Selective and transient association of Sendai virus HN glycoprotein with BiP

From 10-min [35S]methionine pulse-labeled Sendai virus-infected BHK cells, an anti-BiP monoclonal antibody precipitated, along with the BiP protein, the hemagglutinin-neuraminidase protein (SV-HN) fivefold better than the fusion protein (SV-Fo). A minimal estimate of 30% of the newly made HN was complexed to BiP. The majority of the HN in the complex was endo-H sensitive and the molar ratio of BiP:HN was estimated to be 1:2. With time, HN dissociated from BiP, and the rate of dissociation was found to be inversely proportional to the rate at which HN acquired its native structure. It is proposed that association with BiP followed by slow release (i) is responsible for the HN slow maturation and (ii) represents a normal step in its maturation pathway.