Autoinhibition of suicidal capsid protease from O'nyong'nyong virus

Alphaviruses pose a significant threat to public health. Capsid protein encoded in the alphaviral genomes constitutes an interesting therapy target, as it also serves as a protease (CP). Remarkably, it undergoes autoproteolysis, leading to the generation of the C-terminal tryptophan that localizes to the active pocket, deactivating the enzyme. Lack of activity hampers the viral replication cycle, as the virus is not capable of producing the infectious progeny. We investigated the structure and function of the CP encoded in the genome of O'nyong'nyong virus (ONNV), which has instigated outbreaks in Africa. Our research provides a high-resolution crystal structure of the ONNV CP in its active state and evaluates the enzyme's activity. Furthermore, we demonstrated a dose-dependent reduction in ONNV CP proteolytic activity when exposed to indole, suggesting that tryptophan analogs may be a promising basis for developing small molecule inhibitors. It's noteworthy that the capsid protease plays an essential role in virus assembly, binding viral glycoproteins through its glycoprotein-binding hydrophobic pocket. We showed that non-aromatic cyclic compounds like dioxane disrupt this vital interaction. Our findings provide deeper insights into ONNV's biology, and we believe they will prove instrumental in guiding the development of antiviral strategies against arthritogenic alphaviruses.

Human mAbs Broadly Protect against Arthritogenic Alphaviruses by Recognizing Conserved Elements of the Mxra8 Receptor-Binding Site

Mosquito inoculation of humans with arthritogenic alphaviruses results in a febrile syndrome characterized by debilitating musculoskeletal pain and arthritis. Despite an expanding global disease burden, no approved therapies or licensed vaccines exist. Here, we describe human monoclonal antibodies (mAbs) that bind to and neutralize multiple distantly related alphaviruses. These mAbs compete for an antigenic site and prevent attachment to the recently discovered Mxra8 alphavirus receptor. Three cryoelectron microscopy structures of Fab in complex with Ross River (RRV), Mayaro, or chikungunya viruses reveal a conserved footprint of the broadly neutralizing mAb RRV-12 in a region of the E2 glycoprotein B domain. This mAb neutralizes virus in vitro by preventing virus entry and spread and is protective in vivo in mouse models. Thus, the RRV-12 mAb and its defined epitope have potential as a therapeutic agent or target of vaccine design against multiple emerging arthritogenic alphavirus infections.

Arthritogenic Alphaviruses: A Worldwide Emerging Threat?

Arthritogenic alphaviruses are responsible for a dengue-like syndrome associated with severe debilitating polyarthralgia that can persist for months or years and impact life quality. Chikungunya virus is the most well-known member of this family since it was responsible for two worldwide epidemics with millions of cases in the last 15 years. However, other arthritogenic alphaviruses that are as of yet restrained to specific territories are the cause of neglected tropical diseases: O'nyong'nyong virus in Sub-Saharan Africa, Mayaro virus in Latin America, and Ross River virus in Australia and the Pacific island countries and territories. This review evaluates their emerging potential in light of the current knowledge for each of them and in comparison to chikungunya virus.