The high mannose glycans from bovine ribonuclease B isomer characterization by ion trap MS

Thirteen high mannose isomers have been structurally characterized within three glycomers, Man₅GlcNAc₂, Man₇GlcNAc₂, and Man₈GlcNAc₂ released from bovine ribonuclease B, six previously unreported. The study was carried out with a single ion trap instrument involving no chromatography. Three previously characterized isomers from Man₇ and Man₈ (three each) have been identified plus one unreported Man₇ isomer. Incomplete α-glucosidase activity on the Man₆ and Man₇ glycoproteins appears to account for two additional isomeric structures. The preeminence of ion traps for detail analysis was further demonstrated by resolving three new isomers within the Man₅ glycomer summing to the six previously unreported structures in this glycoprotein. All reported structures represent a distribution of Golgi processing remnants that fall within the Man₉GlcNAc₂ footprint. Topologies were defined by ion compositions along a disassembly pathway while linkage and branching were aided by spectral identity in a small oligomer fragment library. Isomers from this glycoprotein appear to represent a distribution of Golgi processing remnants, and an alphanumeric classification scheme has been devised to identify all products. Although numerous analytical strategies have been introduced to identify selected components of structure, it has been the continued focus of this and previous reports to only build upon protocols that can be integrated into a high throughput strategy consistent with automation. Duplication of these and results from comparable standards could bring an important analytical focus to carbohydrate sequencing that is greatly lacking.