Disulphide bonds of haemagglutinin of Asian influenza virus.

The complete amino acid sequences of the haemagglutinins (HAs) of one strain of each of the Hav1 and H2 subtypes and of three strains of the H3 subtype of influenza virus have been established. A large external fragment (BHA) of HA can be released from virus particles using the protease bromelain that cleaves the protein close to its carboxyl terminus, which is inserted in the virus membrane (see Fig 1). Here we show that a single disulphide bond joins the two component polypeptide chains BHA1 and BHA2 and establish the location of five intrachain disulphides. These disulphide bonds have been located in the three-dimensional structure of HA which is known to 3 A resolution.