A conservative mutant of a proteolytic fragment produced during fibril formation enhances fibrillogenesis

Old dog, new tricks: Influenza A virus NS1 and in vitro fibrillogenesis

The influenza NS1 protein is involved in suppression of the host immune response. Recently, there is growing evidence that prion-like protein aggregation plays an important role in cellular signaling and immune responses. In this work, we obtained a recombinant, influenza A NS1 protein and showed that it is able to form amyloid-like fibrils in vitro. Using proteolysis and subsequent mass spectrometry, we showed that regions resistant to protease hydrolysis highly differ between the native NS1 form (NS1-N) and fibrillar form (NS1-F); this indicates that significant structural changes occur during fibril formation. We also found a protein fragment that is capable of inducing the process of fibrillogenesis at 37 °C. The discovery of the ability of NS1 to form amyloid-like fibrils may be relevant to uncovering relationships between influenza A infection and modulation of the immune response.

Nicking and fragmentation are responsible for α-lactalbumin amyloid fibril formation at acidic pH and elevated temperature

Amyloid fibrils are ordered aggregates that may be formed from disordered, partially unfolded, and fragments of proteins and peptides. There are several diseases, which are due to the formation and deposition of insoluble β-sheet protein aggregates in various tissue, collectively known as amyloidosis. Here, we have used bovine α-lactalbumin as a model protein to understand the mechanism of amyloid fibril formation at pH 1.6 and 65°C under non-reducing conditions. Amyloid fibril formation is confirmed by Thioflavin T fluorescence and atomic force microscopy (AFM). Our finding demonstrates that hydrolysis of peptide bonds occurs under these conditions, which results in nicking and fragmentation. The nicking and fragmentation have been confirmed on non-reducing and reducing gel. We have identified the fragments by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. The fragmentation may initiate nucleation as it coincides with AFM images. Conformational changes associated with monomer resulting in fibrillation are shown by circular dichroism and Raman spectroscopy. The current study highlights the importance of nicking and fragmentation in amyloid fibril formation, which may help understand the role of acidic pH and proteolysis under in vivo conditions in the initiation of amyloid fibril formation.

α-Lactalbumin, Amazing Calcium-Binding Protein

α-Lactalbumin (α-LA) is a small (Mr 14,200), acidic (pI 4–5), Ca²⁺-binding protein. α-LA is a regulatory component of lactose synthase enzyme system functioning in the lactating mammary gland. The protein possesses a single strong Ca²⁺-binding site, which can also bind Mg²⁺, Mn²⁺, Na⁺, K⁺, and some other metal cations. It contains several distinct Zn²⁺-binding sites. Physical properties of α-LA strongly depend on the occupation of its metal binding sites by metal ions. In the absence of bound metal ions, α-LA is in the molten globule-like state. The binding of metal ions, and especially of Ca²⁺, increases stability of α-LA against the action of heat, various denaturing agents and proteases, while the binding of Zn²⁺ to the Ca²⁺-loaded protein decreases its stability and causes its aggregation. At pH 2, the protein is in the classical molten globule state. α-LA can associate with membranes at neutral or slightly acidic pH at physiological temperatures. Depending on external conditions, α-LA can form amyloid fibrils, amorphous aggregates, nanoparticles, and nanotubes. Some of these aggregated states of α-LA can be used in practical applications such as drug delivery to tissues and organs. α-LA and some of its fragments possess bactericidal and antiviral activities. Complexes of partially unfolded α-LA with oleic acid are cytotoxic to various tumor and bacterial cells. α-LA in the cytotoxic complexes plays a role of a delivery carrier of cytotoxic fatty acid molecules into tumor and bacterial cells across the cell membrane. Perhaps in the future the complexes of α-LA with oleic acid will be used for development of new anti-cancer drugs.

Plasma exosomes stimulate breast cancer metastasis through surface interactions and activation of FAK signaling

PURPOSE

The interaction between malignant cells and surrounding healthy tissues is a critical factor in the metastatic progression of breast cancer (BC). Extracellular vesicles, especially exosomes, are known to be involved in inter-cellular communication during cancer progression. In the study presented herein, we aimed to evaluate the role of circulating plasma exosomes in the metastatic dissemination of BC and to investigate the underlying molecular mechanisms of this phenomenon.

METHODS

Exosomes isolated from plasma of healthy female donors were applied in various concentrations into the medium of MDA-MB-231 and MCF-7 cell lines. Motility and invasive properties of BC cells were examined by random migration and Transwell invasion assays, and the effect of plasma exosomes on the metastatic dissemination of BC cells was demonstrated in an in vivo zebrafish model. To reveal the molecular mechanism of interaction between plasma exosomes and BC cells, a comparison between un-treated and enzymatically modified exosomes was performed, followed by mass spectrometry, gene ontology, and pathway analysis.

RESULTS

Plasma exosomes stimulated the adhesive properties, two-dimensional random migration, and transwell invasion of BC cells in vitro as well as their in vivo metastatic dissemination in a dose-dependent manner. This stimulatory effect was mediated by interactions of surface exosome proteins with BC cells and consequent activation of focal adhesion kinase (FAK) signaling in the tumor cells.

CONCLUSIONS

Plasma exosomes have a potency to stimulate the metastasis-promoting properties of BC cells. This pro-metastatic property of normal plasma exosomes may have impact on the course of the disease and on its prognosis.

Peptide-Induced Amyloid-Like Conformational Transitions in Proteins

Changes in protein conformation can occur both as part of normal protein functioning and during disease pathogenesis. The most common conformational diseases are amyloidoses. Sometimes the development of a number of diseases which are not traditionally related to amyloidoses is associated with amyloid-like conformational transitions of proteins. Also, amyloid-like aggregates take part in normal physiological processes such as memorization and cell signaling. Several primary structural features of a protein are involved in conformational transitions. Also the protein proteolytic fragments can cause the conformational transitions in the protein. Short peptides which could be produced during the protein life cycle or which are encoded by short open reading frames can affect the protein conformation and function.