The crystal structure of lipopolysaccharide binding protein reveals the location of a frequent mutation that impairs innate immunity.

Lipopolysaccharide (LPS) binding protein (LBP) is an acute-phase protein that initiates an immune response after recognition of bacterial LPS. Here, we report the crystal structure of murine LBP at 2.9 Å resolution. Several structural differences were observed between LBP and the related bactericidal/permeability-increasing protein (BPI), and the LBP C-terminal domain contained a negatively charged groove and a hydrophobic "phenylalanine core." A frequent human LBP SNP (allelic frequency 0.08) affected this region, potentially generating a proteinase cleavage site. The mutant protein had a reduced binding capacity for LPS and lipopeptides. SNP carriers displayed a reduced cytokine response after in vivo LPS exposure and lower cytokine concentrations in pneumonia. In a retrospective trial, the LBP SNP was associated with increased mortality rates during sepsis and pneumonia. Thus, the structural integrity of LBP may be crucial for fighting infections efficiently, and future patient stratification might help to develop better therapeutic strategies.

STING SNP R293Q Is Associated with a Decreased Risk of Aging-Related Diseases.

BACKGROUND: Aging is a multifactorial process driven by several conditions. Among them, inflamm-aging is characterized by chronic low-grade inflammation driving aging-related diseases. The aged immune system is characterized by the senescence-associated secretory phenotype, resulting in the release of proinflammatory cytokines contributing to inflamm-aging. Another possible mechanism resulting in inflamm-aging could be the increased release of danger- associated molecular patterns (DAMPs) by increased cell death in the elderly, leading to a chronic low-grade inflammatory response. Several pattern recognition receptors of the innate immune system are involved in recognition of DAMPs. The DNA-sensing cGAS-STING pathway plays a pivotal role in combating viral and bacterial infections and recognizes DNA released by cell death during the process of aging, which in turn may result in increased inflamm-aging. OBJECTIVE: The aim of this study was to investigate whether a variation within the STING gene with known impaired function may be associated with protection from aging-related diseases by decreasing the process of inflamm-aging. METHODS: STING (Tmem173) R293Q was genotyped in a cohort of 3,397 aged subjects (65-103 years). The distribution of the variant allele in healthy subjects and subjects suffering from aging-associated diseases was compared by logistic regression analysis. RESULTS: We show here that STING 293Q allele carriers were protected from aging-associated diseases (OR = 0.823, p = 0.038). This effect was much stronger in the subgroup of subjects suffering from chronic lung diseases (OR = 0.730, p = 0.009). CONCLUSION: Our results indicate that decreased sensitivity of the innate immune receptors is associated with healthy aging, most likely due to a decreased process of inflamm-aging.

A Genetic Variation of Lipopolysaccharide Binding Protein Affects the Inflammatory Response and Is Associated with Improved Outcome during Sepsis.

LPS binding protein (LBP) is an important innate sensor of microbial cell wall structures. Frequent functionally relevant mutations exist and have been linked to influence susceptibility to and course of bacterial infections. We examined functional properties of a single nucleotide polymorphism resulting in an exchange of phenylalanine to leucine at position 436 of LBP (rs2232618) and compared the frequent variant of the molecule with the rare one in ligand binding experiments. We then stimulated RAW cells with bacterial ligands in the presence of serum obtained from individuals with different LBP genotypes. We, furthermore, determined the potential effects of structural changes in the molecule by in silico modeling. Finally, we analyzed 363 surgical patients for this genetic variant and examined incidence and course of sepsis following surgery. We found that binding of LBP to bacterial ligands was reduced, and stimulation of RAW cells resulted in an increased release of TNF when adding serum from individuals carrying the F436L variant as compared with normal LBP. In silico analysis revealed structural changes of LBP, potentially explaining some of the effects observed for the LBP variant. Finally, patients carrying the F436L variant were found to be similarly susceptible for sepsis. However, we observed a more favorable course of severe infections in this cohort. Our findings reveal new insights into LPS recognition and the subsequent activation of the innate immune system brought about by LBP. The identification of a genetic variant of LBP influencing the course of sepsis may help to stratify individuals at risk and thus reduce clinical complications of patients.

Effects of cyanobacterial toxins and cyanobacterial cell-free crude extract on germination of alfalfa (Medicago sativa) and induction of oxidative stress.

Cyanobacterial toxins have adverse effects on both terrestrial and aquatic plants. Microcystins are cyclic heptapeptides and an important group of cyanotoxins. When lake water contaminated with cyanobacterial blooms is used for spray irrigation, these toxins can come in contact with agricultural plants. During the exposure to these toxins, reactive oxygen species can form. These reactive oxygen species have a strong reactivity and are able to interact with other cellular compounds (lipids, protein, and DNA). Plants have antioxidative systems that will limit the negative effects caused by reactive oxygen species. These systems consist of enzymes, such as superoxide dismutase, catalase, and ascorbate peroxidase, and nonenzymatic substances, such as reduced glutathione or vitamins. The aim of the present study was to investigate the effects of cyanobacterial toxins (microcystins and anatoxin-a) and cyanobacterial cell-free crude extract on alfalfa (Medicago sativa) seedlings. Inhibition of germination and root growth was observed with toxin concentrations of 5.0 microg/L. Also, oxidative damage, such as lipid peroxidation, was detected after the exposure of alfalfa seedlings to the toxin. Reactive oxygen detoxifying enzymes were elevated, showing a marked response in alfalfa to oxidative stress caused by the exposure to cyanobacterial metabolites that might influence the growth and development of these plants negatively.