The structure of the extracellular region of human hepsin reveals a serine protease domain and a novel scavenger receptor cysteine-rich (SRCR) domain

Hepsin is an integral membrane protein that may participate in cell growth and in maintaining proper cell morphology and is overexpressed in a number of primary tumors. We have determined the 1.75 A resolution structure of the extracellular component of human hepsin. This structure includes a 255-residue trypsin-like serine protease domain and a 109-residue region that forms a novel, poorly conserved, scavenger receptor cysteine-rich (SRCR) domain. The two domains are associated with each other through a single disulfide bond and an extensive network of noncovalent interactions. The structure suggests how the extracellular region of hepsin may be positioned with respect to the plasma membrane.     

Hapivirins and diprovirins: novel θ-defensin analogs with potent activity against influenza A virus

θ-Defensins are cyclic octadecapeptides found in nonhuman primates whose broad antiviral spectrum includes HIV-1, HSV-1, severe acute respiratory syndrome coronavirus, and influenza A virus (IAV). We previously reported that synthetic θ-defensins called retrocyclins can neutralize and aggregate various strains of IAV and increase IAV uptake by neutrophils. This study describes two families of peptides, hapivirins and diprovirins, whose design was inspired by retrocyclins. The goal was to develop smaller partially cyclic peptides that retain the antiviral activity of retrocyclins, while being easier to synthesize. The novel peptides also allowed for systemic substitution of key residues to evaluate the role of charge or hydrophobicity on antiviral activity. Seventy-two hapivirin or diprovirin peptides are described in this work, including several whose anti-IAV activity equals or exceeds that of normal α- or θ-defensins. Some of these also had strong antibacterial and antifungal activity. These new peptides were active against H3N2 and H1N1 strains of IAV. Structural features imparting strong antiviral activity were identified through iterative cycles of synthesis and testing. Our findings show the importance of hydrophobic residues for antiviral activity and show that pegylation, which often increases a peptide's serum t(1/2) in vivo, can increase the antiviral activity of DpVs. The new peptides acted at an early phase of viral infection, and, when combined with pulmonary surfactant protein D, their antiviral effects were additive. The peptides strongly increased neutrophil and macrophage uptake of IAV, while inhibiting monocyte cytokine generation. Development of modified θ-defensin analogs provides an approach for creating novel antiviral agents for IAV infections.     

Copper-catalyzed azide-alkyne cycloaddition (click chemistry)-based Detection of Global Pathogen-host AMPylation on Self-assembled Human Protein Microarrays

