena at the molecular levels. It is more rational that the effects of both mutation and modification can be compared in a single protein model. Here, molecular dynamics simulation is used to compare the effects of a disease-related carbamylation modification and an amyloidogenic mutation (D67H) in human lysozyme as a model protein. The results show that the carbamylation adversely effects on the tertiary structure, leading to the similar unfolding pathway to the hereditary amyloidogenic form. The carbamylation leads to the instability of the overall protein conformation, especially on the β-domain, which is a characteristic of hereditary amyloidosis in human lysozymes. The aggregation behaviors of both modified and mutant lysozyme were examined by molecular docking calculations. The results showed that the partially unfolded lysozyme might form tight protein aggregates upon carbamylation similar to the amyloidogenic variant. Both single and all-residues carbamylations impose serious conformational changes to the tertiary structure of lysozyme. It was obtained that carbamylation of lysozyme strongly effects on the stability of N-terminal β-sheet, which can produce a highly unstable conformation. The results of this study not only show the adverse structural consequences of a disease-associated post-translational modification, but it also may be very helpful to understand the molecular basis for many carbamylation-related diseases such as atherosclerosis in ESRD patients. The results show that non-native post-translational modifications may be as structurally important as hereditary mutations.

Tissue-Specificity of Dystrophin-Actin Interactions: Isoform-Specific Thermodynamic Stability and Actin-Binding Function of Tandem Calponin-Homology Domains

Genetic mutations in Duchenne muscular dystrophy (DMD) gene affecting the expression of dystrophin protein lead to a number of muscle disorders collectively called dystrophinopathies. In addition to muscle dystrophin, mutations in brain-specific dystrophin isoforms, in particular those that are expressed in the brain cortex and Purkinje neurons, result in cognitive impairment associated with DMD. These isoforms carry minor variations in the flanking region of the N-terminal actin-binding domain (ABD1) of dystrophin, which is composed of two calponin-homology (CH) domains in tandem. Determining the effect of these sequence variations is critical for understanding the mechanisms that govern varied symptoms of the disease. We studied the impact of differences in the N-terminal flanking region on the structure and function of dystrophin tandem CH domain isoforms. The amino acid changes did not affect the global structure of the protein but drastically affected the thermodynamic stability, with the muscle isoform more stable than the brain and Purkinje isoforms. Actin binding investigated with actin from different sources (skeletal muscle, smooth muscle, cardiac muscle, and platelets) revealed that the muscle isoform binds to filamentous actin (F-actin) with a lower affinity compared to the brain and Purkinje isoforms, and a similar trend was observed with actin from different sources. In addition, all isoforms showed a higher affinity to smooth muscle actin in comparison to actin from other sources. In conclusion, tandem CH domain isoforms might be using minor sequence variations in the N-terminal flanking regions to modulate their thermodynamic stability and actin-binding function, thus leading to specificity in dystrophin-actin interactions in various tissues.

Differential Regulation of Innate and Learned Behavior by Creb1/Crh-1 in Caenorhabditis elegans

Memory formation is crucial for the survival of animals. Here, we study the effect of different crh-1 [Caenorhabditis elegans homolog of mammalian cAMP response element binding protein 1 (CREB1)] isoforms on the ability of C. elegans to form long-term memory (LTM). Null mutants in creb1/crh-1 are defective in LTM formation across phyla. We show that a specific isoform of CREB1/CRH-1, CRH-1e, is primarily responsible for memory related functions of the transcription factor in C. elegans. Silencing of CRH-1e-expressing neurons during training for LTM formation abolishes the LTM of the animal. Further, CRH-1e expression in RIM neurons is sufficient to rescue LTM defects of creb1/crh-1-null mutants. We go on to show that apart from being LTM defective, creb1/crh-1-null animals show defects in innate chemotaxis behavior. We further characterize the amino acids K247 and K266 as responsible for the LTM related functions of CREB1/CRH-1 while being dispensable for its innate chemotaxis behavior. These findings provide insight into the spatial and temporal workings of a crucial transcription factor that can be further exploited to find CREB1 targets involved in the process of memory formation.

