Ring-Opening Polymerization of ε-Caprolactone by Using Aluminum Complexes Bearing Aryl Thioether Phenolates: Labile Thioether Chelation.

In this study, aluminum complexes bearing ferrocene-based and arylthiomethylphenolate ligands were synthesized, and their catalytic activity for ε-caprolactone (CL) polymerization was investigated. The catalytic activity of the reduced form of Al complexes was higher than that of the oxidized form. The CL polymerization rate of the reduced form fcO2AlMe (75 min, conversion = 100%) was higher than that of the oxidized form fcoxO2AlMe (4320 min, conversion = 45%), and the CL polymerization rate of fc(OAlMe2)2 (40 min, conversion = 100%) was higher than that of fcox(OAlMe2)2 (60 min, conversion = 97%). Electron deficiency substituents on phenolate decreased the catalytic activity of Al complexes bearing arylthiomethylphenolate ligands. Density functional theory calculations revealed that thioether coordination stabilized the transition state (TS1) and that the oxidized form fcox(OAlMe2)2 exhibited weaker thioether coordination and higher activation energy in TS1 compared with those of the reduced form fcO2AlMe. In addition, our study determined that the thioether group is a suitable chelating group for Al catalysts in CL polymerization due to its labile nature.

SC5005 dissipates the membrane potential to kill Staphylococcus aureus persisters without detectable resistance.

OBJECTIVES: In the past few decades, multiple-antibiotic-resistant Staphylococcus aureus has emerged and quickly spread in hospitals and communities worldwide. Additionally, the formation of antibiotic-tolerant persisters and biofilms further reduces treatment efficacy. Previously, we identified a sorafenib derivative, SC5005, with bactericidal activity against MRSA in vitro and in vivo. Here, we sought to elucidate the resistance status, mode of action and anti-persister activity of this compound. METHODS: The propensity of S. aureus to develop SC5005 resistance was evaluated by assessment of spontaneous resistance and by multi-passage selection. The mode of action of SC5005 was investigated using macromolecular synthesis, LIVE/DEAD and ATPlite assays and DiOC2(3) staining. The effect of SC5005 on the mammalian cytoplasmic membrane was measured using haemolytic and lactate dehydrogenase (LDH) assays and flow cytometry. RESULTS: SC5005 depolarized and permeabilized the bacterial cytoplasmic membrane, leading to reduced ATP production. Because of this mode of action, no resistance of S. aureus to SC5005 was observed after constant exposure to sub-lethal concentrations for 200 passages. The membrane-perturbing activity of SC5005 was specific to bacteria, as no significant haemolysis or release of LDH from human HT-29 cells was detected. Additionally, compared with other bactericidal antibiotics, SC5005 exhibited superior activity in eradicating both planktonic and biofilm-embedded S. aureus persisters. CONCLUSIONS: Because of its low propensity for resistance development and potent persister-eradicating activity, SC5005 is a promising lead compound for developing new therapies for biofilm-related infections caused by S. aureus.

Siglecs at the Host-Pathogen Interface.

Siglecs are sialic acid (Sia) recognizing immunoglobulin-like receptors expressed on the surface of all the major leukocyte lineages in mammals. Siglecs recognize ubiquitous Sia epitopes on various glycoconjugates in the cell glycocalyx and transduce signals to regulate immunological and inflammatory activities of these cells. The subset known as CD33-related Siglecs is principally inhibitory receptors that suppress leukocyte activation, and recent research has shown that a number of bacterial pathogens use Sia mimicry to engage these Siglecs as an immune evasion strategy. Conversely, Siglec-1 is a macrophage phagocytic receptor that engages GBS and other sialylated bacteria to promote effective phagocytosis and antigen presentation for the adaptive immune response, whereas certain viruses and parasites use Siglec-1 to gain entry to immune cells as a proximal step in the infectious process. Siglecs are positioned in crosstalk with other host innate immune sensing pathways to modulate the immune response to infection in complex ways. This chapter summarizes the current understanding of Siglecs at the host-pathogen interface, a field of study expanding in breadth and medical importance, and which provides potential targets for immune-based anti-infective strategies.

