Improved Production and Biophysical Analysis of Recombinant Silicatein-α

Understanding Biomineralization Mechanisms to Produce Size-Controlled, Tailored Nanocrystals for Optoelectronic and Catalytic Applications: A Review

Biomineralization, the use of biological systems to produce inorganic materials, has recently become an attractive approach for the sustainable manufacturing of functional nanomaterials. Relying on proteins or other biomolecules, biomineralization occurs under ambient temperatures and pressures, which presents an easily scalable, economical, and environmentally friendly method for nanoparticle synthesis. Biomineralized nanocrystals are quickly approaching a quality applicable for catalytic and optoelectronic applications, replacing materials synthesized using expensive traditional routes. Here, we review the current state of development for producing functional nanocrystals using biomineralization and distill the wide variety of biosynthetic pathways into two main approaches: templating and catalysis. Throughout, we compare and contrast biomineralization and traditional syntheses, highlighting optimizations from traditional syntheses that can be implemented to improve biomineralized nanocrystal properties such as size and morphology, making them competitive with chemically synthesized state-of-the-art functional nanomaterials.

Evaluation of Fluorescence-Based Screening Assays for the Detection and Quantification of Silyl Hydrolase Activity

This study reports the development of fluorometric assays for the detection and quantification of silyl hydrolase activity using silicatein as a model enzyme. These assays employed a series of organosilane substrates containing either mycophenolate or umbelliferone moieties, which become fluorescent upon hydrolysis of a scissile Si-O bond. Among these substrates, the mycophenolate-derived molecule MycoF, emerged as the most promising candidate due to its relative stability in aqueous media, which resulted in good differentiation between the enzyme-catalyzed and uncatalyzed background hydrolysis. The utility of MycoF was also demonstrated in the detection of enzyme activity in cell lysates and was found to be capable of qualitative identification of positive "hit" candidates in a high-throughput format. These fluorogenic substrates were also suitable for use in quantitative kinetic assays, as demonstrated by the acquisition of their Michaelis-Menten parameters.

SilE-R and SilE-S-DABB Proteins Catalying Enantiospecific Hydrolysis of Organosilyl Ethers

Silyl ethers fulfil a fundamental role in synthetic organic chemistry as protecting groups and their selective cleavage is an important factor in their application. We present here for the first time two enzymes, SilE-R and SilE-S, which are able to hydrolyse silyl ethers. They belong to the stress-response dimeric A/B barrel domain (DABB) family and are able to cleave the Si-O bond with opposite enantiopreference. Silyl ethers containing aromatic, cyclic or aliphatic alcohols and, depending on the alcohol moiety, silyl functions as large as TBDMS are accepted. The X-ray crystal structure of SilE-R, determined to a resolution of 1.98 Å, in combination with mutational studies, revealed an active site featuring two histidine residues, H8 and H79, which likely act synergistically as nucleophile and Brønsted base in the hydrolytic mechanism, which has not previously been described for enzymes. Although the natural function of SilE-R and SilE-S is unknown, we propose that these 'silyl etherases' may have significant potential for synthetic applications.

Development of Improved Spectrophotometric Assays for Biocatalytic Silyl Ether Hydrolysis

Reported herein is the development of assays for the spectrophotometric quantification of biocatalytic silicon-oxygen bond hydrolysis. Central to these assays are a series of chromogenic substrates that release highly absorbing phenoxy anions upon cleavage of the sessile bond. These substrates were tested with silicatein, an enzyme from a marine sponge that is known to catalyse the hydrolysis and condensation of silyl ethers. It was found that, of the substrates tested, tert-butyldimethyl(2-methyl-4-nitrophenoxy)silane provided the best assay performance, as evidenced by the highest ratio of enzyme catalysed reaction rate compared with the background (uncatalysed) reaction. These substrates were also found to be suitable for detailed enzyme kinetics measurements, as demonstrated by their use to determine the Michaelis-Menten kinetic parameters for silicatein.

Inorganic Polymeric Materials for Injured Tissue Repair: Biocatalytic Formation and Exploitation

Two biocatalytically produced inorganic biomaterials show great potential for use in regenerative medicine but also other medical applications: bio-silica and bio-polyphosphate (bio-polyP or polyP). Biosilica is synthesized by a group of enzymes called silicateins, which mediate the formation of amorphous hydrated silica from monomeric precursors. The polymeric silicic acid formed by these enzymes, which have been cloned from various siliceous sponge species, then undergoes a maturation process to form a solid biosilica material. The second biomaterial, polyP, has the extraordinary property that it not only has morphogenetic activity similar to biosilica, i.e., can induce cell differentiation through specific gene expression, but also provides metabolic energy through enzymatic cleavage of its high-energy phosphoanhydride bonds. This reaction is catalyzed by alkaline phosphatase, a ubiquitous enzyme that, in combination with adenylate kinase, forms adenosine triphosphate (ATP) from polyP. This article attempts to highlight the biomedical importance of the inorganic polymeric materials biosilica and polyP as well as the enzymes silicatein and alkaline phosphatase, which are involved in their metabolism or mediate their biological activity.

Biocatalytic Silylation: The Condensation of Phenols and Alcohols with Triethylsilanol

Silicatein-α (Silα), a hydrolytic enzyme derived from siliceous marine sponges, is one of the few enzymes in nature capable of catalysing the metathesis of silicon–oxygen bonds. It is therefore of interest as a possible biocatalyst for the synthesis of organosiloxanes. To further investigate the substrate scope of this enzyme, a series of condensation reactions with a variety of phenols and aliphatic alcohols were carried out. In general, it was observed that Silα demonstrated a preference for phenols, though the conversions were relatively modest in most cases. In the two pairs of chiral alcohols that were investigated, it was found that the enzyme displayed a preference for the silylation of the S-enantiomers. Additionally, the enzyme’s tolerance to a range of solvents was tested. Silα had the highest level of substrate conversion in the nonpolar solvents n-octane and toluene, although the inclusion of up to 20% of 1,4-dioxane was tolerated. These results suggest that Silα is a potential candidate for directed evolution toward future application as a robust and selective biocatalyst for organosiloxane chemistry.