title: Hyaluronan synthase control of synthesis rate and hyaluronan product size are independent functions differentially affected by mutations in a conserved tandem B-X7-B motif.
abstract: Hyaluronan synthases (HAS) normally make large (>MDa) hyaluronan (HA) products. Smaller HA fragments (e.g. 100-400 kDa) produced in vivo are associated with inflammation and cell signaling by HA receptors that bind small, but not large, HA. Although HA fragments can arise from breakdown by hyaluronidases, HAS might also be regulated directly to synthesize small HA. Here we examined the Streptococcus equisimilis HAS (SeHAS) C-terminus, which contains a tandem B-X7-B motif (K398-X7-R406-X7-K414), by testing the effects of 27 site-specific scanning mutations and 7 C-terminal truncations on HA synthesis activity and weight-average mass. Although HAS enzymes cannot be HA-binding proteins, these motifs are highly conserved within the Class I HAS family. Fifteen Arg406mutants made large MDa HA (86-110% wildtype size), with specific activities from 70% to 177% of wildtype. In contrast, 10 of 12 Lys398mutants made HA that was 8-14% of wildtype size (≤250-480 kDa), with specific activities from 14% to 64% of wildtype. Four nearly inactive (2% wildtype activity) C-terminal truncation mutants made MDa HA (56-71% wildtype). The results confirm earlier findings with Cys-mutants [Weigel PH, Baggenstoss BA. 2012. Hyaluronan synthase polymerizing activity and control of product size are discrete enzyme functions that can be uncoupled by mutagenesis of conserved cysteines. Glycobiology 22:1302-1310] that HAS uses two independent activities to control HA size and HA synthesis rate; these are two separate functions. We conclude that HAS regulatory modifications that alter tandem B-X7-B motif conformation could mimic these mutagenesis-induced effects, allowing HAS in vivo to make small HA directly. The results also support a model in which the tandem-motif region is part of the intra-HAS pore and interacts directly with HA.
authors: Department of Biochemistry & Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors: Bruce A
authors: BA
authors: Baggenstoss
authors: Department of Biochemistry & Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors: Edward N
authors: EN
authors: Harris
authors: Department of Biochemistry & Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors: Jennifer L
authors: JL
authors: Washburn
authors: Department of Biochemistry & Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors: Andria P
authors: AP
authors: Medina
authors: Department of Biochemistry & Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors: Long
authors: L
authors: Nguyen
authors: Department of Biochemistry & Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA paul-weigel@ouhsc.edu.
authors: Paul H
authors: PH
authors: Weigel
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics*; D000595:Amino Acid Sequence / Q000235:genetics; D018960:Hyaluronan Receptors / Q000235:genetics / Q000378:metabolism; D000076002:Hyaluronan Synthases / Q000737:chemistry / Q000235:genetics*; D006820:Hyaluronic Acid / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D007249:Inflammation / Q000235:genetics*; D009154:Mutation; D011485:Protein Binding; D013291:Streptococcus / Q000201:enzymology
chemical_list: D018960:Hyaluronan Receptors; D006820:Hyaluronic Acid; D000076002:Hyaluronan Synthases
keywords: enzyme function; hyaluronan binding; hyaluronan biosynthesis; hyaluronan length; regulation