Group B Streptococcus engages an inhibitory Siglec through sialic acid mimicry to blunt innate immune and inflammatory responses in vivo.

Group B Streptococcus (GBS) is a common agent of bacterial sepsis and meningitis in newborns. The GBS surface capsule contains sialic acids (Sia) that engage Sia-binding immunoglobulin-like lectins (Siglecs) on leukocytes. Here we use mice lacking Siglec-E, an inhibitory Siglec of myelomonocytic cells, to study the significance of GBS Siglec engagement during in vivo infection. We found GBS bound to Siglec-E in a Sia-specific fashion to blunt NF-κB and MAPK activation. As a consequence, Siglec-E-deficient macrophages had enhanced pro-inflammatory cytokine secretion, phagocytosis and bactericidal activity against the pathogen. Following pulmonary or low-dose intravenous GBS challenge, Siglec-E KO mice produced more pro-inflammatory cytokines and exhibited reduced GBS invasion of the central nervous system. In contrast, upon high dose lethal challenges, cytokine storm in Siglec-E KO mice was associated with accelerated mortality. We conclude that GBS Sia mimicry influences host innate immune and inflammatory responses in vivo through engagement of an inhibitory Siglec, with the ultimate outcome of the host response varying depending upon the site, stage and magnitude of infection.

Heparan Sulfate Modulates Neutrophil and Endothelial Function in Antibacterial Innate Immunity.

Recently, we showed that endothelial heparan sulfate facilitates entry of a bacterial pathogen into the central nervous system. Here, we show that normal bactericidal activity of neutrophils is influenced by the sulfation pattern of heparan sulfate. Inactivation of heparan sulfate uronyl 2-O-sulfotransferase (Hs2st) in neutrophils substantially reduced their bactericidal activity, and Hs2st deficiency rendered mice more susceptible to systemic infection with the pathogenic bacterium group B Streptococcus. Specifically, altered sulfation of heparan sulfate in mutant neutrophils affected formation of neutrophil extracellular traps while not influencing phagocytosis, production of reactive oxygen species, or secretion of granular proteases. Heparan sulfate proteoglycan(s) is present in neutrophil extracellular traps, modulates histone affinity, and modulates their microbial activity. Hs2st-deficient brain endothelial cells show enhanced binding to group B Streptococcus and are more susceptible to apoptosis, likely contributing to the observed increase in dissemination of group B Streptococcus into the brain of Hs2st-deficient mice following intravenous challenge. Taken together, our data provide strong evidence that heparan sulfate from both neutrophils and the endothelium plays important roles in modulating innate immunity.

Rapid evolution of binding specificities and expression patterns of inhibitory CD33-related Siglecs in primates.

Siglecs are sialic acid-binding Ig-like lectins that recognize sialoglycans via amino-terminal V-set domains. CD33-related Siglecs (CD33rSiglecs) on innate immune cells recognize endogenous sialoglycans as "self-associated molecular patterns" (SAMPs), dampening immune responses via cytosolic immunoreceptor tyrosine-based inhibition motifs that recruit tyrosine phosphatases. However, sialic acid-expressing pathogens subvert this mechanism through molecular mimicry. Meanwhile, endogenous host SAMPs must continually evolve to evade other pathogens that exploit sialic acids as invasion targets. We hypothesized that these opposing selection forces have accelerated CD33rSiglec evolution. We address this by comparative analysis of major CD33rSiglec (Siglec-3, Siglec-5, and Siglec-9) orthologs in humans, chimpanzees, and baboons. Recombinant soluble molecules displaying ligand-binding domains show marked quantitative and qualitative interspecies differences in interactions with strains of the sialylated pathogen, group B Streptococcus, and with sialoglycans presented as gangliosides or in the form of sialoglycan microarrays, including variations such as N-glycolyl and O-acetyl groups. Primate Siglecs also show quantitative and qualitative intra- and interspecies variations in expression patterns on leukocytes, both in circulation and in tissues. Taken together our data explain why the CD33rSiglec-encoding gene cluster is undergoing rapid evolution via multiple mechanisms, driven by the need to maintain self-recognition by innate immune cells, while escaping 2 distinct mechanisms of pathogen subversion.

