Schistosomiasis Research Group

As well as being used for protein identification, mass spectrometry can also help to characterise the glycan moieties of glycoproteins and glycolipids which can function as antigenic epitopes, provoking antibody production.  Given the potent response that primates make to such glycans, we have questioned whether this reactivity represents a smokescreen rather than a component of protective immunity (Eberl, et al. 2001).  This is especially true of the parasite egg, which seems to advertise its presence by releasing proinflammatory secretions to provoke a response essential for its transit through tissues to the gut lumen.  The glycan residues must first be released from the parent protein(s) by PNGase F and PNGase A treatment for N glycans and reductive elimination for the O glycans, prior to mass spectrometry.

Empirical structures can be predicted from the masses obtained but structure assignments then need to be confirmed by further rounds of exo-glycosidase digestions, and tandem MS.  Our collaboration with Professor Anne Dell of Imperial College, London to characterise the glycoproteins released by cercariae and mature eggs, has revealed a rich mixture of both N and O glycans.  Moreover, the majority of cercarial N glycans appear to be shared with eggs, but the latter contain many glycans structures not present in the cercarial secretions.  The fact that immunisation with eggs fails to elicit protection is further evidence that the cross-reactive N glycans are a smokescreen.  In the future we hope to assign definitive structures and biological functions to the various glycans we have found.

MALDI mass spectrum of glycans released by PNGase F from the cercarial acetabular gland secretions, showing putative structure assignments.