ITQB: MET - PhD Theses
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- Exploring Strategies for Improved Catalytic Efficiency and Thermal Stabilisation of DyP-type Peroxidases using Protein EngineeringPublication . Rodrigues, Carolina Ferro; Oliveira Martins, Lígia"Dye-decolorizing Peroxidases (DyPs) are a relatively new family of microbial heme-containing peroxidases, from both fungal and bacterial sources. They display a a+b ferredoxin-like fold, and a carboxylate residue as an acid-base catalyst, in contrast to the conserved histidine found in classical peroxidases. The heme cofactor is non-covalently bound and coordinated by a proximal axial histidine ligand. Although their physiological role remains in debate, they are capable of oxidising a wide range of substrates, including synthetic dyes, metals, as well as phenolic and non-phenolic lignin-related compounds, which contribute to their biotechnological potential in lignocellulose biorefineries.(...)"
- New Bacterial Carbohydrate Oxidases: Structure-Function Insights and Biotechnological ApplicationsPublication . Teixeira Taborda, André Filipe; Martins, Lígia"Plant biomass is an abundant and renewable source of carbohydrates which act as substrates for microbial growth and ecosystem transformation. To access and modify these complex molecules, microorganisms have evolved specialized enzymatic systems, such as carbohydrate oxidases, capable of highly specific and selective reactions. These oxidoreductases promote the regioselective oxidation of hydroxyl groups, utilizing molecular oxygen as an electron acceptor, and produce hydrogen peroxide as a byproduct.(...)"
- Improvement of Isoeugenol Dioxygenases for the Sustainable Production of Lignin-derived VanillinPublication . De Simone, Mario; Martins, Lígia Oliveira"Lignocellulose is the main component of all plant materials, primarily composed of three biopolymers: lignin, cellulose, and hemicellulose. While cellulose and hemicellulose are widely used as renewable sources, lignin often remains a low-value by-product despite being the most abundant source of phenolics. All lignocellulose components, including lignin, must be fully valorized to make the biorefinery concept feasible and sustainable. Lignin can be transformed into value-added products, including vanillin, the most used flavor and fragrance globally.(...)."
- A Closer Look at a Potential Biocatalyst: Unravelling the Catalytic, Stability and Structural Features of PpDyP, a DyP-type PeroxidasePublication . Ribeiro da Silva, Diogo André; Martins, LígiaLignin is the largest reserve of aromatics on Earth and is a key renewable source of chemicals and materials; however, it remains mostly unexplored due to its recalcitrance to degradation. Recently, new state-of-the-art methods have been developed to depolymerize lignin and generate a portfolio of well-defined, industrial-relevant compounds, however, a lot of work remains to be done on the transformation of these compounds.
- Towards Cooperative Organometallic and Enzymatic Catalysis to Develop New Value Chains from Organic WastesPublication . Fernandes, Ana Elisabete da Silva; Martins, Lígia O.; Royo, Beatriz"The procurement of sustainable technologies is the major driving force for current industrial development. The 12 principles of Green Chemistry are important guidelines for their development and the first one directs towards waste reduction instead of remediation. (...)"
- Multi-Enzymatic Systems for Cleaning-up Synthetic Dyes from the EnvironmentPublication . Mendes, Sónia Alexandra Gonçalves; Martins, LígiaEnvironmental pollution is one of the major and most important problems of the modern world. In order to fulfill the needs and demands of the overgrowing human population, developments in agriculture, medicine, energy sources, and all chemical industries are necessary (Ali 2010). Over the last century, the increased industrialization and continued population growth led to an augmented production of environmental pollutants that are released into air, water, and soil, with significant impact in the degradation of various ecosystems (Ali 2010, Khan et al. 2013).(...)
- Insight into the multicopper oxidases stabilityPublication . Fernandes, André João Tavares; Martins, Lígia O.; Melo, Eduardo P.This dissertation portrays recent development on the knowledge of the stability determinants and of functional characteristics of multicopper oxidases (MCO). Multicopper oxidases are a family of enzymes that includes laccases (benzenediol oxygen oxidoreductase; EC 1.10.3.2), ascorbate oxidase (L-ascorbate oxygen oxidoreductase, EC 1.10.3.3) and ceruloplasmin (Fe2+ oxygen oxidoreductase, EC 1.16.3.1). MCO are characterized by having four copper ions that are classified into three distinct types of copper sites, namely type 1 (T1), type 2 (T2) and type 3 (T3). The classical T1 copper site comprises two histidine residues and a cysteine residue arranged in a distorted trigonal geometry around the copper ion with bonding distances approx. 2.0 Å (1 Å=0.1 nm); a weaker fourth methionine ligand completes the tetrahedral geometry. The copper–cysteine linkage is characterized by an intense S(π)→Cu(dx2−y2) CT (charge transfer) absorption band at approximately 600 nm, and a narrow parallel hyperfine splitting A\\ = (43–90)×10−4 cm−1 in the electron paramagnetic resonance (EPR) spectrum. The function of the T1 copper site is to shuttle electrons from substrates to the trinuclear copper centre where molecular oxygen is reduced to two molecules of water during the complete four-electron catalytic cycle. The trinuclear center contains a T2 copper coordinated by two histidine residues and one water molecule, lacks strong absorption bands and exhibits a large parallel hyperfine splitting in the EPR spectrum (A\\ = (150–201)×10−4 cm−1). The T2 copper site is in close proximity to two T3 copper ions, which are each coordinated by three histidine residues and typically coupled, for example, through a dioxygen molecule. The T3 or coupled binuclear copper site is characterized by an intense absorption band at 330 nm originating from the bridging ligand and by the absence of an EPR signal due to the antiferromagnetically coupling of the copper ions.(...)