Glycosylation of at least one residue in RBD-containing fragments is required for expression. A) Expression pattern of two mutants on S319–518 in which both the glycosylation sites at N330 and N357 have been mutated either to alanine or to glutamine. No expression is seen when both the sites have been mutated indicating that glycosylation of at least one of the sites is important. In the last lane, purified S317–518 protein has been loaded as a control. B) Cell binding results of the same mutants.