The colors of peroxygenase activity: Colorimetric high-throughput screening assays for directed evolution

Fungal unspecific peroxygenases (UPOs) are arising as versatile biocatalysts for C-H oxyfunctionalization reactions. In recent years, several directed evolution studies have been conducted to design improved UPO variants. An essential part of this protein engineering strategy is the design of reliable colorimetric high-throughput screening (HTS) assays for mutant library exploration. Here, we present a palette of 12 colorimetric HTS assays along with their step-by-step protocols, which have been validated for directed UPO evolution campaigns. This array of colorimetric assays will pave the way for the discovery and design of new UPO variants.

Design of a biocatalytic cascade for the enzymatic sulfation of unsulfated chondroitin with in situ generation of PAPS

Sulfation of molecules in living organisms is a process that plays a key role in their functionality. In mammals, the sulfation of polysaccharides (glycosaminoglycans) that form the proteoglycans present in the extracellular matrix is particularly important. These polysaccharides, through their degree and sulfation pattern, are involved in a variety of biological events as signal modulators in communication processes between the cell and its environment. Because of this great biological importance, there is a growing interest in the development of efficient and sustainable sulfation processes, such as those based on the use of sulfotransferase enzymes. These enzymes have the disadvantage of being 3'-phosphoadenosine 5'-phosphosulfate (PAPS) dependent, which is expensive and difficult to obtain. In the present study, a modular multienzyme system was developed to allow the in situ synthesis of PAPS and its coupling to a chondroitin sulfation system. For this purpose, the bifunctional enzyme PAPS synthase 1 (PAPSS1) from Homo sapiens, which contains the ATP sulfurylase and APS kinase activities in a single protein, and the enzyme chondroitin 4-O-sulfotransferase (C4ST-1) from Rattus norvegicus were overexpressed in E. coli. The product formed after coupling of the PAPS generation system and the chondroitin sulfation module was analyzed by NMR.

Design and biocatalytic applications of genetically fused multifunctional enzymes

Fusion proteins, understood as those created by joining two or more genes that originally encoded independent proteins, have numerous applications in biotechnology, from analytical methods to metabolic engineering. The use of fusion enzymes in biocatalysis may be even more interesting due to the physical connection of enzymes catalyzing successive reactions into covalently linked complexes. The proximity of the active sites of two enzymes in multi-enzyme complexes can make a significant contribution to the catalytic efficiency of the reaction. However, the physical proximity of the active sites does not guarantee this result. Other aspects, such as the nature and length of the linker used for the fusion or the order in which the enzymes are fused, must be considered and optimized to achieve the expected increase in catalytic efficiency. In this review, we will relate the new advances in the design, creation, and use of fused enzymes with those achieved in biocatalysis over the past 20 years. Thus, we will discuss some examples of genetically fused enzymes and their application in carbon‑carbon bond formation and oxidative reactions, generation of chiral amines, synthesis of carbohydrates, biodegradation of plant biomass and plastics, and in the preparation of other high-value products.

Heparanized chitosans: towards the third generation of chitinous biomaterials

The functionalization of chitosans is an emerging research area in the design of solutions for a wide range of biomedical applications. In particular, the modification of chitosans to incorporate sulfate groups has generated great interest since they show structural similarity to heparin and heparan sulfates. Most of the biomedical applications of heparan sulfates are derived from their ability to bind different growth factors and other proteins, as through these interactions they can modulate the cellular response. This review aims to summarize the most recent advances in the synthesis, and structural and physicochemical characterization of heparanized chitosan, a remarkably interesting family of polysaccharides that have demonstrated the ability to mimic heparan sulfates as ligands for different proteins, thereby exerting their biological activity by mimicking the function of these glycosaminoglycans.

Unraveling the Structural Landscape of Chitosan-Based Heparan Sulfate Mimics Binding to Growth Factors: Deciphering Structural Determinants for Optimal Activity

Chitosan sulfates have demonstrated the ability to mimic heparan sulfate (HS) function. In this context, it is crucial to understand how the specific structural properties of HS domains determine their functionalities and biological activities. In this study, several HS-mimicking chitosans have been prepared to mimic the structure of HS domains that have proved to be functionally significant in cell processes. The results presented herein are in concordance with the hypothesis that sulfated chitosan-growth factor (GF) interactions are controlled by a combination of two effects: the electrostatic interactions and the conformational adaptation of the polysaccharide. Thus, we found that highly charged O-sulfated S-CS and S-DCS polysaccharides with a low degree of contraction interacted more strongly with GFs than N-sulfated N-DCS, with a higher degree of contraction and a low charge. Finally, the evidence gathered suggests that N-DCS would be able to bind to an allosteric zone and is likely to enhance GF signaling activity. This is because the bound protein remains able to bind to its cognate receptor, promoting an effect on cell proliferation as has been shown for PC12 cells. However, S-CS and S-DCS would sequester the protein, decreasing the GF signaling activity by depleting the protein or locally blocking its active site.