Glycan-shielded homodimer structure and dynamical features of the canine distemper virus hemagglutinin relevant for viral entry and efficient vaccination

Abstract

Canine distemper virus (CDV) belongs to morbillivirus, including measles virus (MeV), which causes serious immunological and neurological disorders in carnivores, but their vaccines are highly effective. The attachment glycoprotein hemagglutinin (CDV-H) at the CDV surface utilizes signaling lymphocyte activation molecule (SLAM) and Nectin-4 as entry receptors. Although fusion models have been proposed, the molecular mechanism of morbillivirus fusion entry is poorly understood. Here, we determined the crystal structure of the globular head domain of CDV-H vaccine strain at 3.2 Å resolution, revealing that CDV-H exhibits a highly tilted homodimeric form with a six-bladed β-propeller fold. While the predicted Nectin-4 binding site is well-conserved with that of MeV-H, that of SLAM is similar but partially different, which contributes to host specificity. Five N-linked sugars covered a broad area of the CDV-H surface to expose receptor binding sites only, supporting the effective production of neutralizing antibodies. These features are common to MeV-H, although the glycosylation sites are completely different. Furthermore, real-time observation using high-speed atomic force microscopy revealed highly mobile features of the CDV-H dimeric head. These results suggest that sugar-shielded tilted-homodimeric structure and dynamic changes are common characteristics of morbilliviruses and ensure effective fusion entry and vaccination.