Glycosylation of the capsid proteins of cowpea mosaic virus: a reinvestigation shows the absence of sugar residues

The previously reported (Partridge et al., Nature 247, 391-392, 1974) glycosylation of the capsid proteins of cowpea mosaic virus (CPMV) has been reinvestigated. In initial studies, a preparation of purified CPMV particles was hydrolysed with HCl and amino acids and sugars were derivatized with o-phthalaldehyde (OPA). No glucosamine or galactosamine, amino sugars previously reported to occur in significant quantities in CPMV capsids, could be detected by reverse-phase high-performance liquid chromatography (RP-HPLC) of the derivatized hydrolysates. A complete analysis of all sugars potentially present was carried out by hydrolysing a sample of purified CPMV capsid proteins and derivatizing the sugars with 1-phenyl-3-methyl-5-pyrazolone. RP-HPLC analysis demonstrated that the capsids do not contain significant quantities of any sugar. The results show that, contrary to the previous report, the coat proteins of CPMV are not glycosylated.