Characterization of interaction between blood coagulation factor VIII and LRP1 suggests dynamic binding by alternating complex contacts

BACKGROUND

Deficiency in blood coagulation factor VIII (FVIII) results in life-threating bleeding (hemophilia A) treated by infusions of FVIII concentrates. To improve disease treatment, FVIII has been modified to increase its plasma half-life, which requires understanding mechanisms of FVIII catabolism. An important catabolic actor is hepatic low density lipoprotein receptor-related protein 1 (LRP1), which also regulates many other clinically significant processes. Previous studies showed complexity of FVIII site for binding LRP1.

OBJECTIVES

To characterize binding sites between FVIII and LRP1 and suggest a model of the interaction.

METHODS

A series of recombinant ligand-binding complement-type repeat (CR) fragments of LRP1 including mutated variants was generated in a baculovirus system and tested for FVIII interaction using surface plasmon resonance, tissue culture model, hydrogen-deuterium exchange mass spectrometry, and in silico.

RESULTS

Multiple CR doublets within LRP1 clusters II and IV were identified as alternative FVIII-binding sites. These interactions follow the canonical binding mode providing major binding energy, and additional weak interactions are contributed by adjacent CR domains. A representative CR doublet was shown to have multiple contact sites on FVIII.

CONCLUSIONS

FVIII and LRP1 interact via formation of multiple complex contacts involving both canonical and non-canonical binding combinations. We propose that FVIII-LRP1 interaction occurs via switching such alternative binding combinations in a dynamic mode, and that this mechanism is relevant to other ligand interactions of the low-density lipoprotein receptor family members including LRP1.

Characterization of protein unable to bind von Willebrand factor in recombinant factor VIII products

BACKGROUND

Therapeutic products with coagulation factor VIII (FVIII) have a wide range of specific activities, implying presence of protein with altered structure. Previous studies showed that recombinant FVIII products (rFVIII) contain a fraction (FVIIIFT ) unable to bind von Willebrand factor (VWF) and reported to lack activity. Because of loss of function(s), FVIIIFT can be defined as a product-related impurity, whose properties and levels in rFVIII products should be investigated.

OBJECTIVE

To isolate and characterize the FVIIIFT fraction in rFVIII products.

METHODS

Protein fractions unable (FVIIIFT ) and able (FVIIIEL ) to bind VWF were isolated from rFVIII products using immobilized VWF affinity chromatography (IVAC) and characterized by gel electrophoresis, immunoblotting, FVIII activity test, surface plasmon resonance, mass spectrometry, and for plasma clearance in mice.

RESULTS AND CONCLUSIONS

A robust IVAC methodology was developed and applied for analysis of 10 rFVIII products marketed in the United States. FVIIIFT was found at various contents (0.4%-21.5%) in all products. Compared with FVIIIEL , FVIIIFT had similar patterns of polypeptide bands by gel electrophoresis, but lower functional activity. In several representative products, FVIIIFT was found to have reduced sulfation at Tyr1680, important for VWF binding, decreased interaction with a low-density lipoprotein receptor-related protein 1 fragment, and faster plasma clearance in mice. These findings provide basic characterization of FVIIIFT and demonstrate a potential for IVAC to control this impurity in rFVIII products to improve their efficacy in therapy of hemophilia A.

[Influence of various bacterial ligand application methods on cytokine expression]

AIM

Study the production of cytokines in mice during vaccination with polycomponent Immunovac-VP-4 vaccine containing TLR ligands with various administration methods.

MATERIALS AND METHODS

Immunovac-VP-4 was administered to mice by subcutaneous, intranasal or per oral methods. The preparation was administered nasally at a single dose of 500 microg in the volume of 30 microl. Per oral single dose was 2000 microg in the volume of 0.5 ml. 200 microg of the preparation was administered subcutaneously. Cytokines in blood sera were determined by EIA 8 hours after the administration of the vaccine.

RESULTS

In mice 8 hours afterthe single administration of Immunovac-VP-4 the levels of IL-1beta, IL-6, IL- 12, IL-5 increased significantly. However their concentration differed depending on the method of administration. The most active expression of cytokines was observed during subcutaneous administration. The indexes of cytokine expression were significantly higher (p < 0.05) than during non-parenteral administration methods.

CONCLUSION

Mucosal application methods along with parenteral were established to be able to activate effector mechanisms of immune repose with its consequent polarization by Th1/Th2 pathways. These mechanisms lay the groundwork for development of antigen-specific immune responses against antigens/pathogens.

[Prenylation: from bacteria to eukaryotes]

For their protection from host cell immune defense, intracellular eukaryotic parasites developed a variety of mechanisms, including secretion systems III and IV which inject bacterial effectors directly into eukaryotic cells. These effectors may be posttranslational modified by host cell machinery and may function inside the host cell. Recently, to the list of possible posttranslational modifications of bacterial proteins the prenylation was added. In this work we describe current state of the knowledge about the prenylation of eukaryotic and prokaryotic proteins and its inhibitors. The bioinformatics analyses suggest possibility of prenylation for a number of Francisella genus proteins.