SIGNIFICANCE STATEMENT This study elucidates the role of a specific isoform of CREB1/CRH-1, CRH-1e, in Caenorhabditis elegans memory formation and chemosensation. Removal of this single isoform of creb1/crh-1 shows defects in long-term memory formation in the animal and expression of CREB1/CRH-1e in a single pair of neurons is sufficient to rescue the memory defects seen in the mutant animals. We further show that two specific amino acids of CRH-1 are required for the process of memory formation in the animal.

Yeast Surface Display of Antheraea pernyi Lysozyme Revealed α-Helical Antibacterial Peptides in Its N-Terminal Domain

The present study investigated a novel lysozyme ApLyz from the Chinese oak silkmoth, Antheraea pernyi, for its active expression with N- or C-terminus fused to the yeast cell surface, and the antimicrobial activities of the corresponding expressed lysozymes were evaluated. The bactericidal activity of C-terminal fusion of ApLyz surpassed that of the N-terminal fusion, which revealed the implication of an N-terminal stretch of ApLyz in the bactericidal function based on the structural mobility of this region. Two N-terminal peptides of ApLyz (residues 1-15 and 1-32), which primarily consist of amphiphilic α-helices, exerted similar bactericidal efficacy and had a strong preference for the Gram-negative strains. Further investigation revealed that the N-terminal peptides are membrane-targeting peptides causing cell permeabilization and also possess nonmembrane disturbing bactericidal mechanism. Overall, in addition to the key findings of novel bactericidal peptides from silkmoth lysozyme, this work laid the foundation for future improvement of ApLyz by protein engineering.

Transposon for protein engineering

Protein insertional fusion and circular permutation are 2 promising protein engineering techniques for creating integrated functionalities and sequence diversity of a protein, respectively. Finding insertion locations for protein insertional fusion and new termini for circular permutation through a rational approach is not always straightforward, especially, for proteins without detailed structural knowledge. On the contrary, a combinatorial approach facilitates a comprehensive search to evaluate all potential insertion sites and new termini locations. Conventional methods used to create random insertional fusion libraries generate sub-optimal inter-domain linker length and composition between fused proteins. There are also methods available for construction of random circular permutation libraries. However, these methods too, impose many drawbacks, such as significant sequence modification at the new termini of circular permutants and additionally, require re-design of transposons for tailored expression of circular permutants. Furthermore, these conventional methods employ relatively inefficient blunt-end ligation during library construction. In this commentary, we present a concise overview and key findings of engineered Mu transposons, which have recently been developed in our group as a facile and efficient tool to alleviate limitations realized from conventional methods and to construct high quality libraries for random insertional fusion and random circular permutation.

Molecular dynamics study of naturally existing cavity couplings in proteins

Couplings between protein sub-structures are a common property of protein dynamics. Some of these couplings are especially interesting since they relate to function and its regulation. In this article we have studied the case of cavity couplings because cavities can host functional sites, allosteric sites, and are the locus of interactions with the cell milieu. We have divided this problem into two parts. In the first part, we have explored the presence of cavity couplings in the natural dynamics of 75 proteins, using 20 ns molecular dynamics simulations. For each of these proteins, we have obtained two trajectories around their native state. After applying a stringent filtering procedure, we found significant cavity correlations in 60% of the proteins. We analyze and discuss the structure origins of these correlations, including neighbourhood, cavity distance, etc. In the second part of our study, we have used longer simulations (≥100 ns) from the MoDEL project, to obtain a broader view of cavity couplings, particularly about their dependence on time. Using moving window computations we explored the fluctuations of cavity couplings along time, finding that these couplings could fluctuate substantially during the trajectory, reaching in several cases correlations above 0.25/0.5. In summary, we describe the structural origin and the variations with time of cavity couplings. We complete our work with a brief discussion of the biological implications of these results.

