The disulphide bonds of a Hong Kong influenza virus hemagglutinin

Abstract

1. Introduction The major antigen of influenza virus is a hemag- glutinin [ 1,2] which attaches the virus to the cell surface receptors on infection [3]. This hemagglu- tinin consists of a heavy chain (HAl, mol. wt 47 000 [4]) and a light chain (HA2, mol. wt 30 000 [4]), which are linked by disulphide bon.ds [S]. Three hemagglutiniri molecules join by hydrophobic bond- ing to form a trimeric spike [6,7], protruding from the viral membrane [S]. These features and functions imply a high level of structural organisation, in which the disulphide bonds would be expected to play an important role, espe- cially since we have found 9 Cyss in HA1 [9] and 7 Cyss in HA2 [lo]. This letter reports the isolation and pairing of disulphide peptides in influenza hemagglutinin. We show by referring to published sequence data [9,1 I] that 3 S-S bonds link the 2 chains, and that HA1 contains 3 intrachain S-S bonds. The other 4 Cyss residues in the light chain occur in the hydrophobic tail [IO] and can only be paired amongst themselves. 2. Materials and methods Viral hemagglutinin (HA) was prepared as in [9]. HA was digested with thermolysin for 24 h at 37°C in 0.1 M N-ethylmorpholine acetate (pH 8.0) at a 100: 1 substrate to enzyme level. Ammo acids were analysed on a phthalaldehyde- based analyser; 100-200 pmol samples were hydro- lysed at 110°C in 20 /_d constant boiling HCl. Diagonal peptide maps were prepared at pH 6.5 essentially as in [ 121. The neutral spots were further