Structural investigations of glycosaminoglycan biosynthetic enzymes
||Structural investigations of glycosaminoglycan biosynthetic enzymes|
||Emil Tykesson <email@example.com>|
||2022-05-24 – 2022-12-01|
The extracellular matrix (ECM) is a network of proteins and glycans that surrounds cells. Proteoglycans (PGs) are integral components of the ECM and consist of a core protein with one or more covalently attached glycosaminoglycan (GAG) chains, which are linear polysaccharides consisting of repeating disaccharide structures. A common GAG is chondroitin/dermatan sulfate (CS/DS). In CS/DS, the disaccharide repeating unit consists of a uronic acid, that is glucuronic acid (GlcA) or iduronic acid (IdoA), linked to an N-acetylated galactosamine (GalNAc). For IdoA-containing CS/DS chains, the first chain modification step is epimerization of GlcA into IdoA. Our group has identified and cloned the two human CS/DS epimerases, dermatan sulfate epimerase 1 and -2 (DSE and DSEL). DSE is, by far, the most widely expressed of the two, and can be found throughout the body, except in serum. Subsequent sulfation by dermatan 4-O-sulfotransferase 1 (D4ST1), which transfers a sulfate to position four of GalNAc next to IdoA, is tightly coupled to epimerization. Consequently, the patterns of epimerization and sulfation are tightly coupled to specific GAG-protein interactions. Even though two GAG polymers can have almost identical disaccharide composition, the sequence of assembly is of uttermost importance for biological functions. One part of understanding the mechanism of DSE and D4ST1 is to study their structures. We have still not succeeded in crystallizing D4ST1 on its own; however, DSE has crystallized under several different conditions and we have recently published a 2.4 Å structure from DSE apo crystals collected at BioMAX at MAX IV. We have now want to make use of single particle three-dimensional (3D) electron microscopy (cryo-EM) as a tool to gain further structural insight into DSE, D4ST1 and potentially other GAG biosynthetic enzymes.