THE CARBOXY-TERMINAL-18 AMINO-ACIDS OF THE MEASLES-VIRUS HEMAGGLUTININ ARE ESSENTIAL FOR ITS BIOLOGICAL FUNCTION

The hemagglutinin (HA) glycoprotein encoded by measles virus (MV) is a type II integral membrane protein that is expressed at the infected cell surface. Genes encoding wild-type MV HA as well as two mutant HA proteins shortened at their carboxy-termini by either 18 (HA Delta 18) or 223 (HA Delta 223) amino acids were constructed and studied in a transient expression system in COS cells. Under nonreducing conditions, assembly of HA Delta 18 into homodimers was diminished while HA Delta 223 remained in a monomeric form. Hemadsorption assays revealed that neither mutant was functional at the cell surface. These studies show that the carboxy-terminal ectodomain of the HA protein is essential to its proper folding and assembly into homodimers while its carboxy-terminal 18 amino acids are essential for the hemadsorption (receptor-binding) function of the protein. (C) 1995 Academic Press, Inc.