Simple and efficient expression of Agaricus meleagris pyranose dehydrogenase in Pichia pastoris

Pyranose dehydrogenase (PDH) is a fungal flavin-dependent sugar oxidoreductase that is highly interesting for applications in organic synthesis or electrochemistry. The low expression levels of the filamentous fungus Agaricus meleagris as well as the demand for engineered PDH make heterologous expression necessary. Recently, Aspergillus species were described to efficiently secrete recombinant PDH. Here, we evaluate recombinant protein production with expression hosts more suitable for genetic engineering. Expression in Escherichia coli resulted in no soluble or active PDH. Heterologous expression in the methylotrophic yeast Pichia pastoris was investigated using two different signal sequences as well as a codon-optimized sequence. A 96-well plate activity screening for transformants of all constructs was established and the best expressing clone was used for large-scale production in 50-L scale, which gave a volumetric yield of 223 mg L⁻¹ PDH or 1,330 U L⁻¹ d⁻¹ in space–time yield. Purification yielded 13.4 g of pure enzyme representing 95.8% of the initial activity. The hyperglycosylated recombinant enzyme had a 20% lower specific activity than the native enzyme; however, the kinetic properties were essentially identical. This study demonstrates the successful expression of PDH in the eukaryotic host organism P. pastoris paving the way for protein engineering. Additionally, the feasibility of large-scale production of the enzyme with this expression system together with a simplified purification scheme for easy high-yield purification is shown.

Terminal amino acids disturb xylanase thermostability and activity

Protein structure is composed of regular secondary structural elements (α-helix and β-strand) and non-regular region. Unlike the helix and strand, the non-regular region consists of an amino acid defined as a disordered residue (DR). When compared with the effect of the helix and strand, the effect of the DR on enzyme structure and function is elusive. An Aspergillus niger GH10 xylanase (Xyn) was selected as a model molecule of (β/α)(8) because the general structure consists of ~10% enzymes. The Xyn has five N-terminal DRs and one C-terminal DR, respectively, which were deleted to construct three mutants, XynΔN, XynΔC, and XynΔNC. Each mutant was ~2-, 3-, or 4-fold more thermostable and 7-, 4-, or 4-fold more active than the Xyn. The N-terminal deletion decreased the xylanase temperature optimum for activity (T(opt)) 6 °C, but the C-terminal deletion increased its T(opt) 6 °C. The N- and C-terminal deletions had opposing effects on the enzyme T(opt) but had additive effects on its thermostability. The five N-terminal DR deletions had more effect on the enzyme kinetics but less effect on its thermo property than the one C-terminal DR deletion. CD data showed that the terminal DR deletions increased regular secondary structural contents, and hence, led to slow decreased Gibbs free energy changes (ΔG(0)) in the thermal denaturation process, which ultimately enhanced enzyme thermostabilities.

Functional expression of recombinant anti-BNP scFv in methylotrophic yeast Pichia pastoris and application as a recognition molecule in electrochemical sensors

Recent studies have revealed the potential of B-type natriuretic peptide (BNP) as a good prognostic marker for patients with heart failure. Antibodies against BNP are expected to be usefully employed in the diagnosis of heart failures. We established a more efficient method to produce functional anti-BNP, single chain variable fragment (scFv) using a eukaryotic expression system of Pichia pastoris. Although analysis of the N-terminal (NT) sequence of the expressed anti-BNP scFv indicated that the two Ste13 sites of the secreted anti-BNP scFv were not cleaved, the specificity of anti-BNP scFv was not affected significantly. The binding activity of anti-BNP scFv against other antigens, against four other antigens, NT probrain peptide (NT-pro BNP), atrial natriuretic peptide (ANP), carcinoembryonic antigen (CEA) and human serum albumin (HSA), was only one thousandth that of the original BNP antigen, which clearly demonstrated the specific binding of recombinant scFv toward BNP. The anti-BNP, scFv-based, electrochemical immunoassay exhibited excellent analytical performance with a detection limit of 1 fg/ml and a wide linear detection range from 1 to 10,000 fg/ml. The optimum culture conditions to obtain the maximum concentration of recombinant scFv were a pH range of 5.0-7.0 and an incubation temperature of 20°C. This anti-BNP scFv expressed in P. pastoris has the potential for promising applications in the diagnosis of heart failure.

