Structural insights into translocation and tailored synthesis of hyaluronan
Ireneusz Górniak, Zachery Stephens, Satchal K. Erramilli, Tomasz Gawda, Anthony A. Kossiakoff, Jochen Zimmer
Abstract
Hyaluronan (HA) is an essential component of the vertebrate extracellular matrix. It is a heteropolysaccharide of N-acetylglucosamine (GlcNAc) and glucuronic acid (GlcA) reaching several megadaltons in healthy tissues. HA is synthesized and translocated in a coupled reaction by HA synthase (HAS). Here, structural snapshots of HAS provide insights into HA biosynthesis, from substrate recognition to HA elongation and translocation. We monitor the extension of a GlcNAc primer with GlcA, reveal the coordination of the uridine diphosphate product by a conserved gating loop and capture the opening of a translocation channel to coordinate a translocating HA polymer. Furthermore, we identify channel-lining residues that modulate HA product lengths. Integrating structural and biochemical analyses suggests an avenue for polysaccharide engineering based on finely tuned enzymatic activity and HA coordination.