Purification and characterization of human procolipase expressed in yeast cells

Pancreatic lipase-related protein 2 digests fats in human milk and formula in concert with gastric lipase and carboxyl ester lipase

BACKGROUND

Dietary fats must be digested into fatty acids and monoacylglycerols prior to absorption. In adults, colipase-dependent pancreatic triglyceride lipase (PTL) contributes significantly to fat digestion. In newborn rodents and humans, the pancreas expresses low levels of PTL. In rodents, a homologue of PTL, pancreatic lipase-related protein 2 (PLRP2), and carboxyl ester lipase (CEL) compensate for the lack of PTL. In human newborns, the role of PLRP2 in dietary fat digestion is unclear. To clarify the potential of human PLRP2 to influence dietary fat digestion in newborns, we determined PLRP2 activity against human milk and infant formula.

METHODS

The activity of purified recombinant PLRP2, gastric lipase (GL), and CEL against fats in human milk and formula was measured with each lipase alone and in combination with a standard pH-stat assay.

RESULTS

Colipase added to human milk stimulated fat digestion. PLRP2 and CEL had activity against human milk and formula. Predigestion with GL increased PLRP2 activity against both substrates. Together, CEL and PLRP2 activity was additive with formula and synergistic with human milk.

CONCLUSION

PLRP2 can digest fats in human milk and formula. PLRP2 acts in concert with CEL and GL to digest fats in human milk in vitro.

Porcine pancreatic lipase related protein 2 has high triglyceride lipase activity in the absence of colipase

Efficient dietary fat digestion is essential for newborns who consume more dietary fat per body weight than at any other time of life. In many mammalian newborns, pancreatic lipase related protein 2 (PLRP2) is the predominant duodenal lipase. Pigs may be an exception since PLRP2 expression has been documented in the intestine but not in the pancreas. Because of the differences in tissue-specific expression, we hypothesized that the kinetic properties of porcine PLRP2 would differ from those of other mammals. To characterize its properties, recombinant porcine PLRP2 was expressed in HEK293T cells and purified to homogeneity. Porcine PLRP2 had activity against tributyrin, trioctanoin and triolein. The activity was not inhibited by bile salts and colipase, which is required for the activity of pancreatic triglyceride lipase (PTL), minimally stimulated PLRP2 activity. Similar to PLRP2 from other species, PLRP2 from pigs had activity against galactolipids and phospholipids. Importantly, porcine PLRP2 hydrolyzed a variety of dietary substrates including pasteurized human mother's milk and infant formula and its activity was comparable to that of PTL. In conclusion, porcine PLRP2 has broad substrate specificity and has high triglyceride lipase activity even in the absence of colipase. The data suggest that porcine PLRP2 would be a suitable lipase for inclusion in recombinant preparations for pancreatic enzyme replacement therapy.

Identification of amino acids in human colipase that mediate adsorption to lipid emulsions and mixed micelles

The adsorption of colipase is essential for pancreatic triglyceride lipase activity and efficient dietary fat digestion. Yet, little is known about which specific amino acids in the hydrophobic surface of colipase influence adsorption. In this study, we systematically substituted alanine or tryptophan at residues implicated in adsorption of colipase to an interface. We expressed, purified recombinant colipase mutants and characterized the ability of each alanine mutant to restore activity to lipase in the presence of bile salts. The functions of L16A, Y55A, I79A and F84A colipase were most impaired with activities ranging from 20 to 60% of wild-type colipase. We next characterized the fluorescence properties of the tryptophan mutants in the absence and presence of bile-salt-oleic acid mixed micelles. We performed steady-state emission spectra to determine peak shift and I330/I350 ratio and acrylamide quenching curves to characterize the environment of the residues. The analysis supports a model of adsorption that includes residues Leu 34 and Leu 36 on the 2nd loop, Tyr 55 and Tyr 59 on the 3rd loop and Ile 75 and Ile 79 on the 4th loop. The analysis confirms that Phe 84 is not part of the adsorption surface and likely stabilizes the conformation of colipase. Contrary to the predictions of computer modeling, the results provide strong support for an essential role of Tyr 55 in colipase adsorption to mixed micelles. The results indicate that the adsorption of colipase to mixed micelles is mediated by specific residues residing in a defined surface of colipase.

