Plant Viruses As Biotemplates.....#Biopharamceutical #Plants #Viruses


Plant viruses have been investigated and utilized in biotechnology across a broad range of applications ranging from crop protection and improvement to protein production systems. A broad range of plant virus systems have become attractive for the generation of recombinant proteins, including vaccines, biopharmaceuticals, and industrial proteins. But now a novel application of virus has been observes that is the use of capsid. 


Viral capsid is considered as a Nano template due to its dimensions which range from 10s to 100s of nanometers. Hence the materials which are template by virus capsid also fall in the same range. The use of viruses as template, exploits its inherent properties such as infecting the host, replicate, pack its nucleic acid contents and then exit the cell. For this, viruses have high plasticity in nature that is its ability to survive harsh conditions, and manages the target delivery of its cargo whatever the conditions maybe. All such properties mimic our bio delivery systems.


Three interfaces of capsid can be exploited i. e. interior, exterior and interfaces between protein sub-unit. Capsids normally have highly symmetrical structure with several repeating sub-units. All viruses package, encode and transport nucleic acid. However, they are assembled into noninfectious cage devoid of genetic material.  


Size constrained environment is ideally provided by interior surface of viral capsid. This allows the nucleation or attachment of molecular or nanomaterials. This can be done in two ways. First, during capsid assembly, the guest molecule is entrapped. Second approach is the entrapment of guest molecule within already assembled capsid.  

Early work with CCMV demonstrated the use of capsids for synthesis of nano-materials as indicated in the figure. Inorganic nano-particles of anionic polyoxometalate salts were synthesized. However, cat-ionic compounds could not be synthesized in this manner due to the underlying positive charges in interior interface.

Helical rod shaped TMV capsid is proven to be useful in nano-wire synthesis. It is also attractive template for nano-rod synthesis. TMV assembly is inherently asymmetrical and hence distinct from spherical viral capsids. More recently, bimetallic alloys of CoPt3, CoPt and FePt3 nano-wires having length up to 100 nm and 4 nm diameters have been manufactured in the TMV capsid channel. Formation of small isolated nano-particles of Ni and Ag has also been reported.

An alternative approach is to make the assembly of capsid around the enzyme or preformed nano-particle. For example TMV has been directed to assemble around Aurum nano-particles having citrate intermediate layer between protein surface and Au. This is done to create complementary interaction between coat proteins sub-unit and citrate. But the encapsulation efficiency was low in this case. A subsequent effort with carboxylic terminated polyethylene glycol coated aurum particles demonstrated higher TMV encapsulation efficiency.


The exterior interface of viral capsid provides multivalent display of ligands in different spatial locations. Genetic and chemical modification of exterior surface allows the formation of several thousands of copies of functional groups and ligands. These functional groups act as attachment site. These groups react readily with small activated compounds.

The exterior surface of CPMV has been utilized for material synthesis. TMV exterior surface has been used for creation of nano-tubes and nano-particles. The tubes have been produced by depositing clusters of platinum, palladium and gold on exterior surface of TMV. This results in metallic coat on the virion which acts as base layer for electrodeposition of other metals such as cobalt and nickel. 


Gadolinium is used as MRI contrast agent in humans. Binding of Gd3+ in spatially defined fashion on a capsid creates a high concentration metallic environment. The atoms still have ability to bind water molecules creating relatively large capsid. This results in slow tumbling which creates enhanced MRI contrast agent.

Engineered plant viruses have been used for cell targeted delivery of therapeutics. An antimicrobial photodynamic therapy was upregulated by coupling the photosensitizer to cell targeting ligand. Genetic construct of protein cage allowed dual functionality with photosensitizer and targeting ligand.

Figure: CCMV targeted cell VS Control

Figure: CCMV targeted cell VS Control

With the help of flow cytometry, the targeted delivery of CCMV was demonstrated towards proteins A which was being expressed on the cells with Staphylococcus aureus. It was estimated that almost 3×103/µm2 were targeted to the cell walls within densely packed areas. TEM indicated that those CCMV were in close contact with targeted cell walls. Killing of the targeted cells was enhanced 100 folds as compared to free PS agent or non-targeted cells.

We are in the future of developing many products to really move to be cutting edge on the market.  Our research and development of many based elements will further encompass the reason why we want to develop more and more combination products.  

Reginald Swift