AMPylation (adenylylation) is a recently discovered mechanism employed by infectious bacteria to regulate host cell signaling. However, despite significant effort, only a few host targets have been identified, limiting our understanding of how these pathogens exploit this mechanism to control host cells. Accordingly, we developed a novel nonradioactive AMPylation screening platform using high-density cell-free protein microarrays displaying human proteins produced by human translational machinery. We screened 10,000 unique human proteins with Vibrio parahaemolyticus VopS and Histophilus somni IbpAFic2, and identified many new AMPylation substrates. Two of these, Rac2, and Rac3, were confirmed in vivo as bona fide substrates during infection with Vibrio parahaemolyticus. We also mapped the site of AMPylation of a non-GTPase substrate, LyGDI, to threonine 51, in a region regulated by Src kinase, and demonstrated that AMPylation prevented its phosphorylation by Src. Our results greatly expanded the repertoire of potential host substrates for bacterial AMPylators, determined their recognition motif, and revealed the first pathogen-host interaction AMPylation network. This approach can be extended to identify novel substrates of AMPylators with different domains or in different species and readily adapted for other post-translational modifications.Protein AMPylation (adenylylation) was recently discovered in bacteria-host interactions where virulence factors catalyze AMPylation using either a conserved Fic domain (e.g., VopS, Vibrio parahaemolyticus (V. para) and IbpA, Histophilus somni) or an adenylyl transferase domain (e.g., DrrA, Legionella pneumophila). These bacterial AMPylation enzymes, or AMPylators, are secreted into the host cells by bacterial secretion systems and transfer AMP from ATP to Tyr or Thr residues of their respective substrates (1–3). In the case of VopS and IbpA, several Rho family GTPases (Rac1, RhoA, and Cdc42) are known substrates and AMPylation disrupts the binding of the GTPase to its downstream effectors, for example, PAK1 (2–6). Considering the conservation of AMPylation domains in both prokaryotic and eukaryotic organisms, we expect that AMPylation plays an important role in a wide range of cellular processes (2, 4, 5, 7–9). Nevertheless, our understanding of this post-translational modification (PTM) is still limited to only a handful of known eukaryotic AMPylation substrates, exclusively belonging to the Rho and Rab GTPase families(10–14). Determining the repertoire of substrates modified by AMPylators will help illuminate both the functional consequences of AMPylation and the mechanistic strategies of pathogens that employ them (6).Significant effort has been devoted to identifying AMPylation substrates. Li et al. systematically investigated the fragmentation patterns of chemically synthesized peptides with Thr, Ser, and Tyr AMPylation using matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). They detected AMPylation sites with high confidence and selectively scanned AMPylated peptides in protein mixtures (10). Hao et al. produced a polyclonal antibody that specifically recognized proteins with AMPylation at threonine residues (11). Grammel et al. synthesized an ATP analog, N⁶pATP (N⁶-propargyl adenosine-5′-triphophate), which allows the labeling of AMPylated proteins with azide-functionalized fluorescein or a cleavable biotin enrichment tag (ortho-hydroxy-azidoethoxy-azobiotin) based on copper-catalyzed azide-alkyne cycloaddition (CuAAC)¹. The identification of new substrates for VopS in HeLa cell lysates was explored by a combination of AMP-specific pull-down and LC-MS (12). Using the same approach, Lewallen et al. tried to identify the substrates of VopS in MCF7 cell extracts by employing a commercial N⁶-(6-amino)hexyl-ATP-5-carboxyl-fluorescein (F1-ATP) and anti-fluorescein antibody(13). With these efforts combined, four potential new VopS substrates have been identified (SCCA2, NAGK, NME1, and PFKP), though not yet confirmed. These approaches might miss substrates because of temporal and spatial expression or low abundance in cell lysate, poor recognition by the capture molecules or loss during pull-down procedures (12, 14).Protein microarrays offer a promising approach to identify candidate substrates because they display thousands of unique proteins in a high-throughput and reproducible format (15–17). However, producing arrays with consistent levels of well-folded proteins is challenging because of limitations of protein production, purification, and storage, particularly for mammalian proteins (18).To circumvent these limitations, cell-free protein arrays, which do not require protein purification, have been developed over the past decade (19–22). These methods provide rapid and economical approaches of fabricating protein arrays in terms of cost, shelf life, and storage (23, 24). In cell-free protein arrays, a nucleotide template is printed on the slide and used to produce proteins in vitro with cell-free expression systems from several organisms such as E. coli, wheat germ, and rabbit reticulocyte lysate, etc. (24, 25). These proteins can be engineered to contain fusion tags that enable their capture to the array surface with an appropriate agent. Of these cell-free protein array methods, the Nucleic Acid Programmable Protein Array (NAPPA) is the most advanced, having achieved both high-density and high content containing ∼2300–8000 proteins per slide (20, 26, 27). In NAPPA, a plasmid-based cDNA configured to include an epitope tag is printed on a microscope slide along with the corresponding tag-specific binding reagent, such as an anti-tag antibody, and stored. At the time of experimentation, the cDNA is transcribed/translated into recombinant protein and captured/displayed in situ by the binding reagent. Using a rabbit reticulocyte lysate-based cell-free expression system, NAPPA has been applied toward the identification of novel protein-protein interactions and disease-related antibody biomarkers (20, 26, 28, 29). However, cell-free protein arrays have yet to be employed in the study of PTMs.In this work, we established a novel, nonradioactive unbiased AMPylation screening platform by developing a novel click chemistry-based detection assay for use on high-density cell-free protein microarrays displaying human proteins. Labeling AMP-modified substrates covalently with a fluorophore coupled with the use of human ribosomal machinery and chaperones to produce proteins achieved much higher sensitivity and signal to noise (S/N) ratio compared with previous studies. We screened 10,000 human proteins with two bacterial pathogen AMPylators, VopS and IbpAFic2, identifying more than twenty new substrates each. Two novel Rho GTPases (Rac2 and Rac3) were validated in vivo as substrates of the virulence factor VopS in HEK293T cells during V. para infection. Using mass spectrometry, we verified that a non-GTPase protein, ARHGDIB/LyGDI, was AMPylated by VopS on its threonine 51, which is located in a highly regulated part of this protein. This modification inhibited phosphorylation of LyGDI by Src kinase in vitro. Finally, the identification of these new targets allowed us to build the first bacteria-host interaction AMPylation network and may reveal signaling interactions that could potentially be important for bacterial pathogenesis in the future functional studies.     

Identification de C-glucosides flavoniques dans le genre Gentiana (section coelanthe)

Isoorientin, isovitexin, isoorientin-4′-O-glucoside and isovitexin-4′-O-glucoside have been identified in the leaves and roots of Gentiana punctata L., and in the leaves of G. purpurea L., G. pannonica Scop., G. villarsii Ronn., and G. burseri Lapeyr. Comparison with other gentians is discussed.