Improved secretion of Candida antarctica lipase B with its native signal peptide in Pichia pastoris

Secretion efficiency of the 85-amino acid Sacchromyces cerevisiae alpha signal peptide and the 25-amino acid Candida antarctica lipase B signal (nsB) peptide were compared. Three reporter proteins used for the study are C. antarctica lipase A (CalA), lipase B (CalB) and hGMCSF. The copy number of recombinant α-CalB and nsB-CalB clones was determined by qPCR and clones with equivalent gene copies were used for comparative analysis. About threefold increased CalB production corresponding to an activity of 480 U ml(-1) was obtained with its native signal peptide, whereas with the alpha signal peptide the maximum activity was 160 U ml(-1). Also, CalB was secreted as a mature protein with native N-terminus when fused to its own signal peptide, while unprocessed CalB with N-terminal extension was detected with the alpha signal peptide. Real time PCR analysis of CalB strains indicated that the difference in protein expression was not at the transcriptional level. The nsB signal sequence was also effective in secreting CalA enzyme and its secretion efficiency was on par with the alpha signal sequence. Further, hGMCSF fused inframe with the nsB signal peptide was also efficiently secreted into the medium. These results indicate that the nsB signal peptide can be a better alternative to alpha signal peptide for heterologous protein expression in Pichia pastoris.

The Arg92Cys colipase polymorphism impairs function and secretion by increasing protein misfolding

Colipase is essential for efficient fat digestion. An arginine-to-cysteine polymorphism at position 92 of colipase (Arg92Cys) associates with an increased risk for developing type-2 diabetes through an undefined mechanism. To test our hypothesis that the extra cysteine increases colipase misfolding, thereby altering its intracellular trafficking and function, we expressed Cys92 colipase in HEK293T cells. Less Cys92 colipase is secreted and more is retained intracellularly in an insoluble form compared with Arg92 colipase. Nonreducing gel electrophoresis suggests the folding of secreted Cys92 colipase differs from Arg92 colipase. Cys92 colipase misfolding does not trigger the unfolded protein response (UPR) or endoplasmic reticulum (ER) stress. The ability of secreted Cys92 colipase to stimulate pancreatic triglyceride lipase (PTL) is reduced with all substrates tested, particularly long-chain triglycerides. The reaction of Cys92 colipase with triolein and Intralipid has a much longer lag time, reflecting decreased ability to anchor PTL on those substrates. Our data predicts that humans with the Arg92Cys substitution will secrete less functional colipase into the duodenum and have less efficient fat digestion. Whether inefficient fat digestion or another property of colipase contributes to the risk for developing diabetes remains to be clarified.

Beyond de-foaming: the effects of antifoams on bioprocess productivity

Antifoams are often added to bioprocesses with little knowledge of their impact on the cells or product. However, it is known that certain antifoams can affect the growth rates of both prokaryotic and eukaryotic organisms in addition to changing surface properties such as lipid content, resulting in changes to permeability. This in turn can be beneficial to a recombinant protein production system for soluble proteins, as has been demonstrated by increased secretion of α-amylase and GFP, or achievement of greater yields of protein due to increased biomass. However, in some cases, certain concentrations of antifoams appear to have a detrimental effect upon cells and protein production, and the effects vary depending upon the protein being expressed. These findings emphasise the importance of optimising and understanding antifoam addition to bioprocesses.

