Coagulation factor binding orientation and dimerization may influence infectivity of adenovirus-coagulation factor...

Area of Science:

• Biotechnology
• Molecular Biology
• Virology

Background:

• Adenoviruses (Ads) are utilized as therapeutic vectors.
• Ad vectors injected into the bloodstream can bind vitamin K-dependent blood coagulation factors, leading to liver sequestration and hepatocyte transduction.
• Both coagulation factors FVII and FX bind the hexon protein of human Ad serotype 5 (HAdv5) with high affinity, but only FX mediates Ad-hepatocyte transduction in vivo.

Purpose of the Study:

• To investigate the discrepancy between FVII's high-affinity binding to HAdv5 hexon and its poor capacity for supporting virus cell entry.
• To elucidate the structural basis for differential infectivity between Ad-FX and Ad-FVII complexes.

Main Methods:

• High-resolution cryo-electron microscopy (cryo-EM) of the HAdv5-FVII complex.
• Molecular dynamic flexible fitting (MDFF) simulations.
• Analysis of hexon-coagulation factor interactions and structural orientations.

Main Results:

• Hexon amino acids T423, E424, and T425 are involved in both FVII and FX binding.
• The FVII GLA domain binds to the hexon trimer depression in a different orientation compared to FX.
• Two proximal FVII molecules dimerize via their serine protease (SP) domains when bound to hexon, burying potential heparan sulfate proteoglycan (HSPG) receptor binding residues.
• No FVII dimerization was observed in earlier cryo-EM studies of the Ad-FX interaction.

Conclusions:

• FVII binding to HAdv5 hexon leads to dimerization, which may mask essential receptor binding sites.
• This FVII-hexon complex dimerization is a potential mechanistic reason for the differential infectivity of Ad-FX and Ad-FVII complexes, despite similar binding affinities.
• Understanding these interactions is crucial for optimizing adenovirus vector-based therapies.