Production of VNPs, VLPs, and Chimeras - Viral Nanoparticles: Tools for Materials Science and Biomedicine - page 55

b

for particles. Here, azide- or

alkyne-containing unnatural amino acids were successfully incorporated into
the viral coat proteins (Strable

Hepatitis B virus (HBV) core particles

1

and Q

, 2008). The azide or alkyne functional
group allows chemical modification of the particles using Cu-catalyzed
azide-alkyne cycloadditions (click chemistry), a highly specific and effective
functionalization method (discussed in Chapter 4).

et al.

Figure 3.2 Methionine and analogs azidohomoalanine and homopropargylglycine.

In brief, genetic engineering was used to insert Met codons at positions
where the unnatural amino acid is desired. The modified plasmids are
transformed into

After initial growth with natural amino acids, Met is
removedfromthecellmediaandreplacedwiththeazide-oralkyne-containing
unnatural amino acids azidohomoalanine and homopropargylglycine
(Fig. 3.2). At this stage, expression of the viral coat proteins is induced,
which leads to incorporation of the amino acid analogous into the capsid
proteins. Using this strategy, intact virions containing novel azide- or alkyne-
functionality on the capsid surface were self-assembled and isolated from
the bacteria. Recombinant particles were chemically functionalized using
click reactions (Strable

E. coli.

et al. , 2008).

.. yeast expression Systems

Yeast expression systems have been widely used, and expression systems
have been developed for a range of species including

Saccharomyces

cerevisiae , the genetics, biochemistry,

and molecular biology of yeast have been extensively studied. With this
knowledge in hand, various commercially available kits have been developed
1

and Pichia pastoris . Similar to E. coli

infects the liver, causing inflammation that is referred to as hepatitis. HBV core
particles are non-infectious particles formed during HBV infection. HBV cores or capsids are
immunogenic as they consist of the surface antigen protein. HBV core particles play an important
role in vaccine development.

Hepatitis B virus