Neuroendocrine secretory granules. Binds keratan sulfate chains. May be proteolytically processed to give rise to a number of active peptides. This protein is produced by a bicistronic gene which also produces the ALEX protein from an overlapping reading frame. The GNAS locus is imprinted in a complex manner, giving rise to distinct paternally, maternally and biallelically expressed proteins. The XLas isoforms are paternally derived, the Gnas isoforms are biallelically derived and the Nesp55 isoforms are maternally derived. Shares no sequence similarity with other isoforms (except isoform Nesp55-2) due to a novel first exon containing the entire reading frame spliced to shared exon 2 so that exons 2-13 make up the 3'-UTR. Shares no sequence similarity with other isoforms (except isoform Nesp55-1) due to a novel first exon containing the entire reading frame spliced to shared exon 2 so that exons 2-13 make up the 3'-UTR. Belongs to the NESP55 family.