Human T-lymphotropic virus type 1 non-structural proteins: Requirements for latent infection

Portrait of the Intrinsically Disordered Side of the HTLV-1 Proteome

Intrinsically disordered proteins (IDPs) lack an ordered 3D structure. These proteins contain one or more intrinsically disordered protein regions (IDPRs). IDPRs interact promiscuously with other proteins, which leads to their structural transition from a disordered to an ordered state. Such interaction-prone regions of IDPs are known as molecular recognition features. Recent studies suggest that IDPs provide structural plasticity and functional diversity to viral proteins that are involved in rapid replication and immune evasion within the host cells. In the present study, we evaluated the prevalence of IDPs and IDPRs in human T lymphotropic virus type 1 (HTLV-1) proteome. We also investigated the presence of MoRF regions in the structural and nonstructural proteins of HTLV-1. We found abundant IDPRs in HTLV-1 bZIP factor, p30, Rex, and structural nucleocapsid p15 proteins, which are involved in diverse functions such as virus proliferation, mRNA export, and genomic RNA binding. Our study analyzed the HTLV-1 proteome with the perspective of intrinsic disorder identification. We propose that the intrinsic disorder analysis of HTLV-1 proteins may form the basis for the development of protein disorder-based drugs.

Non-Structural Proteins from Human T-cell Leukemia Virus Type 1 in Cellular Membranes-Mechanisms for Viral Survivability and Proliferation

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of illnesses, such as adult T-cell leukemia/lymphoma, myelopathy/tropical spastic paraparesis (a neurodegenerative disorder), and other diseases. Therefore, HTLV-1 infection is a serious public health concern. Currently, diseases caused by HTLV-1 cannot be prevented or cured. Hence, there is a pressing need to comprehensively understand the mechanisms of HTLV-1 infection and intervention in host cell physiology. HTLV-1-encoded non-structural proteins that reside and function in the cellular membranes are of particular interest, because they alter cellular components, signaling pathways, and transcriptional mechanisms. Summarized herein is the current knowledge about the functions of the membrane-associated p8^I, p12^I, and p13^II regulatory non-structural proteins. p12^I resides in endomembranes and interacts with host proteins on the pathways of signal transduction, thus preventing immune responses to the virus. p8^I is a proteolytic product of p12^I residing in the plasma membrane, where it contributes to T-cell deactivation and participates in cellular conduits, enhancing virus transmission. p13^II associates with the inner mitochondrial membrane, where it is proposed to function as a potassium channel. Potassium influx through p13^II in the matrix causes membrane depolarization and triggers processes that lead to either T-cell activation or cell death through apoptosis.

Human T-lymphotropic virus type 1 non-structural proteins: Requirements for latent infection

It has been more than 30 years since the discovery of human T-lymphotropic virus type 1 (HTLV-1), the first human retrovirus identified. Human T-lymphotropic virus type 1 infects 15-20 million people worldwide causing two major diseases: adult T-cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis. Human T-lymphotropic virus type 1 establishes several decades of latent infection, during which viral-host interaction determines disease segregation. This review highlights non-structural proteins that are encoded on the viral genome and manage latent infection. Latent infection is a key in HTLV pathology, so that effective inhibition of these proteins might lead to successful disease management.