Crystal structure and cap binding analysis of the methyltransferase of langat virus.

Tick-borne encephalitis virus (TBEV) is a major dangerous human pathogen, as TBEV infection can cause serious illness that can lead to irreversible neurological sequelae and even death. Langat virus (LGTV), a member of the tick-borne encephalitis virus (TBEV) serogroup, belongs to the family Flaviviridae, genus Flavivirus. Its nonstructural protein 5 (NS5) protein contains a methyltransferase (MTase) domain that can methylate RNA cap structures, which is critical for viral replication. We determined the structure of LGTV NS5 methyltransferase bound to S-adenosyl-L-homocysteine (SAH) at a 1.70 Å resolution. Sequence analysis and structural comparison of homologous MTases suggests that folds and structures are closely conserved throughout Flavivirus species and play important roles. This study provides the key structural information on LGTV MTase and the foundation for research on antiviral drugs targeting LGTV MTase.