Kinetic properties of mouse pancreatic lipase-related protein-2 suggest the mouse may not model human fat digestion

Genetically engineered mice have been employed to understand the role of lipases in dietary fat digestion with the expectation that the results can be extrapolated to humans. However, little is known about the properties of mouse pancreatic triglyceride lipase (mPTL) and pancreatic lipase-related protein-2 (mPLRP2). In this study, both lipases were expressed in Pichia Pastoris GS115, purified to near homogeneity, and their properties were characterized. Mouse PTL displayed the kinetics typical of PTL from other species. Like mPTL, mPLRP2 exhibited strong activity against various triglycerides. In contrast to mPTL, mPLRP2 was not inhibited by increasing bile salt concentration. Colipase stimulated mPLRP2 activity 2- to 4-fold. Additionally, mPTL absolutely required colipase for absorption to a lipid interface, whereas mPLRP2 absorbed fully without colipase. mPLRP2 had full activity in the presence of BSA, whereas BSA completely inhibited mPTL unless colipase was present. All of these properties of mPLRP2 differ from the properties of human PLRP2 (hPLRP2). Furthermore, mPLRP2 appears capable of compensating for mPTL deficiency. These findings suggest that the molecular mechanisms of dietary fat digestion may be different in humans and mice. Thus, extrapolation of dietary fat digestion in mice to humans should be done with care.

Pharmacology and safety of glycerol phenylbutyrate in healthy adults and adults with cirrhosis

Phenylbutyric acid (PBA), which is approved for treatment of urea cycle disorders (UCDs) as sodium phenylbutyrate (NaPBA), mediates waste nitrogen excretion via combination of PBA-derived phenylacetic acid with glutamine to form phenylactylglutamine (PAGN) that is excreted in urine. Glycerol phenylbutyrate (GPB), a liquid triglyceride pro-drug of PBA, containing no sodium and having favorable palatability, is being studied for treatment of hepatic encephalopathy (HE). In vitro and clinical studies have been performed to assess GPB digestion, safety, and pharmacology in healthy adults and individuals with cirrhosis. GPB hydrolysis was measured in vitro by way of pH titration. Twenty-four healthy adults underwent single-dose administration of GPB and NaPBA and eight healthy adults and 24 cirrhotic subjects underwent single-day and multiple-day dosing of GPB, with metabolites measured in blood and urine. Simulations were performed to assess GPB dosing at higher levels. GPB was hydrolyzed by human pancreatic triglyceride lipase, pancreatic lipase-related protein 2, and carboxyl-ester lipase. Clinical safety was satisfactory. Compared with NaPBA, peak metabolite blood levels with GPB occurred later and were lower; urinary PAGN excretion was similar but took longer. Steady state was achieved within 4 days for both NaPBA and GPB; intact GPB was not detected in blood or urine. Cirrhotic subjects converted GPB to PAGN similarly to healthy adults. Simulations suggest that GPB can be administered safely to cirrhotic subjects at levels equivalent to the highest approved NaPBA dose for UCDs.

CONCLUSION

GPB exhibits delayed release characteristics, presumably reflecting gradual PBA release by pancreatic lipases, and is well tolerated in adults with cirrhosis, suggesting that further clinical testing for HE is warranted.

Physiological parameters governing the action of pancreatic lipase

The most widely used pharmacological therapies for obesity and weight management are based on inhibition of gastrointestinal lipases, resulting in a reduced energy yield of ingested foods by reducing dietary lipid absorption. Colipase-dependent pancreatic lipase is believed to be the major gastrointestinal enzyme involved in catalysis of lipid ester bonds. There is scant literature on the action of pancreatic lipase under the range of physiological conditions that occur within the human small intestine, and the literature that does exist is often contradictory. Due to the importance of pancreatic lipase activity to nutrition and weight management, the present review aims to assess the current body of knowledge with regards to the physiology behind the action of this unique gastrointestinal enzyme system. Existing data would suggest that pancreatic lipase activity is affected by intestinal pH, the presence of colipase and bile salts, but not by the physiological range of Ca ion concentration (as is commonly assumed). The control of secretion of pancreatic lipase and its associated factors appears to be driven by gastrointestinal luminal content, particularly the presence of acid or digested proteins and fats in the duodenal lumen. Secretion of colipase, bile acids and pancreatic lipase is driven by cholecystokinin and secretin release.

