The N-terminal heptad repeat region of reovirus cell attachment protein σ1 is responsible for σ1 oligomer stability and possesses intrinsic oligomerization function

The oligomerization domain of the reovirus cell attachment protein (σ1) was probed using the type 3 reovirus of synthesized in vitro. Trypsin cleaved the α1 protein (49K molecular weight) approximately in the middle and yielded a 26K N-terminal fragment and a 23K C-terminal fragment. Under conditions which allowed for the identification of intact σ1 in the oligomeric form (∼200K) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the N-terminal 26K fragment was found to exist as stable trimers (80K) and, to a less extent, as dimers (54K), whereas the C-terminal fragment remained in the monomeric form. A polypeptide (161 amino acids) containing the N-terminal heptad repeat region synthesized in vitro was capable of forming stable dimers and trimers. Using various criteria, we demonstrated that the stability of the intact σ1 oligomer is conferred mainly by the N-terminal heptad repeat region. Our results are summarized in a model in which individual heptad repeats are held together in a three-stranded α-helical coiled-coil structure via both hydrophobic and electrostatic interactions.