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.

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 Arg406 mutants made large MDa HA (86-110% wildtype size), with specific activities from 70% to 177% of wildtype. In contrast, 10 of 12 Lys398 mutants 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.

Hyaluronan synthase mediates dye translocation across liposomal membranes.

BACKGROUND: Hyaluronan (HA) is made at the plasma membrane and secreted into the extracellular medium or matrix by phospolipid-dependent hyaluronan synthase (HAS), which is active as a monomer. Since the mechanism by which HA is translocated across membranes is still unresolved, we assessed the presence of an intraprotein pore within HAS by adding purified Streptococcus equisimilis HAS (SeHAS) to liposomes preloaded with the fluorophore Cascade Blue (CB). RESULTS: CB translocation (efflux) was not observed with mock-purified material from empty vector control E. coli membranes, but was induced by SeHAS, purified from membranes, in a time- and dose-dependent manner. CB efflux was eliminated or greatly reduced when purified SeHAS was first treated under conditions that inhibit enzyme activity: heating, oxidization or cysteine modification with N-ethylmaleimide. Reduced CB efflux also occurred with SeHAS K48E or K48F mutants, in which alteration of K48 within membrane domain 2 causes decreased activity and HA product size. The above results used liposomes containing bovine cardiolipin (BCL). An earlier study testing many synthetic lipids found that the best activating lipid for SeHAS is tetraoleoyl cardiolipin (TO-CL) and that, in contrast, tetramyristoyl cardiolipin (TM-CL) is an inactivating lipid (Weigel et al, J. Biol. Chem. 281, 36542, 2006). Consistent with the effects of these CL species on SeHAS activity, CB efflux was more than 2-fold greater in liposomes made with TO-CL compared to TM-CL. CONCLUSIONS: The results indicate the presence of an intraprotein pore in HAS and support a model in which HA is translocated to the exterior by HAS itself.

Direct Oral Anticoagulants for Pulmonary Embolism: Importance of Anatomical Extent.

Pulmonary embolism (PE) studies used direct oral anticoagulants (DOACs) with or without initial heparin. We aimed to (1) evaluate if PE patients benefit from initial heparin; (2) describe patient characteristics in the DOAC studies; and (3) investigate whether the anatomical extent of PE correlates with N-terminal pro-brain natriuretic peptide (NT-proBNP) levels, cause of PE, and recurrence rate. Our methods were (1) an indirect meta-analysis comparing the recurrence risk in DOAC-treated patients with or without initial heparin to those patients given heparin/vitamin K antagonist (VKA). (2) To compare the PE studies, information was extracted on baseline characteristics including anatomical extent. (3) The Hokusai-VTE study was used to correlate anatomical extent of PE with NT-proBNP levels, causes of PE, and recurrent venous thromboembolism (VTE). The meta-analysis included 11,539 PE patients. The relative risk of recurrent VTE with DOACs versus heparin/VKAs was 0.8 (95% confidence interval [CI]: 0.6-1.1) with heparin lead-in and 1.1 (95% CI: 0.8-1.5) without heparin. In the DOAC studies, the proportion of patients with extensive PE varied from 24 to 47%. In Hokusai-VTE, NT-proBNP was elevated in 4% of patients with limited and in over 60% of patients with extensive disease. Cause of PE and anatomical extent were not related. Recurrence rates increased from 1.6% with limited to 3.2% with extensive disease in heparin/edoxaban-treated patients, and from 2.4 to 3.9% in heparin/warfarin recipients. In conclusion, indirect evidence suggests a heparin lead-in before DOACs may be advantageous in PE. Anatomical extent was related to elevated NT-proBNP and outcome, but not to PE cause.

Impact of age, comorbidity, and polypharmacy on the efficacy and safety of edoxaban for the treatment of venous thromboembolism: An analysis of the randomized, double-blind Hokusai-VTE trial.

BACKGROUND: Many patients with venous thromboembolism (VTE) are elderly, have multiple comorbidities and take several concomitant medications. Physicians may prefer warfarin over direct oral anticoagulants (DOACs) in such patients because comparative data are lacking. This analysis was designed to determine the effects of advanced age, comorbidities, and polypharmacy on the efficacy and safety of edoxaban and warfarin in patients with VTE. METHODS: Using data from the Hokusai-VTE study, we report rates of recurrent VTE and of clinically relevant bleeding by age category (<65, 65-75, and ≥75; <80 versus ≥80years), and by number of comorbidities (0, 1-2, >2) and concomitant medications (<3, 3-5, >5). Hazard ratios (HR) and corresponding 95% confidence intervals (CI) for edoxaban versus warfarin were determined and Kaplan-Meier methodology was used to construct time-to-event curves. At 3months, pre- and postdose levels of edoxaban were measured using mass spectrometry. For warfarin-treated patients, the time in therapeutic range was calculated. The study was approved by institutional review boards; informed consent was obtained. RESULTS: Recurrent VTE increased with advanced age, multiple comorbidities, and polypharmacy in warfarin-treated patients but not with edoxaban. Edoxaban was more effective than warfarin in patients ≥75years of age and in those with multiple comorbidities. In the 517 patients over 80years of age, recurrent VTE occurred in 2.8% given edoxaban and in 5.7% given warfarin (HR 0.51, 95% CI 0.21-1.24). Bleeding increased with age, comorbidity, and polypharmacy regardless of treatment, but the relative safety of edoxaban versus well-managed warfarin was maintained. Age, comorbidity, and polypharmacy did not impact edoxaban concentrations. CONCLUSIONS: These data suggest that a once-daily fixed dose of edoxaban is more effective and at least as safe as warfarin in high-risk VTE patients identified by older age, more comorbidities, and polypharmacy. CLINICAL TRIAL REGISTRATION: NCT00986154.

Clustered Conserved Cysteines in Hyaluronan Synthase Mediate Cooperative Activation by Mg2+ Ions and Severe Inhibitory Effects of Divalent Cations.

Hyaluronan synthase (HAS) uses UDP-GlcUA and UDP-GlcNAc to make hyaluronan (HA). Streptococcus equisimilis HAS (SeHAS) contains four conserved cysteines clustered near the membrane, and requires phospholipids and Mg2+ for activity. Activity of membrane-bound or purified enzyme displayed a sigmoidal saturation profile for Mg2+ with a Hill coefficient of 2. To assess if Cys residues are important for cooperativity we examined the Mg2+ dependence of mutants with various combinations of Cys-to-Ala mutations. All Cys-mutants lost the cooperative response to Mg2+. In the presence of Mg2+, other divalent cations inhibited SeHAS with different potencies (Cu2+~Zn2+ >Co2+ >Ni2+ >Mn2+ >Ba2+ Sr2+ Ca2+). Some divalent metal ions likely inhibit by displacement of Mg2+-UDP-Sugar complexes (e.g. Ca2+, Sr2+ and Ba2+ had apparent Ki values of 2-5 mM). In contrast, Zn2+ and Cu2+ inhibited more potently (apparent Ki ≤ 0.2 mM). Inhibition of Cys-null SeHAS by Cu2+, but not Zn2+, was greatly attenuated compared to wildtype. Double and triple Cys-mutants showed differing sensitivities to Zn2+ or Cu2+. Wildtype SeHAS allowed to make HA prior to exposure to Zn2+ or Cu2+ was protected from inhibition, indicating that access of metal ions to sensitive functional groups was hindered in processively acting HA•HAS complexes. We conclude that clustered Cys residues mediate cooperative interactions with Mg2+ and that transition metal ions inhibit SeHAS very potently by interacting with one or more of these -SH groups.