Investigation into the Role of the Infectious Bronchitis Virus (IBV) Envelope Protein in Viral Replication and Pathogenicity.

Abstract

Infectious bronchitis virus (IBV) is a highly infectious Gammacoronavirus, causing
respiratory disease in poultry. The IBV virion consists of four structural proteins: spike
(S), membrane (M), nucleocapsid (N) and envelope (E). The E protein has been
shown to function in viral assembly, release, and pathogenesis. Two forms of E are
found in infected cells: monomeric and a pentameric ion channel. Two mutations,
T16A and A26F, select for either the pentameric or monomeric form, respectively.
Previous work reports that these two mutations abolish E protein ion channel activity.
Using reverse genetics, either the mutation T16A or A26F were incorporated in a
non-pathogenic (Beau-R) or pathogenic (M41-K) IBV backbone. The resulting rIBVs
were assessed in relation to genetic stability, replication and cytopathogenicity.
Characterisation of the Beau-R based rIBVs, BeauR-T16A and BeauR-A26F
respectively, identified that the effect of these mutations was dependent on cell-type.
Generation of the T16A and A26F mutations in a pathogenic strain, M41-K, aimed to
investigate these mutations as vaccine targets. The rIBV M41K-A26F was unable to
be rescued suggesting the monomeric form of E is essential for viral replication.
Additionally, isolates of rIBV M41K-T16A, unlike BeauR-T16A generated mutations
in the S and M proteins, which may have been compensatory and potentially
facilitated replication. This indicates that these mutations may have a straindependent effect. M41K-T16A retained pathogenicity in vivo however the potential
role of additional mutations in genome needs to be investigated further. To investigate
the role of the E protein in the assembly and release of virus, mass spectrometry,
bioimaging techniques and cellular inhibitors were used. This thesis furthers
knowledge on the function of the coronavirus E protein during infection and
demonstrates that both the cell-type and IBV strain are important considerations for
the future study of the E protein in IBV replication.

Date of Award	21 Mar 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	Erica Bickerton (Supervisor), Helena Maier (Supervisor) & Andrew D Davidson (Supervisor)