The interplay between Siglecs and sialylated pathogens.

Siglecs are mammalian sialic acid (Sia) recognizing immunoglobulin-like receptors expressed across the major leukocyte lineages, and function to recognize ubiquitous Sia epitopes on cell surface glycoconjugates and regulate immunological and inflammatory activities of these cells. A large subset referred to as CD33-related Siglecs are inhibitory receptors that limit leukocyte activation, and recent research has shown that the pathogen group B Streptococcus (GBS) binds to these Siglecs in Sia- and protein-dependent fashion to downregulate leukocyte bactericidal capacity. Conversely, sialoadhesin is a macrophage phagocytic receptor that engages GBS and other sialylated pathogens to promote effective phagocytosis and antigen presentation for the adaptive immune response. A variety of other important Siglec interactions with bacterial, viral and protozoan pathogens are beginning to be recognized. Siglec genes and binding specificities are rapidly evolving among primates, with key extant polymorphisms in human populations that may influence susceptibility to infection-associated disorders including chronic obstructive pulmonary disease and premature birth. This review summarizes current understanding of interactions between pathogens and Siglecs, a field of investigation that is likely to continue expanding in scope and medical importance.

Decoy receptor 3 suppresses TLR2-mediated B cell activation by targeting NF-κB.

Decoy receptor 3 (DcR3) is a soluble protein in the TNFR superfamily. Its known ligands include Fas ligand, homologous to lymphotoxin, showing inducible expression, and competing with HSV glycoprotein D for herpes virus entry mediator, a receptor expressed by T lymphocytes, TNF-like molecule 1A, and heparan sulfate proteoglycans. DcR3 has been reported to modulate the functions of T cells, dendritic cells, and macrophages; however, its role in regulating B cell activation is largely unknown. In this study, we found that the DcR3.Fc fusion protein bound to human and mouse B cells and suppressed the activation of B cells. DcR3.Fc attenuated Staphylococcus aureus, IgM-, Pam(3)CSK(4)-, and LPS-mediated B cell proliferation but did not affect cytokine-induced B cell growth. In the presence of these mitogens, DcR3.Fc did not induce B cell apoptosis, suggesting that DcR3 may inhibit the signal(s) important for B cell activation. Because the combination of Fas.Fc, LT-ßR.Fc (homologous to lymphotoxin, showing inducible expression, and competing with HSV glycoprotein D for herpes virus entry mediator, a receptor expressed by T lymphocytes receptor), and DR3.Fc (TNF-like molecule 1A receptor) did not suppress B cell proliferation and because the biological effect of DcR3.Fc on B cells was not blocked by heparin, we hypothesize that a novel ligand(s) of DcR3 mediates its inhibitory activity on B cells. Moreover, we found that TLR2-stimulated NF-κB p65 activation and NF-κB-driven luciferase activity were attenuated by DcR3.Fc. The TLR2-induced cytokine production by B cells was consistently reduced by DcR3. These results imply that DcR3 may regulate B cell activation by suppressing the activation of NF-κB.

Loss of Siglec-14 reduces the risk of chronic obstructive pulmonary disease exacerbation.