Unfolding pathways of goat alpha-lactalbumin as revealed in multiple alignment of molecular dynamics trajectories

Molecular dynamics simulations of protein unfolding were performed at an elevated temperature for the authentic and recombinant forms of goat alpha-lactalbumin. Despite very similar three-dimensional structures, the two forms have significantly different unfolding rates due to an extra N-terminal methionine in the recombinant protein. To identify subtle differences between the two forms in the highly stochastic kinetics of unfolding, we classified the unfolding trajectories using the multiple alignment method based on the analogy between the biological sequences and the molecular dynamics trajectories. A dendrogram derived from the multiple trajectory alignment revealed a clear difference in the unfolding pathways of the authentic and recombinant proteins, i.e. the former reached the transition state in an all-or-none manner while the latter unfolded less cooperatively. It was also found in the classification that the two forms of the protein shared a common transition state structure, which was in excellent agreement with the transition state structure observed experimentally in the Phi-value analysis.

Rational design of affinity peptide ligand by flexible docking simulation

Rational design of affinity peptide ligands of proteins by flexible docking simulation is performed using the SYBYL program package. This approach involves the use of experimental data to verify a scoring function that can be used to assess the affinity of a peptide for its target protein. The enzyme-linked immunosorbent assay (ELISA) data of several peptides displayed on phage surfaces for insulin and lysozyme, respectively, reported in literature are used for the purpose. It is found that the absolute values of the Dscore calculated from the docking correspond well to the ELISA data that relate to the affinity between the peptides and the target molecule. So, the Dscore function is used to assess the affinity of docked peptides in a pentapeptide library designed on the basis of protein (alpha-amylase) structure. As a result, a pentapeptide with a high Dscore value is selected and a hexapeptide (FHENWS) is built by linking serine to its C-terminal to lengthen the peptide. Molecular surface analysis with the MOLCAD program reveals that electrostatic interactions (including hydrogen bonds) and Van der Waals forces contribute to the affinity of the hexapeptide for alpha-amylase. Chromatographic experiments with the immobilized peptide have given further evidence for this observation. Adsorption isotherm described by the Langmuir equation indicates that the apparent binding constant of alpha-amylase to the immobilized hexapeptide was 2.5x10(5)L/mol. Finally, high affinity and specificity of the affinity adsorbent is exemplified by the purification of alpha-amylase from crude fermentation broth of Bacillus subtilis.

Developments in biotechnological production of sweet proteins

Most proteins are tasteless and flavorless, while some proteins elicit a sweet-taste response on the human palate. Six proteins, thaumatin, monellin, mabinlin, brazzein, egg lysozyme, and neoculin (previously considered as curculin) have been identified as sweet-tasting proteins. However, no common features among them have been observed. Herein, recent advances in the research of sweet-tasting proteins and the production of such proteins by biotechnological approaches are reviewed. Information on the structure-sweetness relationship for these proteins would help not only in the clarification of the mechanism of interaction of sweet-tasting proteins with their receptors, but also in the design of more effective low-calorie sweeteners.

Impact of the native-state stability of human lysozyme variants on protein secretion by Pichia pastoris

We report the secreted expression by Pichia pastoris of two human lysozyme variants F57I and W64R, associated with systemic amyloid disease, and describe their characterization by biophysical methods. Both variants have a substantially decreased thermostability compared with wild-type human lysozyme, a finding that suggests an explanation for their increased propensity to form fibrillar aggregates and generate disease. The secreted yields of the F57I and W64R variants from P. pastoris are 200- and 30-fold lower, respectively, than that of wild-type human lysozyme. More comprehensive analysis of the secretion levels of 10 lysozyme variants shows that the low yields of these secreted proteins, under controlled conditions, can be directly correlated with a reduction in the thermostability of their native states. Analysis of mRNA levels in this selection of variants suggests that the lower levels of secretion are due to post-transcriptional processes, and that the reduction in secreted protein is a result of degradation of partially folded or misfolded protein via the yeast quality control system. Importantly, our results show that the human disease-associated mutations do not have levels of expression that are out of line with destabilizing mutations at other sites. These findings indicate that a complex interplay between reduced native-state stability, lower secretion levels, and protein aggregation propensity influences the types of mutation that give rise to familial forms of amyloid disease.

