Affinity of phosphatidylcholine molecular species for the bovine phosphatidylcholine and phosphatidylinositol transfer proteins. Properties of the sn-1 and sn-2 acyl binding sites

Both the phosphatidylcholine transfer protein (PC-TP) and the phosphatidylinositol transfer protein (PI-TP) act as carriers of phosphatidylcholine (PC) molecules between membranes. To study the structure of the acyl binding sites of these proteins, the affinity of 32 distinct natural and related PC molecular species was determined by using a previously developed fluorometric competition assay. Marked differences in affinity between species were observed with both proteins. Affinity vs lipid hydrophobicity (determined by reverse-phase HPLC) plots displayed a well-defined maximum indicating that the acyl chain hydrophobicity is an important determinant of binding of a phospholipid molecule by these transfer proteins. However, besides the overall lipid hydrophobicity, steric properties of the individual acyl chains contribute considerably to the affinity, and PC-TP and PI-TP respond differently to modifications of the acyl chain structure. The affinity of PC-TP increased steadily with increasing unsaturation of the sn-2 acyl moiety, resulting in high affinity for species containing four and six double bonds in the sn-2 chain, whereas the affinity of PI-TP first increased up to two to three double bonds and then declined. These data, as well as the distinct effects of sn-2 chain double bond position and bromination, indicate that the sn-2 acyl chain binding sites of the two proteins are structurally quite different. The sn-1 acyl binding sites are dissimilar as well, since variation of the length of saturated sn-1 chain affected the affinity differently. The data are discussed in terms of the structural organization of the sn-1 and sn-2 acyl binding sites of PC-TP and PI-TP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biological role and structural mechanism of twinfilin-capping protein interaction

Twinfilin and capping protein (CP) are highly conserved actin-binding proteins that regulate cytoskeletal dynamics in organisms from yeast to mammals. Twinfilin binds actin monomer, while CP binds the barbed end of the actin filament. Remarkably, twinfilin and CP also bind directly to each other, but the mechanism and role of this interaction in actin dynamics are not defined. Here, we found that the binding of twinfilin to CP does not affect the binding of either protein to actin. Furthermore, site-directed mutagenesis studies revealed that the CP-binding site resides in the conserved C-terminal tail region of twinfilin. The solution structure of the twinfilin-CP complex supports these conclusions. In vivo, twinfilin's binding to both CP and actin monomer was found to be necessary for twinfilin's role in actin assembly dynamics, based on genetic studies with mutants that have defined biochemical functions. Our results support a novel model for how sequential interactions between actin monomers, twinfilin, CP, and actin filaments promote cytoskeletal dynamics.     

The role of phadiatop in the screening of respiratory allergy

Phadiatop is a new in vitro screening test for respiratory allergy. This test, based on the RAST procedure, detects in serum, the presence of specific IgE to a mixture of common inhalent allergens. Among 70 patients (26 children and 44 adults) consulting for respiratory syndrome, Phadiatop was positive in 31 cases. There were a good correlation between this new test and skin tests (59% for adults and 92% for children), total IgE (70% for adults and 65% for children) and RAST (93% for adults and 96% for children). Phadiatop, with a specificity of 100%, a sensitivity of 82% (76% for adults and 92% for children) and an efficiency of 90% (86% for adults and 96% for children), is a more accurate test than total IgE and could be an excellent in vitro screening test for respiratory allergy.     

Accuracy and Feasibility of Point-Of-Care White Blood Cell Count and C-Reactive Protein Measurements at the Pediatric Emergency Department

Background

Several point-of-care (POC) tests are available for evaluation of febrile patients, but the data about their performance in acute care setting is sparse. We investigated the analytical accuracy and feasibility of POC tests for white blood cell (WBC) count and C-reactive protein (CRP) at the pediatric emergency department (ED).

Methods

In the first part of the study, HemoCue WBC and Afinion AS100 CRP POC analyzers were compared with laboratory’s routine WBC (Sysmex XE-2100) and CRP (Modular P) analyzers in the hospital central laboratory in 77 and 48 clinical blood samples, respectively. The POC tests were then adopted in use at the pediatric ED. In the second part of the study, we compared WBC and CRP levels measured by POC and routine methods during 171 ED patient visits by 168 febrile children and adolescents. Attending physicians performed POC tests in capillary fingerprick samples.

Results

In parallel measurements in the laboratory both WBC and CRP POC analyzers showed good agreement with the reference methods. In febrile children at the emergency department (median age 2.4 years), physician performed POC determinations in capillary blood gave comparable results with those in venous blood analyzed in the laboratory. The mean difference between POC and reference test result was 1.1 E9/L (95% limits of agreement from -6.5 to 8.8 E9/L) for WBC and -1.2 mg/L (95% limits of agreement from -29.6 to 27.2 mg/L) for CRP.

Conclusions

POC tests are feasible and relatively accurate methods to assess CRP level and WBC count among febrile children at the ED.     

