PhD Dissertation Defense by Priya Sridharan: "Investigating the Molecular Bases of the HIV-1 Nef-Mediated Hijacking of ALIX and PTPN23"
When: Tuesday,
December 17, 2024
9:00 AM
-
11:00 AM
Where: Science and Engineering Building 285 Old Westport Road, Dartmouth, MA
Description: Investigating the Molecular Bases of the HIV-1 Nef-Mediated Hijacking of ALIX and PTPN23 by Priya Sridharan
Date: Tuesday, December 17, 2024
Time: 9:00AM
Place: SENG 311
Abstract: HIV-1 Nef is a multifunctional accessory protein with a molecular mass of 27 kDa that plays a central role in lentiviral pathogenesis by manipulating the host cell's immune response to enhance viral replication. Nef influences a wide range of host cell processes, including signal transduction and vesicular transport pathways. One of its key functions is the downregulation of cell surface receptors, particularly CD4 and MHC class I (MHCI).
Nef downregulates CD4 by accelerating its endocytosis via the clathrin/AP-2 pathway. Subsequently, Nef targets CD4 to the multivesicular body (MVB) pathway for eventual delivery to lysosomes, a process involving the endosomal sorting complex required for transport (ESCRT) machinery. While the structural details of Nef-mediated AP2-dependent endocytosis of CD4 have been revealed previously, the process leading to CD4 retention in late endosomes and its CD4 degradation in lysosomes remain mechanistically unknown.
Research led by Dr. Luis L. P. da Silva at the University of Sao Paulo discovered that Nef directly interacts with Alix (apoptosis-linked gene 2-interacting protein X), a critical component of the ESCRT machinery, to enable lysosomal delivery of CD4. In this dissertation project, the Alix-Nef interaction was investigated using biochemical assays, revealing new insights into this interaction as well as Nef biology.
PTPN23, a putative protein tyrosine phosphatase and paralog of Alix, contains a protein tyrosine phosphatase (PTP) domain and a PEST motif, along with regions shared with Alix, namely the Bro1 domain, the coiled-coil (CC) domains, and a proline-rich region (PRR). Like Alix, PTPN23 supports ESCRT function and is a key regulator in endosomal sorting and vesicular trafficking. Unlike Alix, PTPN23 adopts an open, extended conformation that allows for simultaneous interactions with multiple ESCRT components. Preliminary data from our collaborator, Dr. John Guatelli's lab, suggests that PTPN23 is hijacked by HIV-1 Nef to facilitate receptor mistrafficking, presumably leading to the lysosomal degradation of cell surface receptors. Consequently, this mechanism could enhance viral immune evasion and pathogenesis. The potential binding interaction between Nef and PTPN23 was also investigated in this dissertation.
PhD Dissertation Committee: Dr. Xiaofei Jia (Advisor), Associate Professor (Chemistry/Biochemistry)
Dr. Tracie Ferreira, Associate Professor/Chair (Bioengineering)
Dr. Shuowei Cai, Professor (Chemistry/Biochemistry)
Dr. Christopher J Brigham, Associate Professor (Department of Bioengineering)
Date: Tuesday, December 17, 2024
Time: 9:00AM
Place: SENG 311
Abstract: HIV-1 Nef is a multifunctional accessory protein with a molecular mass of 27 kDa that plays a central role in lentiviral pathogenesis by manipulating the host cell's immune response to enhance viral replication. Nef influences a wide range of host cell processes, including signal transduction and vesicular transport pathways. One of its key functions is the downregulation of cell surface receptors, particularly CD4 and MHC class I (MHCI).
Nef downregulates CD4 by accelerating its endocytosis via the clathrin/AP-2 pathway. Subsequently, Nef targets CD4 to the multivesicular body (MVB) pathway for eventual delivery to lysosomes, a process involving the endosomal sorting complex required for transport (ESCRT) machinery. While the structural details of Nef-mediated AP2-dependent endocytosis of CD4 have been revealed previously, the process leading to CD4 retention in late endosomes and its CD4 degradation in lysosomes remain mechanistically unknown.
Research led by Dr. Luis L. P. da Silva at the University of Sao Paulo discovered that Nef directly interacts with Alix (apoptosis-linked gene 2-interacting protein X), a critical component of the ESCRT machinery, to enable lysosomal delivery of CD4. In this dissertation project, the Alix-Nef interaction was investigated using biochemical assays, revealing new insights into this interaction as well as Nef biology.
PTPN23, a putative protein tyrosine phosphatase and paralog of Alix, contains a protein tyrosine phosphatase (PTP) domain and a PEST motif, along with regions shared with Alix, namely the Bro1 domain, the coiled-coil (CC) domains, and a proline-rich region (PRR). Like Alix, PTPN23 supports ESCRT function and is a key regulator in endosomal sorting and vesicular trafficking. Unlike Alix, PTPN23 adopts an open, extended conformation that allows for simultaneous interactions with multiple ESCRT components. Preliminary data from our collaborator, Dr. John Guatelli's lab, suggests that PTPN23 is hijacked by HIV-1 Nef to facilitate receptor mistrafficking, presumably leading to the lysosomal degradation of cell surface receptors. Consequently, this mechanism could enhance viral immune evasion and pathogenesis. The potential binding interaction between Nef and PTPN23 was also investigated in this dissertation.
PhD Dissertation Committee: Dr. Xiaofei Jia (Advisor), Associate Professor (Chemistry/Biochemistry)
Dr. Tracie Ferreira, Associate Professor/Chair (Bioengineering)
Dr. Shuowei Cai, Professor (Chemistry/Biochemistry)
Dr. Christopher J Brigham, Associate Professor (Department of Bioengineering)
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