Structural Studies of Cytomegalovirus Entry Proteins
cytomegalovirus (HCMV), a dsDNA, enveloped virus, is a ubiquitous pathogen that
establishes lifelong latent infections in 50-90% of the population. It causes disease in
persons with compromised immune systems, e.g., organ transplant recipients or AIDS
patients. HCMV is also a leading cause of congenital viral infections and developmental
defects in newborns. Entry of HCMV into... read morecells requires the conserved glycoprotein B
(gB), thought to function as a fusogen and reported to bind signaling receptors. gB also
elicits a strong immune response in humans and induces the production of neutralizing
antibodies, although most anti-gB antibodies are non-neutralizing. The crystal structure
of the HCMV gB ectodomain determined to 3.6-Å resolution presented in this work is
the first atomic-level structure of any betaherpesvirus glycoprotein. The structure of
HCMV gB resembles the postfusion structures of HSV-1 and EBV homologs, establishing it
as a new member of the class III viral fusogens. Despite structural similarities, each
gB has a unique domain arrangement, demonstrating structural plasticity of gB that may
accommodate virus-specific functional requirements. The structure illustrates how
extensive glycosylation of the gB ectodomain influences antibody recognition. Antigenic
sites that elicit neutralizing antibodies are more heavily glycosylated than those that
elicit non-neutralizing antibodies, which suggest that HCMV gB uses glycans to shield
neutralizing epitopes while exposing non-neutralizing epitopes to act as an immune
decoy. This glycosylation pattern may have evolved to direct the immune response towards
the generation of non-neutralizing antibodies thus helping HCMV to avoid clearance. The
structure provided the framework for understanding the antigenic regions (AD1-5) of the
protein, however, clinical information was needed to know which region would generate
antibodies leading to protection in humans. By determining the level of antibodies
against each antigenic region present in maternal sera from mothers of premature
infants, we identified two trends affecting the ability of these antibodies to protect.
The presence of antibodies against AD-5 correlated with protection from infection while
the presence of antibodies against AD-1 interfered with protection. The latter was
stronger and overcame the beneficial effects of anti-AD-5 antibodies. These trends await
confirmation with larger sample sizes, yet they along with the HCMV gB structure offer
valuable insights that may aid in the design of recombinant vaccines and monoclonal
Thesis (Ph.D.)--Tufts University, 2017.
Submitted to the Dept. of Molecular Microbiology.
Advisors: Ekaterina Heldwein, and Ralph Isberg.
Committee: David Snydman, Andrew Bohm, and Marta Gaglia.
Keywords: Virology, and Biochemistry.read less