Simple purification method for a recombinantly expressed native His-tag-free aminopeptidase A from Lactobacillus delbrueckii

From bitter to delicious: properties and uses of microbial aminopeptidases

Protein hydrolysates are easily digested and utilized by humans and animals, and are less likely to cause allergies. Protein hydrolysis caused by endopeptidases often leads to the exposure of hydrophobic amino acids at the ends of peptides, which consequently causes bitter taste. Microbial aminopeptidases remove the exposed hydrophobic amino acids at the ends of aminopeptides, which improves taste, allowing for easier production. This processe is attacking significant attention from industry and laboratories. Aminopeptidases selectively hydrolyze peptide bonds from the N-terminal of proteins or peptides to produce free amino acids. Aminopeptidases can be classified into leucine, lysine, methionine and proline aminopeptidases by hydrolyzed N-terminal residues; metallo-, serine- and cysteine- aminopeptidases by the reaction mechanisms; dipeptide and triphoptide enzymes by the released number of amino acid residues at the end of hydrolyzed peptides; or acidic, neutral and basic aminopeptidases by their optimal hydrolysis pH. Commercial aminopeptidases are generally produced by microbial fermentation, and are mainly applied in the debittering of protein hydrolysates, the deep hydrolysis of protein, and the production of condiments, cheese, and bioactive peptides, as well as for disease detection in the medical industry.

In vitro assembly of chimeric virus-like particles composed of a porcine circovirus 2b capsid protein and a B-cell epitope of infectious bursal disease virus

OBJECTIVES

To develop a method for in vitro assembly of recombinant proteins expressed in E. coli into chimeric virus-like particles (cVLPs).

RESULTS

A fusion protein (Bepi-Cap-A) between capsid protein (Cap) of PCV2b and B cell epitope (Bepi) of IBDV was expressed in E. Coli, and purified. For assembling them into cVLPs (Bepi-Cap-VLP), the Bepi-Cap-A was suspended in buffer C [0.03% ("%" stands for "v/v" unless otherwise indicated) polyethylene glycol, 0.4 M Tris, 10 mM β-mercaptoethanol, 5% glycerol, 0.02% (w/v) gellan gum, 0.1 M glycine, 0.03% Tween 80, 500 mM NaCl], and incubated. After centrifugation, the pellet was resuspended in buffer D [50 mM Na₂HPO₄, 50 mM NaH₂PO₄, 0.01% (w/v) gellan gum, 0.05 mM EDTA, 500 mM NaCl, 0.03% Tween 80, pH 6.5], and then dialyzed against dialysis buffer (50 mM Na₂HPO₄, 50 mM NaH₂PO₄, 500 mM NaCl, 0.03% Tween 80, pH 6.5). The procedure resulted in typical and immunogenic Bepi-Cap-VLP.

CONCLUSIONS

The data provide a method which is feasible for in vitro assembly of recombinant proteins into chimeric virus-like particles.

Improving the colloidal and sensory properties of a caseinate hydrolysate using particular exopeptidases

Enzymatic hydrolysis with endopeptidases can be used to modify the colloidal properties of food proteins. In this study, sodium caseinate was hydrolyzed with Sternzym BP 25201, containing a thermolysin-like endopeptidase from Geobacillus stearothermophilus as the only peptidase, to a DH of 2.3 ± 1%. The hydrolysate (pre-hydrolysate) obtained was increased in its foam (+35%) and emulsion stability (+200%) compared to untreated sodium caseinate but showed a bitter taste. This hydrolysate was further treated with the exopeptidases PepN, PepX or PepA, acting on the N-terminus of peptides. Depending on the specificity of the exopeptidase used, changes regarding the hydrolysate properties (hydrophobicity, size), colloidal behavior (emulsions, foams) and taste were observed. No changes regarding the bitterness but further improvements regarding the colloidal stability (foam: +69%, emulsion: +29%) were determined after the application of PepA, which is specific for the hydrophilic amino acids Asp, Glu and Ser. By contrast, treatment with the general aminopeptidase PepN resulted in a non-bitter product, with no significant changes regarding the colloidal properties compared to the pre-hydrolysate (p < 0.05). Similar results to those for PepN (reduced bitterness compared to the pre-hydrolysate, enhanced colloidal stability compared to sodium caseinate) were also obtained using commercial Flavourzyme, which was reduced in its endopeptidase activity (exo-flavourzyme). In conclusion, the modifications obtained with the applied exopeptidases offer a potent tool for researchers and the industry to produce non-bitter protein hydrolysates with increased colloidal properties.

Wheat Gluten Amino Acid Analysis by High-Performance Anion-Exchange Chromatography with Integrated Pulsed Amperometric Detection

The present chapter describes an accurate and user-friendly method for determining amino acid composition of wheat gluten proteins and their gliadin and glutenin fractions. The method consists of hydrolysis of the peptide bonds in 6.0 M hydrochloric acid (HCl) solution at 110 °C for 24 h, followed by evaporation of the acid and separation of the free amino acids by high-performance anion-exchange chromatography with integrated pulsed amperometric detection (HPAEC-IPAD). In contrast to conventional methods, the analysis requires neither pre- or post-column derivatization nor a time-consuming oxidation or derivatization step prior to hydrolysis. Correction factors account for incomplete release of Val and Ile even after hydrolysis for 24 h and for losses of Ser during evaporation. Gradient conditions including an extra eluent allow multiple sequential sample analyses without risk of Glu accumulation on the anion-exchange column which otherwise would result from high Gln levels in gluten proteins.

A natural variant of arylsulfatase from Kluyveromyces lactis shows no formylglycine modification and has no enzyme activity

Kluyveromyces lactis is a common fungal microorganism used for the production of enzyme preparations such as β-galactosidases (native) or chymosin (recombinant). It is generally important that enzyme preparations have no unwanted side activities. In the case of β-galactosidase preparations produced from K. lactis, an unwanted side activity could be the presence of arylsulfatase (EC 3.1.6.1). Due to the action of arylsulfatase, an unpleasant "cowshed-like" off-flavor would occur in the final product. The best choice to avoid this is to use a yeast strain without this activity. Interestingly, we found that certain natural K. lactis strains express arylsulfatases, which only differ in one amino acid at position 139. The result of this difference is that K. lactis DSM 70799 (expressing R139 variant) shows no arylsulfatase activity, unlike K. lactis GG799 (expressing S139 variant). After recombinant production of both variants in Escherichia coli, the R139 variant remains inactive, whereas the S139 variant showed full activity. Mass spectrometric analyses showed that the important posttranslational modification of C56 to formylglycine was not found in the R139 variant. By contrast, the C56 residue of the S139 variant was modified. We further investigated the packing and secondary structure of the arylsulfatase variants using optical spectroscopy, including fluorescence and circular dichroism. We found out that the inactive R139 variant exhibits a different structure regarding folding and packing compared to the active S139 variant. The importance of the amino acid residue 139 was documented further by the construction of 18 more variants, whereof only ten showed activity but always reduced compared to the native S139 variant.