The Amino Acid Sequence of a Hong Kong Influenza Haemagglutinin Light (HA2) Chain

The amino acid sequence of the Hong Kong haemagglutinin light chain (HA2; 222 residues) is nearly complete, lacking only the definition of a highly aggregated region near the carboxyl terminal end of the chain. This unsequenced area of approx. 25 residues occurs near the carboxyl terminal end of cyanogen bromide peptide CN-1, whose structure determination is discussed in this paper. All ½-cystine residues present in HA2 occur in CN-1, as a proximal cluster involving residues 137, 144 and 148, and as a distal cluster involving four other ½-cystine residues near the carboxyl terminus of HA2, three of which have been placed within peptides. The single glycosylated asparagine in HA2 also occurs in CN-1; the carbohydrate moiety is complex. The structure of HA2 is discussed in terms of its properties, and compared with published data from haemagglutinins from other influenza strains.