Unfolding pathway of CotA-laccase and the role of copper on the prevention of refolding through aggregation of the unfolded state.

Copper is a redox-active metal and the main player in electron transfer reactions occurring in multicopper oxidases. The role of copper in the unfolding pathway and refolding of the multicopper oxidase CotA laccase in vitro was solved using double-jump stopped-flow experiments. Unfolding of apo- and holo-CotA was described as a three-state process with accumulation of an intermediate in between the native and unfolded state. Copper stabilizes the native holo-CotA but also the intermediate state showing that copper is still bound to this state. Also, copper binds to unfolded holo-CotA in a non-native coordination promoting CotA aggregation and preventing refolding to the native structure. These results gather information on unfolding/folding pathways of multicopper oxidases and show that copper incorporation in vivo should be a tight controlled process as copper binding to the unfolded state under native conditions promotes protein aggregation.

The removal of a disulfide bridge in CotA-laccase changes the slower motion dynamics involved in copper binding but has no effect on the thermodynamic stability.

The contribution of the disulfide bridge in CotA-laccase from Bacillus subtilis is assessed with respect to the enzyme's functional and structural properties. The removal of the disulfide bond by site-directed mutagenesis, creating the C322A mutant, does not affect the spectroscopic or catalytic properties and, surprisingly, neither the long-term nor the thermodynamic stability parameters of the enzyme. Furthermore, the crystal structure of the C322A mutant indicates that the overall structure is essentially the same as that of the wild type, with only slight alterations evident in the immediate proximity of the mutation. In the mutant enzyme, the loop containing the C322 residue becomes less ordered, suggesting perturbations to the substrate binding pocket. Despite the wild type and the C322A mutant showing similar thermodynamic stability in equilibrium, the holo or apo forms of the mutant unfold at faster rates than the wild-type enzyme. The picosecond to nanosecond time range dynamics of the mutant enzyme was not affected as shown by acrylamide collisional fluorescence quenching analysis. Interestingly, copper uptake or copper release as measured by the stopped-flow technique also occurs more rapidly in the C322A mutant than in the wild-type enzyme. Overall the structural and kinetic data presented here suggest that the disulfide bridge in CotA-laccase contributes to the conformational dynamics of the protein on the microsecond to millisecond timescale, with implications for the rates of copper incorporation into and release from the catalytic centres.

The multicopper oxidase from the archaeon Pyrobaculum aerophilum shows nitrous oxide reductase activity.

The multicopper oxidase from the hyperthermophilic archaeon Pyrobaculum aerophilum (McoP) was overproduced in Escherichia coli and purified to homogeneity. The enzyme consists of a single 49.6 kDa subunit, and the combined results of UV-visible, CD, EPR and resonance Raman spectroscopies showed the characteristic features of the multicopper oxidases. Analysis of the McoP sequence allowed its structure to be derived by comparative modeling methods. This model provided a criterion for designing meaningful site-directed mutants of the enzyme. McoP is a hyperthermoactive and thermostable enzyme with an optimum reaction temperature of 85 degrees C, a half-life of inactivation of approximately 6 h at 80 degrees C, and temperature values at the midpoint from 97 to 112 degrees C. McoP is an efficient metallo-oxidase that catalyzes the oxidation of cuprous and ferrous ions with turnover rate constants of 356 and 128 min(-1), respectively, at 40 degrees C. It is noteworthy that McoP follows a ping-pong mechanism, with three-fold higher catalytic efficiency when using nitrous oxide as electron acceptor than when using dioxygen, the typical oxidizing substrate of multicopper oxidases. This finding led us to propose that McoP represents a novel archaeal nitrous oxide reductase that is most probably involved in the final step of the denitrification pathway of P. aerophilum.

Vaccinia virus infection in monkeys, Brazilian Amazon.

To detect orthopoxvirus in the Brazilian Amazon, we conducted a serosurvey of 344 wild animals. Neutralizing antibodies against orthopoxvirus were detected by plaque-reduction neutralizing tests in 84 serum samples. Amplicons from 6 monkey samples were sequenced. These amplicons identified vaccinia virus genetically similar to strains from bovine vaccinia outbreaks in Brazil.

Human Vaccinia virus and Pseudocowpox virus co-infection: clinical description and phylogenetic characterization.