Trp-107 and trp-253 account for the increased steady state fluorescence that accompanies the conformational change in human pancreatic triglyceride lipase induced by tetrahydrolipstatin and bile salt

The conformation of a surface loop, the lid, controls activity of pancreatic triglyceride lipase (PTL) by moving from a position that sterically hinders substrate access to the active site into a new conformation that opens and configures the active site. Movement of the lid is accompanied by a large change in steady state tryptophan fluorescence. Although a change in the microenvironment of Trp-253, a lid residue, could account for the increased fluorescence, the mechanism and tryptophan residues have not been identified. To identify the tryptophan residues responsible for the increased fluorescence and to gain insight into the mechanism of lid opening and the structure of PTL in aqueous solution, we examined the effects of mutating individual tryptophan residues to tyrosine, alanine, or phenylalanine on lipase activity and steady state fluorescence. Substitution of tryptophans 86, 107, 253, and 403 reduced activity against tributyrin with the largest effects caused by substituting Trp-86 and Trp-107. Trp-107 and Trp-253 fluorescence accounts for the increased fluorescence emissions of PTL that is stimulated by tetrahydrolipstatin and sodium taurodeoxycholate. The largest contribution is from Trp-107. Contrary to the prediction from the crystal structure of PTL, Trp-107 is likely exposed to solvent. Both tetrahydrolipstatin and sodium taurodeoxycholate are required to produce the increased fluorescence in PTL. Alone, neither is sufficient. Colipase does not significantly influence the conformational changes leading to increased emission fluorescence. Thus, Trp-107 and Trp-253 contribute to the change in steady state fluorescence that is triggered by mixed micelles of inhibitor and bile salt. Furthermore, the results suggest that the conformation of PTL in solution differs significantly from the conformation in crystals.

Cloning, expression and characterization of recombinant elastase from Pseudomonas aeruginosa in Picha pastoris

The gene lasB from Pseudomonas aeruginosa, which encoded elastase, was cloned and firstly successfully expressed in Pichia pastoris stain KM71 under the control of AOX promoter. The effects on the recombinant elastase activities of different pH, different temperatures and different metal ions were assayed. The full-length gene (1497 bp) encodes a preproenzyme including an N-terminal signal peptide (23 aa), a propeptide (197 aa) and mature elastase (301 aa). The recombinant elastase was secreted into culture supernatants using signal sequence from lasB and showed a single band at about 34 kDa by SDS-PAGE. The recombinant elastase expression hit the highest level of approximately 450 mg/L and the specific elastolytic activity of the recombinant elastase was 130 U/ml, which was approximately 26-fold higher than that of elastase obtained from P. aeruginosa. The optimal temperature and pH of the recombinant elastase was 28 degrees C and 7.4, respectively. The enzyme possessed high resistance to heat, and can be activated by Ca(2+). These enzyme properties suggested that it could be produced in an industrial scale and has the potential to be a commercial enzyme.

A polymorphism in the gene encoding procolipase produces a colipase, Arg92Cys, with decreased function against long-chain triglycerides

Type 2 diabetes mellitus is a multifactorial and polygenic disorder with increasing prevalence. Recently, a polymorphism in the gene encoding procolipase, a cysteine for arginine substitution at position 92, was associated with type 2 diabetes in two human populations. Because procolipase plays a critical role in dietary fat metabolism, polymorphisms that affect the function of procolipase could influence the development of type 2 diabetes. We hypothesized that the Arg92Cys polymorphism has functional consequences. To test our hypothesis, we expressed recombinant cysteine 92 (Cys92) procolipase in a yeast expression system and compared the function and stability of purified Cys92 with that of the more common arginine 92 (Arg92) procolipase. Cys92 fully restored the activity of bile-salt inhibited lipase with short- and medium-chain triglycerides but only had 50% of Arg92 function with long-chain triglycerides. After storage at 4 degrees C, Cys92 lost the ability to restore pancreatic triglyceride lipase activity with medium- and long-chain triglycerides. The loss of function correlated with the inability of Cys92 to anchor lipase on an emulsion surface and oxidation of the cysteine. No detectable degradation or intramolecular disulfide formation occurred in Cys92 after storage. Our findings demonstrate that the Arg92Cys polymorphism decreases the function of Cys92 colipase. This change may contribute to the development of type 2 diabetes.

