Jos Jansen

136 Chapter 6 Glycomics Usually, a severe phenotype in infancy triggers genetic investigations for inborn errors of metabolism, including congenital glycosylation disorders. This has always been dependent on isoelectric focusing and thus the glycosylation pattern of transferrin. The success of this method is exemplified by the amount of discovered CDG. As explained in the introduction, QTOF-MS of the intact transferrin protein broadened the spectrum of glycosylation disorders, not dependent on the number of sialic acids. A disadvantage of this method is tissue and/or protein specificity. New methods are being developed to analyse the glycopeptides and will provide new valuable insights in these matters. Additionally, experimental designs identified new proteins associated with abnormal glycosylation, such as TMEM59 and TMEM115. (10, 11) These genes should be a target for screening in patients with abnormal glycosylation. 2. Can we correlate the phenotype of CCDC115 and TMEM199 deficiency to more common hepatic diseases? As a consequence of our search strategy, yeast homology, little is known on the function of both proteins in human. In chapter 2 and 3 we show that dysfunction leads to abnormal Golgi-located glycosylation, indicating a detrimental effect on the Golgi. The phenotype, with hepatic steatosis and mild copper accumulation, provides addition (indirect) evidence for a role in hepatic lipid metabolism and copper metabolism. In chapter 4 we reviewed V-ATPase assembly factor functions and explored their effects on hepatic lipid metabolism and correlated CCDC115 and TMEM199 deficiency with NAFLD. The conclusion was that protein trafficking plays a significant role in hepatic lipidmetabolism and we hypothesize a possible role for abnormal COPI trafficking as a common etiology. Differences between yeast and human Chapters 2 and 3 show that CCDC115 and TMEM199 are highly conserved within the eukaryotes and that homology detection was reciprocal with Vma22p and Vph2p, indicative for orthology. Most research on their function was conducted in S. cerevisiae and reviewed in chapter 4. After our publications came out, one paper was published on TMEM199 and CCDC115 in HeLa cells.(12) In this paper, reciprocal immunoprecipitation of TMEM199 and CCDC115 was proven.