Human liver epigenetic alterations in non-alcoholic steatohepatitis are related to insulin action

Both genetic and lifestyle factors contribute to the risk of non-alcoholic steatohepatitis (NASH). Additionally, epigenetic modifications may also play a key role in the pathogenesis of NASH. We therefore investigated liver DNA methylation, as a marker for epigenetic alterations, in individuals with simple steatosis and NASH, and further tested if these alterations were associated with clinical phenotypes. Liver biopsies obtained from 95 obese individuals (age: 49.5 ± 7.7 years, BMI: 43 ± 5.7 kg/m², type 2 diabetes [T2D]: 35) as a wedge biopsy during a Roux-en-Y gastric bypass operation were investigated. Thirty-four individuals had a normal liver phenotype, 35 had simple steatosis, and 26 had NASH. Genome-wide DNA methylation pattern was analyzed using the Infinium HumanMethylation450 BeadChip. mRNA expression was analyzed from 42 individuals using the HumanHT-12 Expression BeadChip. We identified 1,292 CpG sites representing 677 unique genes differentially methylated in liver of individuals with NASH (q < 0.001), independently of T2D, age, sex, and BMI. Focusing on the top-ranking 30 and another 37 CpG sites mapped to genes enriched in pathways of metabolism (q = 0.0036) and cancer (q = 0.0001) all together, 59 NASH-associated CpG sites correlated with fasting insulin levels independently of age, fasting glucose, or T2D. From these, we identified 30 correlations between DNA methylation and mRNA expression, for example LDHB (r = ?0.45, P = 0.003). We demonstrated that NASH, more than simple steatosis, associates with differential DNA methylation in the human liver. These epigenetic alterations in NASH are linked with insulin metabolism.     

Vitamin A is linked to the expression of the AI-CIII-AIV gene cluster in familial combined hyperlipidemia

There is growing evidence of the capacity of vitamin A to regulate the expression of the genetic region that encodes apolipoproteins (apo) A-I, C-III, and A-IV. This region in turn has been proposed to modulate the expression of hyperlipidemia in the commonest genetic form of dyslipidemia, familial combined hyperlipidemia (FCHL). The hypothesis tested here was whether vitamin A (retinol), by controlling the expression of the AI-CIII-AIV gene cluster, plays a role in modulating the hyperlipidemic phenotype in FCHL. We approached the subject by studying three genetic variants of this region: a C1100-T transition in exon 3 of the apoC-III gene, a G3206-T transversion in exon 4 of the apoC-III gene, and a G-75-A substitution in the promoter region of the apoA-I gene. The association between plasma vitamin A concentrations and differences in the plasma concentrations of apolipoproteins A-I and C-III based on the different genotypes was assessed in 48 FCHL patients and 74 of their normolipidemic relatives. The results indicated that the subjects carrying genetic variants associated with increased concentrations of apoA-I and C-III (C1100-T and G-75-A) also presented increased plasma concentrations of vitamin A. This was only observed among the FCHL patients, which suggested that certain characteristics of these patients contributed to this association. The G3206-T was not associated with changes in either apolipoprotein concentrations or in vitamin A.In summary, we report a relationship between genetically determined elevations of proteins of the AI-CIII-AIV gene cluster and vitamin A in FCHL patients. More studies will be needed to confirm that vitamin A plays a role in FCHL which might also be important for its potential application to therapeutical approaches.     

Germline fitness-based scoring of cancer mutations

A key goal in cancer research is to find the genomic alterations that underlie malignant cells. Genomics has proved successful in identifying somatic variants at a large scale. However, it has become evident that a typical cancer exhibits a heterogenous mutation pattern across samples. Cases where the same alteration is observed repeatedly seem to be the exception rather than the norm. Thus, pinpointing the key alterations (driver mutations) from a background of variations with no direct causal link to cancer (passenger mutations) is difficult. Here we analyze somatic missense mutations from cancer samples and their healthy tissue counterparts (germline mutations) from the viewpoint of germline fitness. We calibrate a scoring system from protein domain alignments to score mutations and their target loci. We show first that this score predicts to a good degree the rate of polymorphism of the observed germline variation. The scoring is then applied to somatic mutations. We show that candidate cancer genes prone to copy number loss harbor mutations with germline fitness effects that are significantly more deleterious than expected by chance. This suggests that missense mutations play a driving role in tumor suppressor genes. Furthermore, these mutations fall preferably onto loci in sequence neighborhoods that are high scoring in terms of germline fitness. In contrast, for somatic mutations in candidate onco genes we do not observe a statistically significant effect. These results help to inform how to exploit germline fitness predictions in discovering new genes and mutations responsible for cancer.     

Screening of microbes for novel acidic cutinases and cloning and expression of an acidic cutinase from Aspergillus niger CBS 513.88

Isolates from gardening waste compost and 38 culture collection microbes were grown on agar plates at pH 4.0 with the cutinase model substrate polycaprolactone as a carbon source. The strains showing polycaprolactone hydrolysis were cultivated in liquid at acidic pH and the cultivations were monitored by assaying the p-nitrophenyl butyrate esterase activities. Culture supernatants of four strains were analyzed for the hydrolysis of tritiated apple cutin at different pHs. Highest amounts of radioactive hydrolysis products were detected at pHs below 5. The hydrolysis of apple cutin by the culture supernatants at acidic pH was further confirmed by GC–MS analysis of the hydrolysis products. On the basis of screening, the acidic cutinase from Aspergillus niger CBS 513.88 was chosen for heterogeneous production in Pichia pastoris and for analysis of the effects of pH on activity and stability. The recombinant enzyme showed activity over a broad range of pHs with maximal activity between pH 5.0 and 6.5. Activity could be detected still at pH 3.5.