Chronic obstructive pulmonary disease (COPD) is a leading cause of mortality worldwide. COPD exacerbation, or episodic worsening of symptoms, often results in hospitalization and increased mortality rates. Airway infections by new bacterial strains, such as nontypeable Haemophilus influenzae (NTHi), are a major cause of COPD exacerbation. NTHi express lipooligosaccharides that contain sialic acids, and may interact with Siglec-14, a sialic acid recognition protein on myeloid cells that serves as an activating signal transduction receptor. A null allele polymorphism in SIGLEC14 may attenuate the inflammatory responses to NTHi by eliminating Siglec-14 expression. We asked if the loss of Siglec-14 attenuates the inflammatory response by myeloid cells against NTHi, and if the SIGLEC14-null polymorphism has any effect on COPD exacerbation. We found that NTHi interacts with Siglec-14 to enhance proinflammatory cytokine production in a tissue culture model. Inhibitors of the Syk tyrosine kinase suppress this response. Loss of Siglec-14, due to SIGLEC14-null allele homozygosity, is associated with a reduced risk of COPD exacerbation in a Japanese patient population. Taken together, Siglec-14 and its downstream signaling pathway facilitate the "infection-inflammation-exacerbation" axis of COPD disease progression, and may represent promising targets for therapeutic intervention.

Conserved molecular chaperone PrsA stimulates protective immunity against group A Streptococcus.

Group A Streptococcus (GAS) is a significant human pathogen that poses a global health concern. However, the development of a GAS vaccine has been challenging due to the multitude of diverse M-types and the risk of triggering cross-reactive immune responses. Our previous research has identified a critical role of PrsA1 and PrsA2, surface post-translational molecular chaperone proteins, in maintaining GAS proteome homeostasis and virulence traits. In this study, we aimed to further explore the potential of PrsA1 and PrsA2 as vaccine candidates for preventing GAS infection. We found that PrsA1 and PrsA2 are highly conserved among GAS isolates, demonstrating minimal amino acid variation. Antibodies specifically targeting PrsA1/A2 showed no cross-reactivity with human heart proteins and effectively enhanced neutrophil opsonophagocytic killing of various GAS serotypes. Additionally, passive transfer of PrsA1/A2-specific antibodies conferred protective immunity in infected mice. Compared to alum, immunization with CFA-adjuvanted PrsA1/A2 induced higher levels of Th1-associated IgG isotypes and complement activation and provided approximately 70% protection against invasive GAS challenge. These findings highlight the potential of PrsA1 and PrsA2 as universal vaccine candidates for the development of an effective GAS vaccine.

Glycosaminoglycan binding facilitates entry of a bacterial pathogen into central nervous systems.

Certain microbes invade brain microvascular endothelial cells (BMECs) to breach the blood-brain barrier (BBB) and establish central nervous system (CNS) infection. Here we use the leading meningitis pathogen group B Streptococcus (GBS) together with insect and mammalian infection models to probe a potential role of glycosaminoglycan (GAG) interactions in the pathogenesis of CNS entry. Site-directed mutagenesis of a GAG-binding domain of the surface GBS alpha C protein impeded GBS penetration of the Drosophila BBB in vivo and diminished GBS adherence to and invasion of human BMECs in vitro. Conversely, genetic impairment of GAG expression in flies or mice reduced GBS dissemination into the brain. These complementary approaches identify a role for bacterial-GAG interactions in the pathogenesis of CNS infection. Our results also highlight how the simpler yet genetically conserved Drosophila GAG pathways can provide a model organism to screen candidate molecules that can interrupt pathogen-GAG interactions for future therapeutic applications.

The Src-ZNRF1 axis controls TLR3 trafficking and interferon responses to limit lung barrier damage.

