Length and Composition Analysis of the Cytoplasmic, Transmembrane and Stem Regions of Human Golgi Glycosyltransferases

A dataset of experimentally characterized, human Golgi GlyTs with type II membrane topology was created. Based on the experimentally observed acceptor substrate preferences, the GlyTs were classified into five functional categories: biosynthesis of blood group antigens, glycolipids, N-glycans, O-glycans and glycosaminoglycans. The cytoplasmic, transmembrane and stem (CTS) regions were predicted and their length and composition were analyzed. The stem region of GlyTs involved in the biosynthesis of glycolipids and blood group antigens appear to have a shorter stem region compared to those GlyTs which participate in the biosynthesis of N- and O-linked glycans and glycosaminoglycans. The stem regions of all the GlyTs, irrespective of the functional category to which they belong, were found to be rich in disorder- promoting amino acid residues. Thus, the stem region is largely devoid of any regular secondary structure thereby facilitating its tethering role. A higher frequency of occurrence of basic amino acids is observed towards the N-terminus of the transmembrane domain and this is suggested to be important for topogenesis of these enzymes.