Expression of an anti-CD33 single-chain antibody by Pichia pastoris

CD33 is a cell surface glycoprotein expressed on cells of myelomonocytic lineage, leukaemic cells, but not haematopoietic stem cells. By virtue of its expression pattern, CD33 has become a popular target for new immunotherapeutic approaches to treat acute myeloid leukaemia. The methylotrophic yeast Pichia pastoris strain KM71H was used to produce an anti-CD33 single chain variable fragment (scFv), with the intention of conjugation to a radioisotope, for therapeutic use. To direct secreted expression of the anti-CD33-scFv the alpha-mating factor secretory signal sequence (alpha-MF) was used, with constructs containing a complete (CS) and incomplete (INCS) cleavage site to accommodate the potential outcomes of dibasic endopeptidase, Kex2, and dipeptidyl amino peptidase, Ste13, processing. The anti-CD33-scFv was expressed in BMMY cultures using both constructs, with a final yield of 48 mg/l (CS) and 11 mg/l (INCS). N-terminal sequencing showed that the CS-scFv had not been cleaved by Ste13, leaving amino acids EAEA at the N-terminus. The INCS-scFv construct produced a mixture of 50% authentic scFv and 50% with 11 amino acids from the alpha-MF remaining at the N-terminus. Despite the aberrations in alpha-MF processing, the anti-CD33-scFv's produced from both constructs were found to be functional. Flow cytometry and Biacore analysis demonstrated binding to target antigen CD33 on the surface of human leukaemic cell line HL-60, and to recombinant soluble CD33 respectively.

High yield secretion of the sweet-tasting protein lysozyme from the yeast Pichia pastoris

Hen egg lysozyme (HEL) is one of the sweet-tasting proteins. To understand why lysozyme is sweet, the enzyme was synthesized at high yields by a recombinant method. The mature HEL gene was cloned from a Taq polymerase-amplified PCR product into the Pichia pastoris expression and secretion vector pPIC6alpha. This expression vector contains both the Saccharomyces cerevisiae pre-pro alpha-mating factor secretion signal and the blasticidin resistance gene (bsd) for selection of transformants in bacteria and yeast. Expression of HEL was carried out in fermenter cultures. Culture supernatants were concentrated by ultrafiltration and purified by CM-ion exchange chromatography. Approximately 400 mgL-1 of recombinant HEL was obtained. The high yield of recombinant lysozyme enabled us to perform a sensory analysis in humans. The purified recombinant lysozyme elicited as a sweet taste sensation as does the lysozyme purified directly from egg white, and showed full lytic activity against cells of Micrococcus luteus. These results demonstrate that the P. pastoris expression system with the blasticidin S selection system is useful in producing recombinant sweet-tasting protein in active form at a high yield.

Determination of the complete cDNA sequence, construction of expression systems, and elucidation of fibrinolytic activity for Tapes japonica lysozyme

The lysozyme of the marine bivalve, Tapes japonica (13.8 kDa), belongs to the invertebrate lysozyme family and displays both chitinase and isopeptidase activities. We determined the complete cDNA sequence and constructed effective expression systems for this enzyme using Escherichia coli (BL21) and Pichia pastoris. The native and recombinant proteins indicated lysozyme activity and isopeptidase activity, including the proteolysis of d-dimer, a plasminolytic product of stabilized polymeric fibrin. These results will be utilized for the structural and functional study of invertebrate lysozymes, and for the development of applications for thrombosis therapies.

