Production of bovine beta-lactoglobulin and hen egg ovalbumin by Trichoderma reesei using precision fermentation technology and testing of their techno-functional properties

The food protein ingredient market is dominated by dairy and egg proteins. Both milk whey and egg proteins are challenging proteins to replace, e.g. with plant proteins, due to the unique structural features of the animal proteins that render them highly functional. Thus, to provide a non-animal source of these important proteins the fungal host Trichoderma reesei was utilized for the biotechnical production of recombinant hen ovalbumin (TrOVA) and bovine beta lactoglobulin (TrBLG). These food proteins were investigated using two different promoter systems to test the concept of effectively expressing them in a fungal host. Both proteins were successfully produced in 24 well plate and bioreactor scale. The production level of TrBLG and TrOVA were 1 g/L and 2 g/L, respectively. Both proteins were further purified and characterized, and their functional properties were tested. TrBLG and TrOVA secondary structures determined by circular dichroism corresponded to the proteins of bovine and hen. The T. reesei produced proteins were found to be N-glycosylated, mostly with Man 5. TrBLG had emulsification properties matching to corresponding bovine protein. TrOVA showed excellent foaming characteristics and heat-induced gelation, although the strength of the gel was somewhat lower than with hen ovalbumin, possibly due to the partial degradation of TrOVA or presence of other host proteins. Biotechnical production of whey and egg proteins using precision fermentation technology offers an innovative way to increase the sustainability of the conventional food industry, without further reliance on animal farming. Industrial relevance: The food protein ingredient market is dominated by dairy (largely whey proteins) and egg proteins. Whey proteins are valuable and versatile food ingredients due to their functional and nutritional quality. They are largely used in meat and milk products, low fat products, bakery, confectionary, infant formulas and sports nutrition. Similarly, egg white protein ovalbumin is a highly functional protein ingredient that facilitates structure formation and high nutritional quality in most food products. Together they comprise 40-70% of the revenue in the animal protein ingredients market. Both whey and egg proteins are extremely challenging proteins to replace, e.g., by plant proteins due to their unique structural features that render them with high functionality. Biotechnical production of whey and egg proteins using precision fermentation technology offers an innovative way to increase the sustainability of the conventional food industry, without further reliance on animal farming.

Identification of novel γ-secretase-associated proteins in detergent-resistant membranes from brain

In Alzheimer disease, oligomeric amyloid β-peptide (Aβ) species lead to synapse loss and neuronal death. γ-Secretase, the transmembrane protease complex that mediates the final catalytic step that liberates Aβ from its precursor protein (APP), has a multitude of substrates, and therapeutics aimed at reducing Aβ production should ideally be specific for APP cleavage. It has been shown that APP can be processed in lipid rafts, and γ-secretase-associated proteins can affect Aβ production. Here, we use a biotinylated inhibitor for affinity purification of γ-secretase and associated proteins and mass spectrometry for identification of the purified proteins, and we identify novel γ-secretase-associated proteins in detergent-resistant membranes from brain. Furthermore, we show by small interfering RNA-mediated knockdown of gene expression that a subset of the γ-secretase-associated proteins, in particular voltage-dependent anion channel 1 (VDAC1) and contactin-associated protein 1 (CNTNAP1), reduced Aβ production (Aβ40 and Aβ42) by around 70%, whereas knockdown of presenilin 1, one of the essential γ-secretase complex components, reduced Aβ production by 50%. Importantly, these proteins had a less pronounced effect on Notch processing. We conclude that VDAC1 and CNTNAP1 associate with γ-secretase in detergent-resistant membranes and affect APP processing and suggest that molecules that interfere with this interaction could be of therapeutic use for Alzheimer disease.

Hydrolysis of the amyloid beta-peptide (A beta) 1-40 between Asp23-Val24 produces non-aggregating fragments. An electrospray mass spectrometric study

The aggregation of full-length (residues 1-40) amyloid beta-peptide (A beta) and fragments corresponding to residues 1-23 and 24-40 was studied by electrospray mass spectrometry, using gramicidin as a non-aggregating reference. Following a lag period, A beta(1-40) at 140 microM concentration aggregates with apparent first-order kinetics. Under acidic conditions A beta(1-40) undergoes spontaneous cleavage between Asp23-Val24 and to a lesser extent also at two other Asp-X motifs. Incubation in acidic H(2)18O showed incorporation of 18O in fragment A beta(1-23), confirming that the Asp23-Val24 peptide bond had been hydrolyzed. Incubation of synthetic A beta(1-23) and A beta(24-40) peptides with A beta(1-40) showed that A beta(24-40) remained in solution for several months, that A beta(1-23) partly disappeared from solution, whereas A beta(1-40) completely disappeared. Further, treatment of sedimentable aggregates formed after co-incubation of the three peptides with hexafluoro-2-propanol or formic acid recovered the intensity of A beta(1-40). These data support previous studies showing that the region of A beta encompassing residues 16-24 is necessary for aggregation into amyloid fibrils.

