Sialic acid binding activity of transmissible gastroenteritis coronavirus affects sedimentation behavior of virions and solubilized glycoproteins

The sedimentation behavior of transmissible gastroenteritis coronavirus (TG EV) was analyzed. Upon sucrose gradient centrifugation, the major virus ban d was found at a density of 1.20 to 1.22 g/cm(3), This high density was obs erved only when TGEV with a functional sialic acid binding activity was ana lyzed. Mutants of TGEV that lacked sialic acid binding activity due to a po int mutation in the sialic acid binding site of the S protein were mainly r ecovered at a lower-density position on the sucrose gradient (1.18 to 1.19 g/cm(3)). Neuraminidase treatment of purified virions resulted in a shift o f the sedimentation value from the higher to the lower density. These resul ts suggest that binding of sialoglycoproteins to the virion surface is resp onsible for the sedimentation behavior of TGEV. When purified virions were treated with octylglucoside to solubilize viral glycoproteins, ultracentrif ugation resulted in sedimentation of the S protein of TGEV. However, when n euraminidase-treated virions or mutants with a defective sialic acid bindin g activity were analyzed, the S protein remained in the supernatant rather than in the pellet fraction. These results indicate that the interaction of the surface protein S with sialoglycoconjugates is maintained after solubi lization of this viral glycoprotein by detergent treatment.