The role of lipid II in membrane binding of and pore formation by nisin analyzed by two combined biosensor techniques

Nisin, a peptide antibiotic, efficiently kills bacteria through a unique mechanism which includes inhibition of cell wall biosynthesis and pore formation in cytoplasmic membranes. Both mechanisms are based on interaction with the cell wall precursor lipid II which is simultaneously used as target and pore constituent. We combined two biosensor techniques to investigate the nisin activity with respect to membrane binding and pore formation in real time. Quartz crystal microbalance (QCM) allows the detection of nisin binding kinetics. The presence of 0.1 mol% lipid II strongly increased nisin binding affinity to DOPC (k_D 2.68 × 10^− 7 M vs. 1.03 × 10^− 6 M) by a higher association rate. Differences were less pronounced while using negatively charged DOPG membranes. However, lipid II does not influence the absolute amount of bound nisin. Cyclic voltammetry (CV) data confirmed that in presence of 0.1 mol% lipid II, nanomolar nisin concentrations were sufficient to form pores, while micromolar concentrations were necessary in absence of lipid II. Both techniques suggested unspecific destruction of pure DOPG membranes by micromolar nisin concentrations which were prevented by lipid II. This model membrane stabilization by lipid II was confirmed by atomic force microscopy. Combined CV and QCM are valuable to interpret the role of lipid II in nisin activity.     

Genetic Variants in Genes of the Inflammatory Response in Association with Infective Endocarditis

Aims

Inflammation in infective endocarditis (IE) is a complex network including interactions of inflammatory cytokines and other components of host response. Certainly, any variation in this network could influence susceptibility or disease progression of IE. In this study, 14 single nucleotide variants (SNVs) in genes coding for interleukin-1β, interleukin-6, interleukin-10, toll–like receptor-4, tumor necrosis factor-α, selectin E and intercellular adhesion molecule-1 were analyzed for an association with susceptibility to IE and correlated with disease-related laboratory parameters. Furthermore, the occurrence of SNVs was examined to elucidate pathogen-dependent associations.

Methods and Results

The distribution of SNVs was determined in IE-patients and healthy blood donors by RFLP analysis. White blood cells (WBC) were counted using flow cytometry, concentration of C-reactive protein and procalcitonin was measured immunologically. Interleukin-6 c.471+870G>A genotypes differed significantly between IE patients and controls. The frequency of the heterozygote genotype GA was considerably higher in the patient group (68.9% vs. 43.8%, P_c<0.0003). Interleukin-6 c.-237 minor allele frequency was increased in patients, although not statistically significant. Additionally, we detected a potential relation between interleukin-1β c.315C>T and IE. Pathogen-dependent analysis showed no significantly associated subgroup in relation to IE susceptibility, but gave hints towards alterations regarding Enterococcus-caused IE cases. Patients with genotype selectin-E c.-19 GT tend to have higher preoperative WBC counts than patients with genotype GG. We further showed an association between two interleukin-1β SNVs and laboratory biomarkers.

Conclusion

This study shows genetic predispositions for the establishment of IE. Furthermore, correlation of SNVs with disease-related biomarkers suggests a role of genetic variants regarding the inflammatory response in IE.     

In-Depth Investigation of Archival and Prospectively Collected Samples Reveals No Evidence for XMRV Infection in Prostate Cancer

XMRV, or xenotropic murine leukemia virus (MLV)-related virus, is a novel gammaretrovirus originally identified in studies that analyzed tissue from prostate cancer patients in 2006 and blood from patients with chronic fatigue syndrome (CFS) in 2009. However, a large number of subsequent studies failed to confirm a link between XMRV infection and CFS or prostate cancer. On the contrary, recent evidence indicates that XMRV is a contaminant originating from the recombination of two mouse endogenous retroviruses during passaging of a prostate tumor xenograft (CWR22) in mice, generating laboratory-derived cell lines that are XMRV-infected. To confirm or refute an association between XMRV and prostate cancer, we analyzed prostate cancer tissues and plasma from a prospectively collected cohort of 39 patients as well as archival RNA and prostate tissue from the original 2006 study. Despite comprehensive microarray, PCR, FISH, and serological testing, XMRV was not detected in any of the newly collected samples or in archival tissue, although archival RNA remained XMRV-positive. Notably, archival VP62 prostate tissue, from which the prototype XMRV strain was derived, tested negative for XMRV on re-analysis. Analysis of viral genomic and human mitochondrial sequences revealed that all previously characterized XMRV strains are identical and that the archival RNA had been contaminated by an XMRV-infected laboratory cell line. These findings reveal no association between XMRV and prostate cancer, and underscore the conclusion that XMRV is not a naturally acquired human infection.     

