Latency of Infection in Unripe Avocados by Colletotrichum gloeosporioides is Not Due to Inadequate Enzyme Potential

Colletotrichum gloeosporioides produced exo-pectin lyase and protease in a) liquid cultures with incorporated washed cell wall material from unripe or ripe avocado and b) autoclaved immature fruit. The activity of exo-pectin lyase and protease produced in liquid cultures incorporating washed cell walls from immature fruits was almost the same as when washed cell walls from ripe fruits were incorporated. Ripe fruit tissue rotted by the fungus contained exo-pectin lyase, endo-polygalacturonase (endo-PG) and protease. The endo-PG was found to be endogenous to avocado fruit, and had a pH optimum of 5.5. The pH optima of exo-pectin lyase and protease were 8.5 and 7.5 respectively in all three enzyme preparations. All these enzyme preparations completely macerated avocado fruit tissue discs in vitro in less than 3 h of incubation but not potato tuber discs. Neither immature nor ripe fruit contained substances, proteinaceous or otherwise, which could inhibit the exo-pectin lyase or protease activity of these preparations. The results indicated that C. gloeosporioides possesses sufficient enzyme potential to invade cell walls of unripe fruit and that the fruit tissue does not have a mechanism to inactivate such enzymes.     

Selective removal of closely related clipped protein impurities using poly(ethylenimine)- grafted anion-exchange chromatography resin

Abstract

Proteolytic degradation is a serious problem that complicates downstream processing during production of recombinant therapeutic proteins. It can lead to decreased product yield, diminished biological activity, and suboptimal product quality. Proteolytic degradation or protein truncation is observed in various expression hosts and is mostly attributed to the activity of proteases released by host cells. Since these clipped proteins can impact pharmacokinetics and immunogenicity in addition to potency, they need to be appropriately controlled to ensure consistency of product quality and patient safety. A chromatography step for the selective removal of clipped proteins from an intact protein was developed in this study. Poly(ethylenimine)-grafted anion- exchange resins (PolyQUAT and PolyPEI) were evaluated and compared to traditional macroporous anion-exchange and tentacled anion-exchange resins. Isocratic retention experiments were conducted to determine the retention factors (k′) and charge factors (Z) were determined through the classical stoichiometric displacement model. High selectivity in separation of closely related clipped proteins was obtained with the PolyQUAT resin. A robust design space was established for the PolyQUAT chromatography through Design-Of-Experiments (DoE) based process optimization. Results showed a product recovery of up to 63% with purity levels >99.0%. Approximately, one-log clearance of host cell protein and two-logs clearance of host cell DNA were also obtained. The newly developed PolyQUAT process was compared with an existing process and shown to be superior with respect to the number of process steps, process time, process yield, and product quality.     

Pre-Dialysis Systolic Blood Pressure-Variability Is Independently Associated with All-Cause Mortality in Incident Haemodialysis Patients

Systolic blood pressure variability is an independent risk factor for mortality and cardiovascular events. Standard measures of blood pressure predict outcome poorly in haemodialysis patients. We investigated whether systolic blood pressure variability was associated with mortality in incident haemodialysis patients. We performed a longitudinal observational study of patients commencing haemodialysis between 2005 and 2011 in East Anglia, UK, excluding patients with cardiovascular events within 6 months of starting haemodialysis. The main exposure was variability independent of the mean (VIM) of systolic blood pressure from short-gap, pre-dialysis blood pressure readings between 3 and 6 months after commencing haemodialysis, and the outcome was all-cause mortality. Of 203 patients, 37 (18.2%) patients died during a mean follow-up of 2.0 (SD 1.3) years. The age and sex-adjusted hazard ratio (HR) for mortality was 1.09 (95% confidence interval (CI) 1.02–1.17) for a one-unit increase of VIM. This was not altered by adjustment for diabetes, prior cardiovascular disease and mean systolic blood pressure (HR 1.09, 95% CI 1.02–1.16). Patients with VIM of systolic blood pressure above the median were 2.4 (95% CI 1.17–4.74) times more likely to die during follow-up than those below the median. Results were similar for all measures of blood pressure variability and further adjustment for type of dialysis access, use of antihypertensives and absolute or variability of fluid intake did not alter these findings. Diastolic blood pressure variability showed no association with all cause mortality. Our study shows that variability of systolic blood pressure is a strong and independent predictor of all-cause mortality in incident haemodialysis patients. Further research is needed to understand the mechanism as this may form a therapeutic target or focus for management.     

