SUMMARY During infection of the nervous system, alphaherpesviruses, including pseudorabies virus (PRV) use retrograde axonal transport to travel towards the neuronal cell body and anterograde transport to traffic back to the cell periphery upon reactivation from latency. The PRV protein Us9 plays an essential but unknown role in anterograde viral spread. To determine Us9 function, we identified viral and host proteins that interact with Us9 and explored the role of KIF1A, a microtubule-dependent kinesin-3 motor involved in axonal sorting and transport. Viral particles are co-transported with KIF1A in axons of primary rat superior cervical ganglion neurons and overexpression or disruption of KIF1A function respectively increases and reduces anterograde capsid transport. Us9 and KIF1A interact early during infection with the aid of additional viral protein(s) but exhibit diminished binding at later stages when capsids typically stall in axons. Thus, alphaherpesviruses repurpose the axonal transport and sorting pathway to spread within their hosts.

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Pseudorabies virus (PRV), a member of the Alphaherpesvirinae, has a complex multilayered extracellular virion that is structurally conserved among other herpesviruses. PRV virions contain a double-stranded DNA genome within a proteinaceous capsid surrounded by the tegument, a layer of viral and cellular proteins. The envelope layer, which encloses the capsid and tegument, contains viral transmembrane proteins anchored in a phospholipid bilayer. The viral and host proteins contained within virions execute important functions during viral spread and pathogenesis, but a detailed understanding of the composition of PRV virions has been lacking. In this report, we present the first comprehensive proteomic characterization of purified PRV virions by mass spectrometry using two complementary approaches. To exclude proteins present in the extracellular medium that may nonspecifically associate with virions, we also analyzed virions treated with proteinase K and samples prepared from mock-infected cells. Overall, we identified 47 viral proteins associated with PRV virions, 40 of which were previously localized to the capsid, tegument, and envelope layers using traditional biochemical approaches. Additionally, we identified seven viral proteins that were previously undetected in virions, including pUL8, pUL20, pUL32, pUL40 (RR2), pUL42, pUL50 (dUTPase), and Rsp40/ICP22. Furthermore, although we did not enrich for posttranslational modifications, we detected phosphorylation of four virion proteins: pUL26, pUL36, pUL46, and pUL48. Finally, we identified 48 host proteins associated with PRV virions, many of which have known functions in important cellular pathways such as intracellular signaling, mRNA translation and processing, cytoskeletal dynamics, and membrane organization. This analysis extends previous work aimed at determining the composition of herpesvirus virions and provides novel insights critical for understanding the mechanisms underlying PRV entry, assembly, egress, spread, and pathogenesis.Pseudorabies virus (PRV) is a swine alphaherpesvirus closely related to the human pathogens herpes simplex virus type 1 and 2 (HSV-1 and HSV-2) and varicella-zoster virus (VZV) (96,113). PRV is a pantropic, neuroinvasive virus with a broad host range and has been used extensively as a powerful tool for studying the architecture of mammalian neuronal circuits (35). The infectious particle of PRV, known as the mature virion, is a multilayered structure that is conserved among all herpesvirus families. At the core of the virion is a linear doublestranded DNA genome that is packaged within a proteinaceous capsid. The capsid is surrounded by a layer of viral and cellular proteins known as the tegument, which is enclosed within a phospholipid bilayer studded with viral transmembrane proteins and is known as the virion envelope (96, 113). To understand the fundamental mechanisms underlying PRV spread and pathogenesis, a comprehensive understanding of the subunits that compose the highly complex virion structure is necessary.The ini...

The PTEN-induced putative kinase 1 (PINK1)/Parkin pathway can tag damaged mitochondria and trigger their degradation by mitophagy. Before the onset of mitophagy, the pathway blocks mitochondrial motility by causing Miro degradation. PINK1 activates Parkin by phosphorylating both Parkin and ubiquitin. PINK1, however, has other mitochondrial substrates, including Miro (also called RhoT1 and -2), although the significance of those substrates is less clear. We show that mimicking PINK1 phosphorylation of Miro on S156 promoted the interaction of Parkin with Miro, stimulated Miro ubiquitination and degradation, recruited Parkin to the mitochondria, and via Parkin arrested axonal transport of mitochondria. Although Miro S156E promoted Parkin recruitment it was insufficient to trigger mitophagy in the absence of broader PINK1 action. In contrast, mimicking phosphorylation of Miro on T298/T299 inhibited PINK1-induced Miro ubiquitination, Parkin recruitment, and Parkin-dependent mitochondrial arrest. The effects of the T298E/T299E phosphomimetic were dominant over S156E substitution. We propose that the status of Miro phosphorylation influences the decision to undergo Parkin-dependent mitochondrial arrest, which, in the context of PINK1 action on other substrates, can restrict mitochondrial dynamics before mitophagy.is the second most common neurodegenerative disorder, and is closely linked to mitochondrial dysfunction (1, 2). Two hereditary forms of recessive PD are caused by mutations in PINK1 (PTEN-induced putative kinase 1), a Ser/Thr mitochondrial kinase, and Parkin, a cytosolic E3 ubiquitin ligase (3, 4). The realization that these proteins are in a single pathway, with PINK1 acting upstream of Parkin to influence mitochondrial properties, was a critical step in uncovering the underlying pathological mechanisms of PD (5-7). This pathway can trigger the selective autophagy of damaged mitochondria, termed mitophagy (8, 9), but additional cellular functions have also been indicated for PINK1 and Parkin (10-15). Much, however, remains unclear about how the PINK1/Parkin pathway is regulated.In current models of PINK1/Parkin mitophagy (reviewed in ref. 1), healthy mitochondria import a PINK1 precursor constitutively to the inner membrane, where it is cleaved (16-18). The cleaved form then returns to the cytoplasm and is degraded by the N-end rule pathway (19). Mitochondrial depolarization, or protein misfolding in the matrix of energized mitochondria (20), prevent the import and degradation of PINK1, resulting in the accumulation of PINK1 on the outer mitochondrial membrane (OMM) (9,21,22). Once on the OMM, PINK1 kinase activity recruits Parkin from the cytosol (8, 9). Although Parkin adopts a self-inhibited conformation in solution (23-25), it becomes fully activated in a PINK1-dependent manner on the mitochondria (9, 21). Parkin ubiquitinates numerous proteins of the OMM (26, 27), and thereby recruits autophagy-related proteins to the damaged mitochondrion for autophagosome assembly (28-30).How PINK1 recruits and activa...