Summary
Factor VIII and factor V share a repetitive domain structure of A1-A2-B-A3-C1-C2.
To define the region(s) within the factor VIII heavy chain that result in inefficient
expression of the recombinant protein, we expressed a series of factor VIH/factor
V chimeras that contained heterologous sequences from the A1 and/or A2 domains. Substitution
of the factor VIIIA1 domain dramatically reduced secretion of factor V ~ 500-fold,
whereas substitution of the factor VIII A2 domain had minimal effect on secretion.
Conversely, substitution of the factor V A1 domain increased secretion of factor VIII
~3-fold, whereas substitution of the factor V A2 domain actually reduced secretion
~4-fold. Pulse chase experiments confirmed that reduced expression levels were due
to decreased secretion rather than instability of secreted protein. Smaller substitutions
did not further localize within the A1 domain the regions responsible for inefficient
secretion.