BACKGROUND: Occupational exanthematic diseases represent an important cause of public health impact and economical losses. Among the viral exanthematic diseases, two caused by poxviruses are noteworthy: the bovine vaccinia (BV), caused by the Vaccinia virus (VACV); and the milker's nodule, in which the agent is the Pseudocowpox virus (PCPV). Both agents are zoonotic and have been associated with several cases of bovine infection. In Brazilian rural areas BV has been highly prevalent, particularly in milk herds. Farmers, milkers and their close contacts developed lesions on the hands, forearms, legs and face accompanied by several systemic symptoms. Although VACV and PCPV present with similar epidemiological and transmission patterns, no VACV and PCPV co-infection cases have to date been described. OBJECTIVES: To describe the first case of zoonotic VACV and PCVP co-infection, based on serological and molecular methods. STUDY DESIGN AND RESULTS: In this work we report a case of a Brazilian rural worker who presented with a large severely ulcerated-pustule skin lesion, associated with fever, headache, malaise, myalgia and axillary, inguinal and cervical limphadenopathy. The worker declared occupational contact with cattle that had notable injuries on their teats. Human and bovine clinical samples were collected and submitted to serological and molecular tests. PCR and phylogenetic analysis revealed the presence of VACV DNA and PCPV DNA in the patient's lesion. Serological tests indicated anti-VACV neutralizing antibodies and molecular assays showed the presence of VACV and PCPV DNA in the patient sera. VACV and PCPV also were detected in dairy cattle. CONCLUSION: Together, these results indicate a case of zoonotic VACV/PCPV co-infection. Epidemiological surveillance and appropriate medical treatment are essential for the control of both diseases, especially in the most severe cases, as described in the present study.

One more piece in the VACV ecological puzzle: could peridomestic rodents be the link between wildlife and bovine vaccinia outbreaks in Brazil?

BACKGROUND: Despite the fact that smallpox eradication was declared by the World Health Organization (WHO) in 1980, other poxviruses have emerged and re-emerged, with significant public health and economic impacts. Vaccinia virus (VACV), a poxvirus used during the WHO smallpox vaccination campaign, has been involved in zoonotic infections in Brazilian rural areas (Bovine Vaccinia outbreaks - BV), affecting dairy cattle and milkers. Little is known about VACV's natural hosts and its epidemiological and ecological characteristics. Although VACV was isolated and/or serologically detected in Brazilian wild animals, the link between wildlife and farms has not yet been elucidated. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we describe for the first time, to our knowledge, the isolation of a VACV (Mariana virus - MARV) from a mouse during a BV outbreak. Genetic data, in association with biological assays, showed that this isolate was the same etiological agent causing exanthematic lesions observed in the cattle and human inhabitants of a particular BV-affected area. Phylogenetic analysis grouped MARV with other VACV isolated during BV outbreaks. CONCLUSION/SIGNIFICANCE: These data provide new biological and epidemiological information on VACV and lead to an interesting question: could peridomestic rodents be the link between wildlife and BV outbreaks?

Nested-multiplex PCR detection of Orthopoxvirus and Parapoxvirus directly from exanthematic clinical samples.

BACKGROUND: Orthopoxvirus (OPV) and Parapoxvirus (PPV) have been associated with worldwide exanthematic outbreaks. Some species of these genera are able to infect humans and domestic animals, causing serious economic losses and public health impact. Rapid, useful and highly specific methods are required to detect and epidemiologically monitor such poxviruses. In the present paper, we describe the development of a nested-multiplex PCR method for the simultaneous detection of OPV and PPV species directly from exanthematic lesions, with no previous viral isolation or DNA extraction. METHODS AND RESULTS: The OPV/PPV nested-multiplex PCR was developed based on the evaluation and combination of published primer sets, and was applied to the detection of the target pathogens. The method showed high sensitivity, and the specificity was confirmed by amplicon sequencing. Exanthematic lesion samples collected during bovine vaccinia or contagious ecthyma outbreaks were submitted to OPV/PPV nested-multiplex PCR and confirmed its applicability. CONCLUSION: These results suggest that the presented multiplex PCR provides a highly robust and sensitive method to detect OPV and PPV directly from clinical samples. The method can be used for viral identification and monitoring, especially in areas where OPV and PPV co-circulate.

The hyperthermophilic nature of the metallo-oxidase from Aquifex aeolicus.

The stability of the Aquifex aeolicus multicopper oxidase (McoA) was studied by spectroscopy, calorimetry and chromatography to understand its thermophilic nature. The enzyme is hyperthermostable as deconvolution of the differential scanning calorimetry trace shows that thermal unfolding is characterized by temperature values at the mid-point of 105, 110 and 114 degrees C. Chemical denaturation revealed however a very low stability at room temperature (2.8 kcal/mol) because copper bleaching/depletion occur before the unfolding of the tertiary structure and McoA is highly prone to aggregate. Indeed, unfolding kinetics measured with the stopped-flow technique quantified the stabilizing effect of copper on McoA (1.5 kcal/mol) and revealed quite an uncommon observation further confirmed by light scattering and gel filtration chromatography: McoA aggregates in the presence of guanidinium hydrochloride, i.e., under unfolding conditions. The aggregation process results from the accumulation of a quasi-native state of McoA that binds to ANS and is the main determinant of the stability curve of McoA. Kinetic partitioning between aggregation and unfolding leads to a very low heat capacity change and determines a flat dependence of stability on temperature.