KOPS-guided DNA translocation by FtsK safeguards Escherichia coli chromosome segregation

The septum-located DNA translocase, FtsK, acts to co-ordinate the late steps of Escherichia coli chromosome segregation with cell division. The FtsK γ regulatory subdomain interacts with 8 bp KOPS DNA sequences, which are oriented from the replication origin to the terminus region ( ter ) in each arm of the chromosome. This interaction directs FtsK translocation towards ter where the final chromosome unlinking by decatenation and chromosome dimer resolution occurs. Chromosome dimer resolution requires FtsK translocation along DNA and its interaction with the XerCD recombinase bound to the recombination site, dif , located within ter . The frequency of chromosome dimer formation is ∼15% per generation in wild-type cells. Here we characterize FtsK alleles that no longer recognize KOPS, yet are proficient for translocation and chromosome dimer resolution. Non-directed FtsK translocation leads to a small reduction in fitness in otherwise normal cell populations, as a consequence of ∼70% of chromosome dimers being resolved to monomers. More serious consequences arise when chromosome dimer formation is increased, or their resolution efficiency is impaired because of defects in chromosome organization and processing. For example, when Cre– loxP recombination replaces XerCD– dif recombination in dimer resolution, when functional MukBEF is absent, or when replication terminates away from ter .     

FtsK translocation on DNA stops at XerCD-dif

Escherichia coli FtsK is a powerful, fast, double-stranded DNA translocase, which can strip proteins from DNA. FtsK acts in the late stages of chromosome segregation by facilitating sister chromosome unlinking at the division septum. KOPS-guided DNA translocation directs FtsK towards dif, located within the replication terminus region, ter, where FtsK activates XerCD site-specific recombination. Here we show that FtsK translocation stops specifically at XerCD-dif, thereby preventing removal of XerCD from dif and allowing activation of chromosome unlinking by recombination. Stoppage of translocation at XerCD-dif is accompanied by a reduction in FtsK ATPase and is not associated with FtsK dissociation from DNA. Specific stoppage at recombinase-DNA complexes does not require the FtsKγ regulatory subdomain, which interacts with XerD, and is not dependent on either recombinase-mediated DNA cleavage activity, or the formation of synaptic complexes.     

Biological Activity of Four Antifungal Compounds in Immature Avocado

Anthracnose caused by Colletotrichum gloeosporioides in ripe avocados originates as latent infections in the immature fruits. Concentrated ether extract of the peel of apparently healthy, immature avocados when bioassayed on thin layer chromatographic plates with conidia of either Cladosporium cladosporioides or C. gloeosporioides produced four inhibition areas at Rf 0.30, 0.32, 0.70 and 0.75 (these were denoted as AvIV, AvIII, AvII and AvI respectively). A hot chloroform extract was partitioned on a silica gel column and the four antifungal compounds were separated. Spectroscopic data revealed that one of these compounds, AvII, was similar to cis-l-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-diene and another (AvIV) was a long chain saturated compound comprising hydroxyl group(s) having molecular weight of 268. Toxicity of AvII to C. gloeosporioides was 2 times that of AvIV and 6.5 and 7.5 times that of AvIII and AvI respectively. The amounts of these four antifungal compounds increased gradually during fruit development and reached their maxima at harvest. The concentration of AvI, AvII, AvIII and AvIV was 1300, 920, 1050 and 780 μg/g fresh peel respectively in the fruit at harvesting maturity. The amount of AvII and AvIV decreased to 53 and 64 μg/g fresh peel respectively in the fruit at the ripe stage at which neither AvI nor AvIII was detected. This took place in coincidence with the onset of progressive lesion development by the fungus.     

Unlinking chromosome catenanes in vivo by site-specific recombination

A challenge for chromosome segregation in all domains of life is the formation of catenated progeny chromosomes, which arise during replication as a consequence of the interwound strands of the DNA double helix. Topoisomerases play a key role in DNA unlinking both during and at the completion of replication. Here we report that chromosome unlinking can instead be accomplished by multiple rounds of site-specific recombination. We show that step-wise, site-specific recombination by XerCD-dif or Cre-loxP can unlink bacterial chromosomes in vivo, in reactions that require KOPS-guided DNA translocation by FtsK. Furthermore, we show that overexpression of a cytoplasmic FtsK derivative is sufficient to allow chromosome unlinking by XerCD-dif recombination when either subunit of TopoIV is inactivated. We conclude that FtsK acts in vivo to simplify chromosomal topology as Xer recombination interconverts monomeric and dimeric chromosomes.     

The FtsK gamma domain directs oriented DNA translocation by interacting with KOPS

The bacterial septum-located DNA translocase FtsK coordinates circular chromosome segregation with cell division. Rapid translocation of DNA by FtsK is directed by 8-base-pair DNA motifs (KOPS), so that newly replicated termini are brought together at the developing septum, thereby facilitating completion of chromosome segregation. Translocase functions reside in three domains, alpha, beta and gamma. FtsKalphabeta are necessary and sufficient for ATP hydrolysis-dependent DNA translocation, which is modulated by FtsKgamma through its interaction with KOPS. By solving the FtsKgamma structure by NMR, we show that gamma is a winged-helix domain. NMR chemical shift mapping localizes the DNA-binding site on the gamma domain. Mutated proteins with substitutions in the FtsKgamma DNA-recognition helix are impaired in DNA binding and KOPS recognition, yet remain competent in DNA translocation and XerCD-dif site-specific recombination, which facilitates the late stages of chromosome segregation.