Val-407 and Ile-408 in the beta5'-loop of pancreatic lipase mediate lipase-colipase interactions in the presence of bile salt micelles

In a previous study, we demonstrated that the beta5'-loop in the C-terminal domain of human pancreatic triglyceride lipase (hPTL) makes a major contribution in the function of hPTL (Chahinian et al. (2002) Biochemistry 41, 13725-13735). In the present study, we characterized the contribution of three residues in the beta5'-loop, Val-407, Ile-408, and Leu-412, to the function of hPTL. By substituting charged residues, aspartate or lysine, in these positions, we altered the hydrophilic to lipophilic ratio of the beta5'-loop. Each of the mutants was expressed, purified, and characterized for activity and binding with both monolayers and emulsions and for binding to colipase. Experiments with monolayers and with emulsions suggested that the interaction of hPTL with a phospholipid monolayer differs from the interaction of the hPTL-colipase complex with a dicaprin monolayer or a triglyceride emulsion (i.e. neutral lipids). Val-407, Ile-408, and Leu-412 make major contributions to interactions with monolayers, whereas only Val-407 and Ile-408 appear essential for activity on triglyceride emulsions in the presence of bile salt micelles. In solutions of taurodeoxycholate at micellar concentrations, a major effect of the beta5'-loop mutations is to change the interaction between hPTL and colipase. These observations support a major contribution of residues in the beta5'-loop in the function of hPTL and suggest that a third partner, bile salt micelles or the lipid interface or both, influence the binding of colipase and hPTL through interactions with the beta5'-loop.

Real-time measurement of solute partitioning to lipid monolayers

The interaction of a peripheral protein with a lipid-water interface can show a pronounced dependence on the composition and two-dimensional packing density of the lipids that comprise the interface. We report a novel optical method for measuring the adsorption of macromolecules, such as proteins and nucleic acids, and smaller solutes, such as drugs, to lipid monolayers at the gas-liquid interface. Using fluorescence emission from proteins and a small molecule, we demonstrate that the emissions from these solutes when in the aqueous phase and when associated with the monolayer can be temporally separated. Such separation allows measurement of the extent of solute adsorption, spectral characterization of the adsorbed solute, and characterization of lipid organization using adsorption kinetics. The method does not require, but is compatible with, the solute having different spectral properties in the bulk and surface phases. Indeed, if optical signals from adsorbed and soluble solute are the same or their relationship is known, absolute surface excess of adsorbed solute can be calculated without independent calibration. With appropriate instrumental configuration, the method should be adaptable for screening solutes for interaction with planar monolayers having both well-defined composition and adjustable lipid packing density.

Pancreatic lipase-related protein 2 is the major colipase-dependent pancreatic lipase in suckling mice

Suckling mice express colipase before the expression of pancreatic triglyceride lipase. Yet, efficient fat digestion in newborns requires colipase, suggesting that colipase may act as a cofactor for another lipase such as pancreatic lipase-related protein 2 (PLRP2). We determined whether PLRP2 or another lipase depends on colipase for maximal activity in newborn mice by analyzing extracts from the pancreas of 4-d-old colipase-deficient and PLRP2-deficient mice. Pancreatic extracts from colipase-deficient pups had lipase activity that was stimulated onefold by the addition of exogenous colipase (P<0.001). The activity was completely inhibited by an antibody against pancreatic triglyceride lipase that also recognizes PLRP2. In contrast, pancreatic extracts from PLRP2-deficient pups had significantly lower baseline activity and no colipase-dependent activity. The baseline activity was not inhibited by the anti-pancreatic triglyceride lipase antibody or an antibody against carboxyl ester lipase. We next separated the extracts into two fractions, one containing PLRP2 and the other devoid of PLRP2. All of the colipase-dependent activity segregated with the PLRP2-containing fraction, consistent with the conclusion that PLRP2 is the major colipase-dependent lipase in the pancreas of newborns.