Copper incorporation into recombinant CotA laccase from Bacillus subtilis: characterization of fully copper loaded enzymes.

The copper content of recombinant CotA laccase from Bacillus subtilis produced by Escherichia coli cells is shown to be strongly dependent on the presence of copper and oxygen in the culture media. In copper-supplemented media, a switch from aerobic to microaerobic conditions leads to the synthesis of a recombinant holoenzyme, while the maintenance of aerobic conditions results in the synthesis of a copper-depleted population of proteins. Strikingly, cells grown under microaerobic conditions accumulate up to 80-fold more copper than aerobically grown cells. In vitro copper incorporation into apoenzymes was monitored by optical and electron paramagnetic resonance (EPR) spectroscopy. This analysis reveals that copper incorporation into CotA laccase is a sequential process, with the type 1 copper center being the first to be reconstituted, followed by the type 2 and the type 3 copper centers. The copper reconstitution of holoCotA derivatives depleted in vitro with EDTA results in the complete recovery of the native conformation as monitored by spectroscopic, kinetic and thermal stability analysis. However, the reconstitution of copper to apo forms produced in cultures under aerobic and copper-deficient conditions resulted in incomplete recovery of biochemical properties of the holoenzyme. EPR and resonance Raman data indicate that, presumably, folding in the presence of copper is indispensable for the correct structure of the trinuclear copper-containing site.

A robust metallo-oxidase from the hyperthermophilic bacterium Aquifex aeolicus.

The gene, Aquifex aeolicus AAC07157.1, encoding a multicopper oxidase (McoA) and localized in the genome as part of a putative copper-resistance determinant, has been cloned, over-expressed in Escherichia coli and the recombinant enzyme purified to homogeneity. The purified enzyme shows spectroscopic and biochemical characteristics typical of the well-characterized multicopper oxidase family of enzymes. McoA presents higher specificity (k(cat)/K(m)) for cuprous and ferrous ions than for aromatic substrates and is therefore designated as a metallo-oxidase. Addition of copper is required for maximal catalytic efficiency. A comparative model structure of McoA has been constructed and a striking structural feature is the presence of a methionine-rich region (residues 321-363), reminiscent of those found in copper homeostasis proteins. The kinetic properties of a mutant enzyme, McoADeltaP321-V363, deleted in the methionine-rich region, provide evidence for the key role of this region in the modulation of the catalytic mechanism. McoA has an optimal temperature of 75 degrees C and presents remarkable heat stability at 80 and 90 degrees C, with activity lasting for up to 9 and 5 h, respectively. McoA probably contributes to copper and iron homeostasis in A. aeolicus.

Perturbations of the T1 copper site in the CotA laccase from Bacillus subtilis: structural, biochemical, enzymatic and stability studies.

Site-directed mutagenesis has been used to replace Met502 in CotA laccase by the residues leucine and phenylalanine. X-ray structural comparison of M502L and M502F mutants with the wild-type CotA shows that the geometry of the T1 copper site is maintained as well as the overall fold of the proteins. The replacement of the weak so-called axial ligand of the T1 site leads to an increase in the redox potential by approximately 100 mV relative to that of the wild-type enzyme (E0 =455 mV). However the M502L mutant exhibits a twofold to fourfold decrease in the kcat values for the all substrates tested and the catalytic activity in M502F is even more severely compromised; 10% activity and 0.15-0.05% for the non-phenolic substrates and for the phenolic substrates tested when compared with the wild-type enzyme. T1 copper depletion is a key event in the inactivation and thus it is a determinant of the thermodynamic stability of wild-type and mutant proteins. Whilst the unfolding of the tertiary structure in the wild-type enzyme is a two-state process displaying a midpoint at a guanidinium hydrochloride concentration of 4.6 M and a free-energy exchange in water of 10 kcal/mol, the unfolding for both mutant enzymes is clearly not a two-state process. At 1.9 M guanidinium hydrochloride, half of the molecules are in an intermediate conformation, only slightly less stable than the native state (approximately 1.4 kcal/mol). The T1 copper centre clearly plays a key role, from the structural, catalytic and stability viewpoints, in the regulation of CotA laccase activity.