Structural insight into the expanded PCB-degrading abilities of a biphenyl dioxygenase obtained by directed evolution

The biphenyl dioxygenase of Burkholderia xenovorans LB400 is a multicomponent Rieske-type oxygenase that catalyzes the dihydroxylation of biphenyl and many polychlorinated biphenyls (PCBs). The structural bases for the substrate specificity of the enzyme's oxygenase component (BphAE_LB400) are largely unknown. BphAE_p4, a variant previously obtained through directed evolution, transforms several chlorobiphenyls, including 2,6-dichlorobiphenyl, more efficiently than BphAE_LB400, yet differs from the parent oxygenase at only two positions: T335A/F336M. Here, we compare the structures of BphAE_LB400 and BphAE_p4 and examine the biochemical properties of two BphAE_LB400 variants with single substitutions, T335A or F336M. Our data show that residue 336 contacts the biphenyl and influences the regiospecificity of the reaction, but does not enhance the enzyme's reactivity toward 2,6-dichlorobiphenyl. By contrast, residue 335 does not contact biphenyl but contributes significantly to expansion of the enzyme's substrate range. Crystal structures indicate that Thr335 imposes constraints through hydrogen bonds and nonbonded contacts to the segment from Val320 to Gln322. These contacts are lost when Thr is replaced by Ala, relieving intramolecular constraints and allowing for significant movement of this segment during binding of 2,6-dichlorobiphenyl, which increases the space available to accommodate the doubly ortho-chlorinated congener 2,6-dichlorobiphenyl. This study provides important insight about how Rieske-type oxygenases can expand substrate range through mutations that increase the plasticity and/or mobility of protein segments lining the catalytic cavity.     

Immunogenicity of nuclear-encoded LTB:ST fusion protein from Escherichia coli expressed in tobacco plants

Enterotoxigenic Escherichia coli (ETEC) is one of the main causative agents of diarrhea in infants and for travelers. Inclusion of a heat-stable (ST) toxin into vaccine formulations is mandatory as most ETEC strains can produce both heat-labile (LT) and ST enterotoxins. In this study, a genetic fusion gene encoding for an LTB:ST protein has been constructed and transferred into tobacco via Agrobacterium tumefaciens-mediated transformation. Transgenic tobacco plants carrying the LTB:ST gene are then subjected to GM1-ELISA revealing that the LTB:ST has assembled into pentamers and displays antigenic determinants from both LTB and ST. Protein accumulation of up to 0.05% total soluble protein is detected. Subsequently, mucosal and systemic humoral responses are elicited in mice orally dosed with transgenic tobacco leaves. This has suggested that the plant-derived LTB:ST is immunogenic via the oral route. These findings are critical for the development of a plant-based vaccine capable of eliciting broader protection against ETEC and targeting both LTB and ST. Features of this platform in comparison to transplastomic approaches are discussed.     

Estrogen receptor alpha (ERS1) SNPs c454-397T>C (PvuII) and c454-351A>G (XbaI) are risk biomarkers for breast cancer development

There are several risk factors related to Breast Cancer (BC) risks and response to chemotherapy with SERMs. Recently some single nucleotide polymorphisms (SNPs) on ESR1 gene have been associated to this disease. However, data are still inconclusive. The present study aimed to investigate the association of SNPs c454-397T>C (also called PvuII) and c454-351A>G (so called XbaI) to incidence of sporadic BC; ERα expression in BC; tamoxifen hormonetherapy (HT-TMX) responsiveness. To do so, a cohort of BC patients was analyzed through retrospective data collection, immunohistochemistry to ERα protein, and genotyping for PvuII and XbaI SNPs by PCR–RFLP, confirmed by sequencing. Significant difference in PvuII alleles frequencies were found BC patients when compared to control samples. Patients with P allele have a 5.14-fold increased BC risk. We found higher P and X alleles frequencies in ERα positive BC and the pp and xx genotypes were observed exclusively in patients with HT-TMX-responsive BC. Taken together, data indicates that P allele as a novel sporadic BC biomarker whereas p and x alleles enhanced chemotherapy responsiveness.     

Winter is coming: Miocene and Quaternary climatic shifts shaped the diversification of Western‐Mediterranean Harpactocrates (Araneae,Dysderidae) spiders

Past climatic shifts have played a major role in generating and shaping biodiversity. Quaternary glacial cycles are the better known examples of dramatic climatic changes endured by ecosystems in temperate regions. Although still a matter of debate, some authors suggest that glaciations promoted speciation. Here we investigate the effect of past climatic changes on the diversification of the ground‐dwelling spider genus Harpactocrates, distributed across the major mountain ranges of the western Mediterranean. Concatenated and species‐tree analyses of multiple mitochondrial and nuclear loci, combined with the use of fossil and biogeographic calibration points, reveal a Miocene origin of most nominal species, but also unravel several cryptic lineages tracing back to the Pleistocene. We hypothesize that the Miocene Climatic Transition triggered major extinction events in the genus but also promoted its subsequent diversification. Under this scenario, the Iberian mountains acted as an island‐like system, providing shelter to Harpactocrates lineages during the climate shifts and favouring isolation between mountain ranges. Quaternary glacial cycles contributed further to the diversification of the group by isolating lineages in peripheral refugia within mountain ranges. In addition, we recovered some unique biogeographic patterns, such as the colonization of the Alps and the Apennines from the Iberian Peninsula.     

FEV1 inversely correlates with metalloproteinases 1, 7, 9 and CRP in COPD by biomass smoke exposure

Background

Matrix metalloproteinases (MMPs) and C-reactive protein (CRP) are involved in chronic obstructive pulmonary disease (COPD) pathogenesis. The aim of the present work was to determine plasma concentrations of MMPs and CRP in COPD associated to biomass combustion exposure (BE) and tobacco smoking (TS).

Methods

Pulmonary function tests, plasma levels of MMP-1, MMP-7, MMP-9, MMP-9/TIMP-1 and CRP were measured in COPD associated to BE (n = 40) and TS (n =40) patients, and healthy non-smoking (NS) healthy women (controls, n = 40).

Results

Plasma levels of MMP-1, MMP-7, MMP-9, and MMP-9/TIMP-1 and CRP were higher in BE and TS than in the NS healthy women (p <0.01). An inverse correlation between MMP-1, MMP-7, MMP-9, MMP-9/TIMP-1 and CRP plasma concentrations and FEV₁ was observed.

Conclusions

Increase of MMPs and CRP plasma concentrations in BE suggests a systemic inflammatory phenomenon similar to that observed in COPD associated to tobacco smoking, which may also play a role in COPD pathogenesis.