The N-terminal Propeptide of Lung Surfactant Protein C is Necessary for Biosynthesis and Prevents Unfolding of a Metastable α-Helix

The lung surfactant-associated protein C (SP-C) consists mainly of a polyvaline alpha-helix, which is stable in a lipid membrane. However, in agreement with the predicted beta-strand conformation of a polyvaline segment, helical SP-C unfolds and transforms into beta-sheet aggregates and amyloid fibrils within a few days in aqueous organic solvents. SP-C fibril formation and aggregation have been associated with lung disease. Here, we show that in a recently isolated biosynthetic precursor of SP-C (SP-Ci), a 12 residue N-terminal propeptide locks the metastable polyvaline part in a helical conformation. The SP-Ci helix does not aggregate or unfold during several weeks of incubation, as judged by hydrogen/deuterium exchange and mass spectrometry. Hydrogen/deuterium exchange experiments further indicate that the propeptide reduces exchange in parts corresponding to mature SP-C. Finally, in an acidic environment, SP-Ci unfolds and aggregates into amyloid fibrils like SP-C. These data suggest a direct role of the N-terminal propeptide in SP-C biosynthesis.

Folding into a β-Hairpin Can Prevent Amyloid Fibril Formation

The tetrapeptide KFFE is one of the shortest amyloid fibril-forming peptides described. Herein, we have investigated how the structural environment of this motif affects polymerization. Using a turn motif (YNGK) or a less rigid sequence (AAAK) to fuse two KFFE tetrapeptides, we show by several biophysical methods that the amyloidogenic properties are strongly dependent on the structural environment. The dodecapeptide KFFEAAAKKFFE forms abundant thick fibril bundles. Freshly dissolved KFFEAAAKKFFE is monomeric and shows mainly disordered secondary structure, as evidenced by circular dichroism, NMR spectroscopy, hydrogen/deuterium exchange measurements, and molecular modeling studies. In sharp contrast, the dodecapeptide KFFEYNGKKFFE does not form fibrils but folds into a stable beta-hairpin. This structure can oligomerize into a stable 12-mer and multiples thereof, as shown by size exclusion chromatography, sedimentation analysis, and electrospray mass spectrometry. These data indicate that the structural context in which a potential fibril forming sequence is present can prevent fibril formation by favoring self-limiting oligomerization over polymerization.

Charge attraction and beta propensity are necessary for amyloid fibril formation from tetrapeptides

Amyloid fibrils in which specific proteins have polymerized into a cross-beta-sheet structure are found in about 20 diseases. In contrast to the close structural similarity of fibrils formed in different amyloid diseases, the structures of the corresponding native proteins differ widely. We show here that peptides as short as 4 residues with the sequences KFFE or KVVE can form amyloid fibrils that are practically identical to fibrils formed in association with disease, as judged by electron microscopy and Congo red staining. In contrast, KLLE or KAAE do not form fibrils. The fibril-forming KFFE and KVVE show partial beta-strand conformation in solution, whereas the non-fibril-forming KLLE and KAAE show random structure only, suggesting that inherent propensity for beta-strand conformation promotes fibril formation. The peptides KFFK or EFFE do not form fibrils on their own but do so in an equimolar mixture. Thus, intermolecular electrostatic interactions, either between charged dipolar peptides or between complementary charges of co-fibrillating peptides favor fibril formation.

Hydrogen/deuterium exchange and aggregation of a polyvaline and a polyleucine alpha-helix investigated by matrix-assisted laser desorption ionization mass spectrometry

The membrane-associated pulmonary surfactant protein C (SP-C), containing a polyvaline alpha-helix, and a synthetic SP-C analogue with a polyleucine helix (SP-C(Leu)) were studied by hydrogen/deuterium exchange matrix-assisted laser desorption ionization (MALDI) mass spectrometry. SP-C, but not SP-C(Leu), formed abundant amyloid fibrils under experimental conditions. In CD(3)OD/D(2)O, 91:9 (v/v), containing 2 mM ammonium acetate, SP-C(Leu) and SP-C exchanged 40% of their exchangeable hydrogens within 1 min. This corresponds to exchange of labile side-chain hydrogen atoms, hydrogens on the N- and C-terminal heteroatoms, and amide hydrogen atoms in the unstructured N-terminal regions. After approximately 300 h, four exchangeable hydrogen atoms in SP-C(Leu) and 10 in SP-C remained unexchanged. During this time period the ion current corresponding to singly charged SP-C decreased to <10% of the initial value due to the formation of insoluble aggregates that are not detected by MALDI mass spectrometry. In contrast, the ion current for SP-C(Leu) was maintained over this time period, although the peptides were incubated together. In combination, hydrogen/deuterium exchange and aggregation data indicate that the polyleucine peptide refolds into a helix after opening, while the unfolded polyvaline peptide forms insoluble beta-sheet aggregates rather than refolding into a helix. The SP-C helix, but not the SP-C(Leu) helix, is thus in a metastable state, which may contribute to the recently observed tendency of SP-C and its precursor to misfold and aggregate in vivo.