Structure of the haemagglutinin membrane glycoprotein of influenza virus at 3 Å resolution

Abstract
The haemagglutinin glycoprotein of influenza virus is a trimer comprising two structurally distinct regions: a triple-stranded coiled-coil of α-helices extends 76 Å from the membrane and a globular region of antiparallel β-sheet, which contains the receptor binding site and the variable antigenic determinants, is positioned on top of this stem. Each subunit has an unusual loop-like topology, starting at the membrane, extending 135 Å distally and folding back to enter the membrane.