Conformational activation and inhibition of von Willebrand factor by targeting its autoinhibitory module.

ABSTRACT: Activation of von Willebrand factor (VWF) is a tightly controlled process governed primarily by local elements around its A1 domain. Recent studies suggest that the O-glycosylated sequences flanking the A1 domain constitute a discontinuous and force-sensitive autoinhibitory module (AIM), although its extent and conformation remains controversial. Here, we used a targeted screening strategy to identify 2 groups of nanobodies. One group, represented by clone 6D12, is conformation insensitive and binds the N-terminal AIM (NAIM) sequence that is distal from A1; 6D12 activates human VWF and induces aggregation of platelet-rich plasma at submicromolar concentrations. The other group, represented by clones Nd4 and Nd6, is conformation sensitive and targets the C-terminal AIM (CAIM). Nd4 and Nd6 inhibit ristocetin-induced platelet aggregation and reduce VWF-mediated platelet adhesion under flow. A crystal structure of Nd6 in complex with AIM-A1 shows a novel conformation of both CAIM and NAIM that are primed to interact, providing a model of steric hindrance stabilized by the AIM as the mechanism for regulating GPIbα binding to VWF. Hydrogen-deuterium exchange mass spectrometry analysis shows that binding of 6D12 induces the exposure of the GPIbα-binding site in the A1 domain, but binding of inhibitory nanobodies reduces it. Overall, these results suggest that the distal portion of NAIM is involved in specific interactions with CAIM, and binding of nanobodies to the AIM could either disrupt its conformation to activate VWF or stabilize its conformation to upkeep VWF autoinhibition. These reported nanobodies could facilitate future studies of VWF functions and related pathologies.

Design, Synthesis, and Evaluation of New 1H-Benzo[d]imidazole Based PqsR Inhibitors as Adjuvant Therapy for Pseudomonas aeruginosa Infections.

Pseudomonas aeruginosa is one of the top priority pathogens that requires immediate attention according to the World Health Organisation (WHO). Due to the alarming shortage of novel antimicrobials, targeting quorum sensing (QS), a bacterial cell to cell signaling system controlling virulence, has emerged as a promising approach as an antibiotic adjuvant therapy. Interference with the pqs system, one of three QS systems in P. aeruginosa, results in reduction of bacterial virulence gene expression and biofilm maturation. Herein, we report a hit to lead process to fine-tune the potency of our previously reported inhibitor 1 (IC50 3.2 µM in P. aeruginosa PAO1-L), which led to the discovery of 2-(4-(3-((6-chloro-1-isopropyl-1H-benzo[d]imidazol-2-yl)amino)-2-hydroxypropoxy)phenyl)acetonitrile (6f) as a potent PqsR antagonist. Compound 6f inhibited the PqsR-controlled PpqsA-lux transcriptional reporter fusion in P. aeruginosa at low submicromolar concentrations. Moreover, 6f showed improved efficacy against P. aeruginosa CF isolates with significant inhibition of pyocyanin, 2-alkyl-4(1H)-quinolones production.

Inherited ADAMTS13 mutations associated with Thrombotic Thrombocytopenic Purpura: a short review and update.

ADAMTS13 is a plasma metalloprotease with the primary function of cleaving VWF to maintain hemostasis. Circulating ADAMTS13 is in the closed conformation until blood vessel injury triggers a VWF-dependant activation to the open active form of the protein. ADAMTS13 is a multi-domain protein with the domains broadly functioning to interact and cleave VWF or maintain global latency of ADAMTS13. Thrombotic Thrombocytopenic Purpura is a disease characterized by excessive thrombi formation in the microvasculature, diagnosis is made when ADAMTS13 activity is <10%. In the hereditary form, a variety of mutations are found throughout all domains of ADAMTS13, examples are given alongside details of each domain in this article. ADAMTS13 mutations can inhibit the binding and cleavage of VWF directly or indirectly through reduced secretion, leading to increased size of VWF multimers and platelet recruitment. Molecular characterization of ADAMTS13 may provide insight into the mechanisms of TTP to aid in both scientific and clinical research.