Date of Award

Spring 5-15-2020

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Biochemistry)

Degree Name

Doctor of Philosophy (PhD)

Degree Type



Poxviruses are characterized by large double stranded DNA genomes that encode numerous proteins tailored for host immune response evasion. Our lab has been investigating a sequence-diverse family of secreted poxvirus proteins that appear to share a conserved beta-sandwich fold, but differ in their immunomodulatory functions. We have termed members of this superfamily Poxvirus Immune Evasion (PIE) proteins, and there appears to be at least 20 distinct subfamilies. As it turns out, cowpox virus (CPXV) encodes 10 PIE proteins, one of which, M2, can inhibit murine T cell activation through specific interactions with co-stimulatory ligands B7. 1 (CD80) and B7. 2 (CD86). Functionally, weնe shown that CPXV M2 selectively blocks murine B7. 2/CD28 interaction. Using surface plasmon resonance (SPR), Iնe demonstrated that CPXV M2 has a preferential interaction with mB7. 2 over mB7. 1 which allows the predominantly inhibitory molecule, mB7. 1, to continue interaction with mCTLA-4. Cryo-EM analysis of CPXV M2, in complex with human B7s, reveals the formation of both hexameric and heptameric ringed structures linked via intermolecular disulfide bonds. These oligomers are constitutively expressed and secreted with the capability of binding one B7 molecule per monomer. Size exclusion coupled light scatter, native mass spectroscopy, negative stain EM, and native PAGE all support the formation of these oligomeric species in both B7-bound and unbound CPXV M2. Additionally, oligomerization is conserved in at least three other poxvirus M2 analogs (MYXV, YKV, VACV WR), each of which has their own B7 species specificity. Together, our data helps define a novel mechanism by which CPXV exploits cellular ligands to selectively shut down host T cell activation.


English (en)

Chair and Committee

Daved H. Fremont

Committee Members

Wayne Yokoyama, Michael Diamond, Thomas Brett, Jeffrey Henderson,