Studies on the primary structure of the influenza virus hemagglutinin.

The amino-terminal sequence and composition of the subunits of the hemagglutinin (HA) of influenza virus has been determined. The hemagglutinin has been isolated by two techniques. (1) as the intact hemagglutinin after disruption of the virus in sodium dodecyl sulfate, giving 2 subunits of 58,000 daltons (HA1) and 26,000 daltons (HA2), and (2) after treatment of the virus with bromelain, giving 2 subunits of 58,000 daltons (BHA1) and 21,000 daltons (BHA2). In both preparations these subunits are linked by disulfide bonds. The aminoterminal sequences of HA1 and BHA1, and HA2 and BHA2 are the same. The composition of the 50 residue peptide associated with the membrane, which is removed from the C-terminus of HA2 by bromelain, is deduced and shown to be hydrophobic and contain 50% of the serine residues of HA2. The biosynthetic precursor of the hemagglutinin has been purified from the membranes of abortively infected chick fibroblasts and shown to have the same amino terminus as HA1. Thus the order of biosynthesis is NH2-HA1-HA2-COOH. The amino-terminal sequence of BHA2--at the cleavage site of the precursor--is shown to be a palindrome: NH2-Gly-Leu-Phe-Gly-Ala-Ile-Ala-Gly-Phe-Ile-. This sequence is conserved in representative viruses from each of the major pandemics. A region of homologous sequence is described between the hemagglutinins of influenza type A and B viruses.