Heterologous production, purification and characterization of enzymatically active Sindbis virus nonstructural protein nsP1

► We have purified enzymatically active alphavirus capping enzyme, nsP1. ► Purified Sindbis virus (SINV) nsP1 possess the methyltransferase (MTase) and guanylyltransferase (GTase) activities. ► This indicates that alphavirus nsP1 does not require membrane association for its enzymatic function. ► SINV nsP1 GTase activity is metal-ion dependent, whereas MTase does not require a metal ion. ► CD analysis shows that the nsP1 has a mixed α/β structure consisting of 32.8% α-helix, 19.5% β-sheet, 19% β-turn and 32.5% random coil.