Pancreatic triacylglycerol lipase in a hibernating mammal. II. Cold-adapted function and differential expression

Thirteen-lined ground squirrels (Spermophilus tridecemlineatus) exploit the low-temperature activity of pancreatic triacylglycerol lipase (PTL) during hibernation. Lipolytic activity at body temperatures associated with hibernation was examined using recombinant ground squirrel and human PTLs expressed in yeast. Both the human and ground squirrel enzymes displayed high activity at temperatures as low as 0 degrees C and showed Q10 values of 1.2-1.5 over a range of 37-7 degrees C. These studies indicate that low-temperature lipolysis is a general property of PTL and does not require protein modifications unique to mammalian cells and/or the hibernating state. Western blots show elevated levels of PTL protein during hibernation in both heart and white adipose tissue (WAT). Significant increases in PTL gene expression are seen in heart, WAT, and testes; but not in pancreas, where PTL mRNA levels are highest. Upregulation of PTL in testes is also accompanied by expression of the PTL-specific cofactor, colipase. The multi-tissue expression of PTL during hibernation supports its role as a key enzyme that shows high activity at low temperatures.

Colipase residues Glu64 and Arg65 are essential for normal lipase-mediated fat digestion in the presence of bile salt micelles

Pancreatic triglyceride lipase (PTL) requires colipase for activity. Various constituents in meals and in bile, particularly bile acids, inhibit PTL. Colipase restores activity to lipase in the presence of inhibitory substances like bile acids. Presumably, colipase functions by anchoring and orienting PTL at the oil-water interface. The x-ray structure of the colipase.PTL complex supports this model. In the x-ray structure, colipase has a hydrophobic surface positioned to bind substrate and a hydrophilic surface, lying opposite the hydrophobic surface, with two putative lipase-binding domains, Glu(45)/Asp(89) and Glu(64)/Arg(65). To determine whether the hydrophilic surface interacts with PTL in solution, we introduced mutations into the putative PTL binding domains of human colipase. Each mutant was expressed, purified, and assessed for activity against various substrates. Most of the mutants showed impaired ability to reactivate PTL, with mutations in the Glu(64)/Arg(65) binding site causing the greatest effect. Analysis indicated that the mutations decreased the affinity of the colipase mutants for PTL and prevented the formation of PTL.colipase complexes. The impaired function of the mutants was most apparent when assayed in micellar bile salt solutions. Most mutants stimulated PTL activity normally in monomeric bile salt solutions. We also tested the mutants for their ability to bind substrate and anchor lipase to tributyrin. Even though the ability of the mutants to anchor PTL to an interface decreased in proportion to their activity, each mutant colipase bound to tributyrin to the same extent as wild type colipase. These results demonstrate that the hydrophilic surface of colipase interacts with PTL in solution to form active colipase.PTL complexes, that bile salt micelles influence that binding, and that the proper interaction of colipase with PTL requires the Glu(64)/Arg(65) binding site.

Low-temperature increases the yield of biologically active herring antifreeze protein in Pichia pastoris

Antifreeze proteins and antifreeze glycoproteins are structurally diverse molecules that share a common property in binding to ice crystals and inhibiting ice crystal growth. Type II fish antifreeze protein of Atlantic herring (Clupea harengus harengus) is unique in its requirement of Ca(2+) for antifreeze activity. In this study, we utilized the secretion vector pGAPZalpha A to express recombinant herring antifreeze protein (WT) and a fusion protein with a C-terminal six-histidine tag (WT-6H) in yeast Pichia pastoris wild-type strain X-33 or protease-deficient strain SMD1168H. Both recombinant proteins were secreted into the culture medium and properly folded and functioned as the native herring antifreeze protein. Furthermore, our studies demonstrated that expression at a lower temperature increased the yield of the recombinant protein dramatically, which might be due to the enhanced protein folding pathway, as well as increased cell viability at lower temperature. These data suggested that P. pastoris is a useful system for the production of soluble and biologically active herring antifreeze protein required for structural and functional studies.