Type I interferons are important antiviral cytokines, but prolonged interferon production is detrimental to the host. The TLR3-driven immune response is crucial for mammalian antiviral immunity, and its intracellular localization determines induction of type I interferons; however, the mechanism terminating TLR3 signaling remains obscure. Here, we show that the E3 ubiquitin ligase ZNRF1 controls TLR3 sorting into multivesicular bodies/lysosomes to terminate signaling and type I interferon production. Mechanistically, c-Src kinase activated by TLR3 engagement phosphorylates ZNRF1 at tyrosine 103, which mediates K63-linked ubiquitination of TLR3 at lysine 813 and promotes TLR3 lysosomal trafficking and degradation. ZNRF1-deficient mice and cells are resistant to infection by encephalomyocarditis virus and SARS-CoV-2 because of enhanced type I interferon production. However, Znrf1-/- mice have exacerbated lung barrier damage triggered by antiviral immunity, leading to enhanced susceptibility to respiratory bacterial superinfections. Our study highlights the c-Src-ZNRF1 axis as a negative feedback mechanism controlling TLR3 trafficking and the termination of TLR3 signaling.

Persistent Krüppel-like factor 4 expression predicts progression and poor prognosis of head and neck squamous cell carcinoma.

Head and neck squamous cell carcinoma (HNSCC) is one prevalent human cancer worldwide. No molecular markers are presently used for predicting prognosis in HNSCC. Krüppel-like factor 4 (KLF4) is a transcription factor with diverse physiological functions, and possesses opposing roles in different human cancers. The expression and roles of KLF4 in HNSCC remain to be elucidated. In this study, immunohistochemical (IHC) analysis of KLF4 in 62 HNSCC was firstly performed. IHC results demonstrated that 42 (67.7%) had decreased KLF4 expression compared with surrounding normal epithelium, while persistent KLF4 expression was demonstrated in 20 (32.3%). The IHC results were further verified by Western blot and real-time PCR analyses to confirm the robustness of staining and interpretation. Interestingly, persistent KLF4 expression independently correlated with a worse disease-specific survival (P = 0.005), especially in patients with advanced disease. In consistent with clinical observation, all five HNSCC cell lines tested revealed a low level of baseline KLF4 expression. Moreover, enforced KLF4 expression in cell line SAS significantly increased in vitro migration/invasion abilities, multi-drug resistance, and in vivo tumorigenicity. These results clearly illustrate that persistent KLF4 expression predicts poor prognosis and confers aggressiveness in HNSCC. Our data therefore provides valuable information that HNSCC with persistent KLF4 expression might require intensified combination treatment in future practice.

Molecular mimicry of host sialylated glycans allows a bacterial pathogen to engage neutrophil Siglec-9 and dampen the innate immune response.

Human neutrophil Siglec-9 is a lectin that recognizes sialic acids (Sias) via an amino-terminal V-set Ig domain and possesses tyrosine-based inhibitory motifs in its cytoplasmic tail. We hypothesized that Siglec-9 recognizes host Sias as "self," including in cis interactions with Sias on the neutrophil's own surface, thereby dampening unwanted neutrophil reactivity. Here we show that neutrophils presented with immobilized multimerized Siaalpha2-3Galbeta1-4GlcNAc units engage them in trans via Siglec-9. The sialylated capsular polysaccharide of group B Streptococcus (GBS) also presents terminal Siaalpha2-3Galbeta1-4GlcNAc units, and similarly engages neutrophil Siglec-9, dampening neutrophil responses in a Sia- and Siglec-9-dependent manner. Reduction in the neutrophil oxidative burst, diminished formation of neutrophil extracellular DNA traps, and increased bacterial survival are also facilitated by GBS sialylated capsular polysaccharide interactions with Siglec-9. Thus, GBS can impair neutrophil defense functions by coopting a host inhibitory receptor via sialoglycan molecular mimicry, a novel mechanism of bacterial immune evasion.

Novel Virulence Role of Pneumococcal NanA in Host Inflammation and Cell Death Through the Activation of Inflammasome and the Caspase Pathway.

