Poster Presentation 24th Annual Lorne Proteomics Symposium 2019

The sweet connections in neurotransmission – investigating sialylated glycosylation in the active zone of nerve terminals (#69)

Inga Boll 1 , Pia Jensen 1 , Martin R Larsen 1
  1. University of Southern Denmark, Odense, Denmark

Even though the importance of sialic acids and sialylated glycoproteins for brain development was observed about three decades ago, most global studies regarding the cell biology of the neuron focused on genomics or proteomics, but barely touched upon PTMomics and especially not on glycoproteomics. Examining the signalling of nerve terminals during synaptic transmission, most studies investigated the alteration of phosphorylation, because it is known to be fast and reversible. Nevertheless, glycan structures can be even more versatile than other PTMs due to their different isomeric monosaccharides, being combined by different linkages and branching. Our study applying sialylated glycopeptide enrichment and MS-based quantitative proteomics clearly shows that the role of sialylated glycoproteins in neuronal signalling upon depolarization has been underestimated.
By using isolated nerve terminals (synaptosomes) from rat brains and subsequent depolarization with KCl, the modulation of sialylated glycosylation was determined by using state-of-the-art methods for enrichment of sialylated glycopeptides combined with quantitative proteomics. Mapping the alterations after 5 seconds of depolarization led to the identification of 2419 unique sialylated formerly N-linked glycopeptides whereof 158 were upregulated and 328 downregulated with respect to sialylation. Furthermore, the enrichment of an active zone-like fraction revealed changes at the site of neurotransmitter release in detail. In this fraction, important synaptic proteins such as calcium, potassium and sodium channels, glutamate receptors, ATPases, sodium and potassium transporters as well as extracellular matrix, cell migration and adhesion proteins were regulated, supporting the importance of sialic acids in the signalling taking place in nerve terminals. Especially for ion channels and transporters, the addition or removal of sialic acids seemed to be dynamic suggesting that the negative charge modulates structure and function of these proteins. This would provide a hitherto unknown level of regulation of neuronal signalling.