Recombinant protein expression in Pichia pastoris

The methylotrophic yeast Pichia pastoris is now one of the standard tools used in molecular biology for the generation of recombinant protein. P. pastoris has demonstrated its most powerful success as a large-scale (fermentation) recombinant protein production tool. What began more than 20 years ago as a program to convert abundant methanol to a protein source for animal feed has been developed into what is today two important biological tools: a model eukaryote used in cell biology research and a recombinant protein production system. To date well over 200 heterologous proteins have been expressed in P. pastoris. Significant advances in the development of new strains and vectors, improved techniques, and the commercial availability of these tools coupled with a better understanding of the biology of Pichia species have led to this microbe's value and power in commercial and research labs alike.

Isolation of a funnel-web spider polypeptide with homology to mamba intestinal toxin 1 and the embryonic head inducer Dickkopf-1

We have isolated and determined the amino acid sequence of a novel peptide component from the venom of the Australian funnel-web spider Hadronyche versuta. This 68-residue toxin, ACTX-Hvf17, does not function like classical neurotoxins in modulating ion channel function as evidenced by its lack of insecticidal activity and its inability to affect vertebrate smooth or skeletal muscle contractility. The peptide shows significant sequence homology with mamba intestinal toxin 1 (MIT1) and to a lesser extent with a variety of colipases. The strong structural homology between MIT1 and porcine colipase leads us to propose that ACTX-Hvf17 also adopts the MIT1/colipase three-dimensional fold. However, we show that ACTX-Hvf17 has no colipase activity and does not stimulate muscle contractility like MITI. We also show that MIT1 and ACTX-Hvf17 display significant sequence homology with the C-terminal cysteine-rich domain of the Dickkopf-1 family of proteins that induce head formation in developing embryos, which leads us to propose that this domain of Dickkopf-1 also adopts the MIT1 colipase fold.

Heterologous protein expression in the methylotrophic yeast Pichia pastoris

During the past 15 years, the methylotrophic yeast Pichia pastoris has developed into a highly successful system for the production of a variety of heterologous proteins. The increasing popularity of this particular expression system can be attributed to several factors, most importantly: (1) the simplicity of techniques needed for the molecular genetic manipulation of P. pastoris and their similarity to those of Saccharomyces cerevisiae, one of the most well-characterized experimental systems in modern biology; (2) the ability of P. pastoris to produce foreign proteins at high levels, either intracellularly or extracellularly; (3) the capability of performing many eukaryotic post-translational modifications, such as glycosylation, disulfide bond formation and proteolytic processing; and (4) the availability of the expression system as a commercially available kit. In this paper, we review the P. pastoris expression system: how it was developed, how it works, and what proteins have been produced. We also describe new promoters and auxotrophic marker/host strain combinations which extend the usefulness of the system.

Human pancreatic triglyceride lipase expressed in yeast cells: purification and characterization

A cDNA clone encoding human pancreatic triglyceride lipase was cloned into a yeast expression vector so that the yeast PHO1 signal peptide replaced the native signal peptide. Pichia pastoris cells were transfected with the vector, and clones expressing human pancreatic triglyceride lipase were isolated. Recombinant human pancreatic lipase was expressed in broth cultures and was purified from the medium by DEAE blue Sepharose and hydroxyapatite chromatography. The highly purified lipase had specific activities for various triglyceride substrates identical to those of tissue-purified human pancreatic triglyceride lipase; it was inhibited by bile salts, required colipase for activity, and demonstrated interfacial activation. This expression system is suitable for the rapid, efficient production of human pancreatic triglyceride lipase in amounts adequate for biophysical studies.