Peroxisome Formation Requires the Endoplasmic Reticulum Channel Protein Sec61

In peroxisome formation, models of near‐autonomous peroxisome biogenesis with membrane protein integration directly from the cytosol into the peroxisomal membrane are in direct conflict with models whereby peroxisomes bud from the endoplasmic reticulum and receive their membrane proteins through a branch of the secretory pathway. We therefore reinvestigated the role of the Sec 61 complex, the protein‐conducting channel of the endoplasmic reticulum (ER) in peroxisome formation. We found that depletion or partial inactivation of Sec 61 in yeast disables peroxisome formation. The ER entry of the early peroxisomal membrane protein Pex 3 engineered with a glycosylation tag is reduced in sec61 mutant cells. Moreover, we were able to reconstitute Pex 3 import into ER membranes in vitro, and we identified a variant of a signal anchor sequence for ER translocation at the Pex 3 N‐terminus. Our findings are consistent with a Sec 61 requirement for peroxisome formation and a fundamental role of the ER in peroxisome biogenesis.     

A <Emphasis Type="Italic">de novo</Emphasis> germline mutation in <Emphasis Type="Italic">MYH7</Emphasis> causes a progressive dominant myopathy in pigs

Background

About 9% of the offspring of a clinically healthy Piétrain boar named ‘Campus’ showed a progressive postural tremor called Campus syndrome (CPS). Extensive backcross experiments suggested a dominant mode of inheritance, and the founder boar was believed to be a gonadal mosaic. A genome-scan mapped the disease-causing mutation to an 8 cM region of porcine chromosome 7 containing the MHY7 gene. Human distal myopathy type 1 (MPD1), a disease partially resembling CPS in pigs, has been associated with mutations in the MYH7 gene.

Results

The porcine MYH7 gene structure was predicted based on porcine reference genome sequence, porcine mRNA, and in comparison to the human ortholog. The gene structure was highly conserved with the exception of the first exon. Mutation analysis of a contiguous genomic interval of more than 22 kb spanning the complete MYH7 gene revealed an in-frame insertion within exon 30 of MYH7 (c.4320_4321insCCCGCC) which was perfectly associated with the disease phenotype and confirmed the dominant inheritance. The mutation is predicted to insert two amino acids (p.Ala1440_Ala1441insProAla) in a very highly conserved region of the myosin tail. The boar ‘Campus’ was shown to be a germline and somatic mosaic as assessed by the presence of the mutant allele in seven different organs.

Conclusion

This study illustrates the usefulness of recently established genomic resources in pigs. We have identified a spontaneous mutation in MYH7 as the causative mutation for CPS. This paper describes the first case of a disorder caused by a naturally occurring mutation in the MYH7 gene of a non-human mammalian species. Our study confirms the previous classification as a primary myopathy and provides a defined large animal model for human MPD1. We provide evidence that the CPS mutation occurred during the early development of the boar ‘Campus’. Therefore, this study provides an example of germline mosaicism with an asymptomatic founder.

     

Membrane Lipids Determine the Antibiotic Activity of the Lantibiotic Gallidermin

Lantibiotics, a group of lanthionine-containing peptides, display their antibiotic activity by combining different killing mechanisms within one molecule. The prototype lantibiotic nisin was shown to possess both inhibition of peptidoglycan synthesis and pore formation in bacterial membranes by interacting with lipid II. Gallidermin, which shares the lipid II binding motif with nisin but has a shorter molecular length, differed from nisin in pore formation in several strains of bacteria. To simulate the mode of action, we applied cyclic voltammetry and quartz crystal microbalance to correlate pore formation with lipid II binding kinetics of gallidermin in model membranes. The inability of gallidermin to form pores in DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) (C18/1) and DPoPC (1,2-dipalmitoleoyl-sn-glycero-3-phosphocholine) (C16/1) membranes was related to the membrane thickness. For a better simulation of bacterial membrane characteristics, two different phospholipids with branched fatty acids were incorporated into the DPoPC matrix. Phospholipids with methyl branches in the middle of the fatty acid chains favored a lipid II–independent DPoPC permeabilization by gallidermin, while long-branched phospholipids in which the branch is placed near the hydrophilic region induced an identical lipid II–dependent pore formation of gallidermin and nisin. Obviously, the branched lipids altered lipid packing and reduced the membrane thickness. Therefore, the duality of gallidermin activity (pore formation and inhibition of the cell wall synthesis) seems to be balanced by the bacterial membrane composition.