Secretion of Pem-CMG, a peptide in the CHH/MIH/GIH family of Penaeus monodon, in Pichia pastoris is directed by secretion signal of the alpha-mating factor from Saccharomyces cerevisiae

The CHH/MIH/GIH peptide family of black tiger prawn (Paneaus monodon) is important in shrimp reproduction and growth enhancement. In this study, the cDNA that encodes the complete peptide that is related to the CHH/MIH/GIH family (so-called, Pem-CMG) in the eyestalk of P. monodon was successfully expressed in a methylotrophic yeast Pichia pastoris under the control of an alcohol oxidase promoter. In order to obtain the secreted Pem-CMG, a secretion signal of either the Saccharomyces cerevisiae alpha-factor or Pem-CMG was employed. The results demonstrated that alphaPem-CMG, either with (alpha2EACMG) or without (alphaCMG) the Glu-Ala repeats, was secreted into the medium, while Pem-CMG with its own secretion signal failed to be secreted. The total protein amount that was secreted from the transformant that contained either alpha2EACMG or alphaMG was approximately 60 mg/l and 150 mg/l, respectively. The N-terminus of the Pem-CMG peptide of both alpha2EACMG and alphaCMG was correctly processed. This produced the mature Pem-CMG peptide.

Construction of an expression system of insect lysozyme lacking thermal stability: the effect of selection of signal sequence on level of expression in the Pichia pastoris expression system

Expression systems of human and silkworm lysozymes were constructed using the methylotrophic yeast Pichia pastoris as a host. The leader sequence and its prepro peptide of alpha-factor (a peptide pheromone derived from yeast) and the native signal sequences of these lysozymes, were used as secretion signals. When the alpha-factor leader is used as the signal sequence, human lysozyme is secreted at a much higher level than is silkworm lysozyme. On the other hand, silkworm lysozyme, when its native signal is used, is secreted more efficiently than human lysozyme. Therefore, we expected that human lysozyme cDNA with a silkworm native signal would be secreted more efficiently than human lysozyme with its native signal. However, its level of expression was not increased. This result indicates that the native signal of silkworm lysozyme does not promote the secretion of the lysozyme, but rather alpha-factor leader inhibits the secretion. Silkworm lysozyme with the alpha-factor leader is so unstable that it could be easily attacked by some proteases and our findings suggest that the level of expression of heterologous protein with signal peptides and its stability are greatly affected by the selection of the appropriate secretion signal sequence.

Secreted production of a custom-designed, highly hydrophilic gelatin in Pichia pastoris

A custom-designed, highly hydrophilic gelatin was produced in Pichia pastoris. Secreted production levels in single-copy transformants were in the range 3-6 g/l of clarified broth and purification to near homogeneity could be accomplished by differential ammonium sulfate precipitation. Despite the fact that gelatins are highly susceptible to proteolysis because of their unfolded structure, the recombinant protein was shown to be fully intact by SDS-PAGE, N-terminal sequencing, gel filtration chromatography and mass spectrometry. Owing to its highly hydrophilic nature, the migration of the synthetic gelatin in SDS-PAGE was severely delayed. Esterification of the carboxylic amino acid side chains resulted in normal migration. The high polarity of the synthetic gelatin also accounts for its negligible surface activity in water at concentrations up to 5% (w/v), as determined by tensiometry. Circular dichroism spectrometry showed that the non-hydroxylated gelatin did not form triple helices at 4 degrees C. The spectrum was even more representative of the random coil conformation than the spectrum of natural non-hydroxylated gelatins.

The stability and folding process of amyloidogenic mutant human lysozymes

Amyloid deposits are frequently formed by mutant proteins that have a lower stability than the wild-type proteins. Some reports, however, have shown that mutant-induced thermodynamic destabilization is not always a general mechanism of amyloid formation. To obtain a better understanding of the mechanism of amyloid fibril formation, we show in this study that equilibrium and kinetic refolding-unfolding reaction experiments with two amyloidogenic mutant human lysozymes (I56T and D67H) yield folding pathways that can be drawn as Gibbs energy diagrams. The equilibrium stabilities between the native and denatured states of both mutant proteins were decreased, but the degrees of instability were different. The Gibbs energy diagrams of the folding process reveal that the Gibbs energy change between the native and folding intermediate states was similar for both proteins, and also that the activation Gibbs energy change from the native state to the transition state decreased. Our results confirm that the tendency to favor the intermediate of denaturation facilitates amyloid formation by the mutant human lysozymes more than equilibrium destabilization between the native and completely denatured states does.