Streptococcus pneumoniae is one of most deadly Gram-positive bacterium that causes significant mortality and morbidity worldwide. Intense inflammation and cytotoxicity is a hallmark of invasive pneumococcal disease. Pneumococcal NanA has been shown to exaggerate the production of inflammatory cytokines via unmasking of inhibitory Siglec-5 from its sialyl cis-ligands. To further investigate the mechanistic role of NanA and Siglec-5 in pneumococccal diseases, we systemically analyzed genes and signaling pathways differentially regulated in macrophages infected with wild type and NanA-deficient pneumococcus. We found that NanA-mediated desialylation impairs the Siglec-5-TLR-2 interaction and reduces the recruitment of phosphatase SHP-1 to Siglec-5. This dysregulated crosstalk between TLR-2 and inhibitory Siglec-5 exaggerated multiple inflammatory and death signaling pathways and consequently caused excessive inflammation and cytotoxicity in the infected macrophage. Collectively, our results reveal a novel virulence role of NanA in pneumococcal pathogenesis and suggest that targeting NanA activity may ameliorate the pneumococcus-mediated inflammation and cytotoxicity in severe invasive pneumococcal diseases.

Therapeutic Development Based on the Immunopathogenic Mechanisms of Psoriasis.

Psoriasis, a complex inflammatory autoimmune skin disorder that affects 2-3% of the global population, is thought to be genetically predetermined and induced by environmental and immunological factors. In the past decades, basic and clinical studies have significantly expanded knowledge on the molecular, cellular, and immunological mechanisms underlying the pathogenesis of psoriasis. Based on these pathogenic mechanisms, the current disease model emphasizes the role of aberrant Th1 and Th17 responses. Th1 and Th17 immune responses are regulated by a complex network of different cytokines, including TNF-α, IL-17, and IL-23; signal transduction pathways downstream to the cytokine receptors; and various activated transcription factors, including NF-κB, interferon regulatory factors (IRFs), and signal transducer and activator of transcriptions (STATs). The biologics developed to specifically target the cytokines have achieved a better efficacy and safety for the systemic management of psoriasis compared with traditional treatments. Nevertheless, the current therapeutics can only alleviate the symptoms; there is still no cure for psoriasis. Therefore, the development of more effective, safe, and affordable therapeutics for psoriasis is important. In this review, we discussed the current trend of therapeutic development for psoriasis based on the recent discoveries in the immune modulation of the inflammatory response in psoriasis.

Unique virulence role of post-translocational chaperone PrsA in shaping Streptococcus pyogenes secretome.

Streptococcus pyogenes (group A Streptococcus, GAS) is a strict human pathogen causing a broad spectrum of diseases and a variety of autoimmune sequelae. The pathogenesis of GAS infection mostly relies on the production of an extensive network of cell wall-associated and secreted virulence proteins, such as adhesins, toxins, and exoenzymes. PrsA, the only extracellular parvulin-type peptidyl-prolyl isomerase expressed ubiquitously in Gram-positive bacteria, has been suggested to assist the folding and maturation of newly exported proteins to acquire their native conformation and activity. Two PrsA proteins, PrsA1 and PrsA2, have been identified in GAS, but the respective contribution of each PrsA in GAS pathogenesis remains largely unknown. By combining comparative proteomic and phenotypic analysis approaches, we demonstrate that both PrsA isoforms are required to maintain GAS proteome homeostasis and virulence-associated traits in a unique and overlapping manner. The inactivation of both PrsA in GAS caused remarkable impairment in biofilm formation, host adherence, infection-induced cytotoxicity, and in vivo virulence in a murine soft tissue infection model. The concordance of proteomic and phenotypic data clearly features the essential role of PrsA in GAS full virulence.

Epigenetic control of MHC class II expression in tumor-associated macrophages by decoy receptor 3.

