Protein interactions of membrane protein U24 from Roseolovirus and implications for its function

This dissertation describes the investigation of the interactions between the tail-anchored membrane protein U24 from Human Herpesvirus type 6A (HHV-6A) and type 7 (HHV-7) and its potential binding partners. The roles that these interactions play in U24s’ function will be presented. It has been suggested that U24 from HHV-6A (U24-6A) may trigger an autoimmune reaction in multiple sclerosis (MS), through its molecular mimicry of myelin basic protein (MBP). Both versions of U24 have been implicated in endocytic recycling via specific binding partners, namely WW domains. The first part of this thesis is a review of the foundations that this thesis is based on, from the description of Roseoloviruses, associated diseases to molecular characterizations. The two main techniques used in the studies will be described as well. Prior to commencing any structural or interaction studies, a protocol is devised to express and purify recombinant U24 from HHV-7 (U24-7), as well as preliminary studies to prepare samples suitable for structure determination by nuclear magnetic resonance (NMR) spectroscopy. U24-6A was shown to be a mimic of MBP and it was suggested that it could be implicated in MS by competing with MBP for its interactions, such as the interactions with Fyn-SH3 domain. The interactions between U24-6A and Fyn-SH3 domain were therefore probed and found to be weak, calling into question this mimicry hypothesis. Because of the weak binding with Fyn-SH3 domain, alternative functions and binding partners were then explored. WW domains were chosen because their binding ligand, the PPxY (PY) motif, is present in U24 and was identified to be essential for U24’s function. In the next part of this thesis, the investigation of the interactions between U24s and WW domains in Nedd4, which is a key component required for endocytosis, are described. U24-7 and phosphorylated U24-6A were found to bind strongly to Nedd4-WW domains, suggesting the negative charge upstream from PY motif in U24 is important for high affinity interactions. Non-canonical Smurf2 WW domains were explored as well. Finally, the results presented in this thesis will be discussed in the context of the function of U24.Science, Faculty ofChemistry, Department ofGraduat

Viral Proteins with PxxP and PY Motifs May Play a Role in Multiple Sclerosis

Multiple sclerosis (MS) is a debilitating disease that arises from immune system attacks to the protective myelin sheath that covers nerve fibers and ensures optimal communication between brain and body. Although the cause of MS is unknown, a number of factors, which include viruses, have been identified as increasing the risk of displaying MS symptoms. Specifically, the ubiquitous and highly prevalent Epstein–Barr virus, human herpesvirus 6, cytomegalovirus, varicella–zoster virus, and other viruses have been identified as potential triggering agents. In this review, we examine the specific role of proline-rich proteins encoded by these viruses and their potential role in MS at a molecular level.Science, Faculty ofAlumniChemistry, Department ofReviewedFacult

U24 from Roseolovirus interactions with WW Domains: Canonical vs Non-Canonical

U24 is a C-terminal membrane-anchored protein found in both Human Herpes Virus type 6 and 7 (HHV-6 and HHV-7), with an N-terminal segment that is rich in prolines (PPxY motif in both HHV-6A and 7; PxxP motif in HHV-6A). Previous work has shown that U24 interacts strongly with Nedd4 WW domains, in particular hNedd4L-WW3*. It was also shown that this interaction depends strongly on the nature of the amino acids that are upstream from the PY motif in U24. In this contribution, data was obtained from pull-downs, isothermal titration calorimetry, and NMR to further determine what modulates U24:WW domain interactions. Specifically, three non-canonical WW domains from human Smad ubiquitination regulatory factor (Smurf), namely hSmurf2-WW2, hSmurf2-WW3, and a tandem construct hSmurf2-WW2+3, were studied. Overall, the interactions between U24 and these Smurf WW domains were found to be weaker than those in U24:Nedd4 WW domain pairs, suggesting that U24 function is tightly linked to specific E3 ubiqitin ligases.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Studying the Interactions of U24 from HHV-6 in Order to Further Elucidate Its Potential Role in MS

A number of studies have suggested that human herpesvirus 6A (HHV-6A) may play a role in multiple sclerosis (MS). Three possible hypotheses have been investigated: (1) U24 from HHV-6A (U24-6A) mimics myelin basic protein (MBP) through analogous phosphorylation and interaction with Fyn-SH3; (2) U24-6A affects endocytic recycling by binding human neural precursor cell (NPC) expressed developmentally down-regulated protein 4-like WW3* domain (hNedd4L-WW3*); and (3) MS patients who express Killer Cell Immunoglobulin Like Receptor 2DL2 (KIR2DL2) on natural killer (NK) cells are more susceptible to HHV-6 infection. In this contribution, we examined the validity of these propositions by investigating the interactions of U24 from HHV-6B (U24-6B), a variant less commonly linked to MS, with Fyn-SH3 and hNedd4L-WW3* using heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR) titrations and isothermal titration calorimetry (ITC). In addition, the importance of phosphorylation and the specific role of U24 in NK cell activation in MS patients were examined. Overall, the findings allowed us to shed light into the models linking HHV-6 to MS and the involvement of U24

T-Cell Responses to COVID-19 Vaccines and Breakthrough Infection in People Living with HIV Receiving Antiretroviral Therapy

People living with HIV (PLWH) can exhibit impaired immune responses to vaccines. Accumulating evidence indicates that PLWH, particularly those receiving antiretroviral therapy, mount strong antibody responses to COVID-19 vaccines, but fewer studies have examined cellular immune responses to the vaccinations. Here, we used an activation-induced marker (AIM) assay to quantify SARS-CoV-2 spike-specific CD4+ and CD8+ T cells generated by two and three doses of COVID-19 vaccines in 50 PLWH receiving antiretroviral therapy, compared to 87 control participants without HIV. In a subset of PLWH, T-cell responses were also assessed after post-vaccine breakthrough infections and/or receipt of a fourth vaccine dose. All participants remained SARS-CoV-2 infection-naive until at least one month after their third vaccine dose. SARS-CoV-2 infection was determined by seroconversion to a Nucleocapsid (N) antigen, which occurred in 21 PLWH and 38 control participants after the third vaccine dose. Multivariable regression analyses were used to investigate the relationships between sociodemographic, health- and vaccine-related variables, vaccine-induced T-cell responses, and breakthrough infection risk. We observed that a third vaccine dose boosted spike-specific CD4+ and CD8+ T-cell frequencies significantly above those measured after the second dose (all p 0.1), but CD8+ T-cell responses were modestly lower in PLWH after the third dose (p = 0.02), an observation that remained significant after adjusting for sociodemographic, health- and vaccine-related variables (p = 0.045). In PLWH who experienced a breakthrough infection, median T-cell frequencies increased even higher than those observed after three vaccine doses (p < 0.03), and CD8+ T-cell responses in this group remained higher even after a fourth vaccine dose (p = 0.03). In multivariable analyses, the only factor associated with an increased breakthrough infection risk was younger age, which is consistent with the rapid increase in SARS-CoV-2 seropositivity that was seen among younger adults in Canada after the initial appearance of the Omicron variant. These results indicate that PLWH receiving antiretroviral therapy mount strong T-cell responses to COVID-19 vaccines that can be enhanced by booster doses or breakthrough infection.Medicine, Faculty ofNon UBCFamily Practice, Department ofMedicine, Department ofPathology and Laboratory Medicine, Department ofReviewedFacultyResearche