Decoy receptor 3 (DcR3) is a member of the TNF receptor superfamily and is up-regulated in tumors originating from a diversity of lineages. DcR3 is capable of promoting angiogenesis, inducing dendritic cell apoptosis, and modulating macrophage differentiation. Since tumor-associated macrophages (TAMs) are the major infiltrating leukocytes in most malignant tumors, we used microarray technology to investigate whether DcR3 contributes to the development of TAMs. Among the DcR3-modulated genes expressed by TAMs, those that encode proteins involved in MHC class II (MHC-II)-dependent antigen presentation were down-regulated substantially, together with the master regulator of MHC-II expression (the class II transactivator, CIITA). The ERK- and JNK-induced deacetylation of histones associated with the CIITA promoters was responsible for DcR3-mediated down-regulation of MHC-II expression. Furthermore, the expression level of DcR3 in cancer cells correlated inversely with HLA-DR levels on TAMs and with the overall survival time of pancreatic cancer patients. The role of DcR3 in the development of TAMs was further confirmed using transgenic mice overexpressing DcR3. This elucidates the molecular mechanism of impaired MHC-II-mediated antigen presentation by TAMs, and raises the possibility that subversion of TAM-induced immunosuppression via inhibition of DcR3 expression might represent a target for the design of new therapeutics.

T4 Pili Promote Colonization and Immune Evasion Phenotypes of Nonencapsulated M4 Streptococcus pyogenes.

Streptococcus pyogenes (group A Streptococcus [GAS]) is an important human pathogen causing a broad spectrum of diseases and associated with significant global morbidity and mortality. Almost all GAS isolates express a surface hyaluronic acid capsule, a virulence determinant that facilitates host colonization and impedes phagocyte killing. However, recent epidemiologic surveillance has reported a sustained increase in both mucosal and invasive infections caused by nonencapsulated GAS, which questions the indispensable role of hyaluronic acid capsule in GAS pathogenesis. In this study, we found that pilus of M4 GAS not only significantly promotes biofilm formation, adherence, and cytotoxicity to human upper respiratory tract epithelial cells and keratinocytes, but also promotes survival in human whole blood and increased virulence in murine models of invasive infection. T4 antigen, the pilus backbone protein of M4 GAS, binds haptoglobin, an abundant human acute-phase protein upregulated upon infection and inflammation, on the bacterial surface. Haptoglobin sequestration reduces the susceptibility of nonencapsulated M4 GAS to antimicrobial peptides released from activated neutrophils and platelets. Our results reveal a previously unappreciated virulence-promoting role of M4 GAS pili, in part mediated by co-opting the biology of haptoglobin to mitigate host antimicrobial defenses.IMPORTANCE Group A Streptococcus (GAS) is a strict human pathogen causing more than 700 million infections globally each year. The majority of the disease-causing GAS are encapsulated, which greatly guarantees survival and dissemination in the host. Emergence of the capsule-negative GAS, such as M4 GAS, in recent epidemiologic surveillance alarms the necessity to elucidate the virulence determinants of these pathogens. Here, we found that M4 pili play an important role in promoting M4 GAS adherence and cytotoxicity to human pharyngeal epithelial cells and keratinocytes. The same molecule also significantly enhanced M4 GAS survival and replication in human whole blood and experimental murine infection. T4 antigen, which composes the backbone of M4 pili, was able to sequester the very abundant serum protein haptoglobin to further confer M4 GAS resistance to antibacterial substances released by neutrophils and platelets.

Use of pyrazoles as ligands greatly enhances the catalytic activity of titanium iso-propoxide for the ring-opening polymerization of l-lactide: a cooperation effect.

Using TiOiPr4 with a pyrazole ligand for one-pot LA polymerization improved catalytic activity compared with using TiOiPr4 only. At 60 °C, TiOiPr4 with furPz exhibited a higher catalytic activity (approximately 3-fold) than TiOiPr4. At room temperature, TiOiPr4 with BuPz exhibited a higher catalytic activity (approximately 17-fold) than TiOiPr4. High molecular mass PLA (M nGPC = 51 100, and D = 1.10) could be produced by using TiOiPr4 with furPz in melt polymerization ([TiOiPr4] : [furPz] = 1000 : 1 : 1 at 100 °C, 240 min). The crystal structure of MePz2Ti2OiPr7 revealed the cooperative activation between two Ti atoms during LA polymerization.