Enzymes as nanocatalysts: Classical catalysis has been accused of relying mainly on trial-and-error methods. The nascent field of nanocatalysis aims to control chemical reactions by changing the size, shape, chemical composition and morphology of the catalyst, for the purpose of driving the kinetics towards the desired reaction product. This approach opens up new avenues for atom-by-atom design of nanocatalysts with distinct and tunable chemical activity, specificity and selectivity. However, this discipline is highly focused on inorganic catalysts (typically expensive and pollutant rare-earths or precious metals) still with an emphasis on trial-and-error iterations.
By contrast, enzymes (a specific type of proteins) are nanometer-sized bioorganic catalysts refined by millions of years of evolution (i.e. a massive number of trial-and-error iterations inherent in natural selection), such that some of them are considered “catalytically perfect” (i.e. their specificity constant, kcat/KM, approaches the limit of diffusion: 108-109 M-1s-1). Thus, enzymes are ready-to-go nanomachines that provide efficient nanocatalysis and serve as the ideal starting point from which to set out on rational design for industrial applications.
Advantages of bio-inspired nanocatalysts: There are many advantages in using enzymes as nanocatalysts in industry. First, they are ideal catalysts with extremely high activity, selectivity and specificity. Second, the control of the particle size is extremely precise and reproducible, resulting in a very homogeneous population of nanocatalysts. Achieving homogeneity in particle size is one of the challenges in nanocatalysis. Third, they can be produced and re-engineered very precisely, easily and cheaply by established biotechnological processes (including site-directed mutagenesis, protein engineering and directed evolution) to make them more suitable for industrial applications. Fourth, they can be inactivated (by denaturation, cross-linking or hydrolysis) and are biodegradable, which further reduces their already minor environmental impact and makes them extremely safe.
A natural cellulosome design. One of the many architectures of the cellulosome, a self-assembled enzymatic complex evolved for efficient lignocellulose degradation. CBM: carbohydrate-binding module.
The cellulosome as an efficient nanocatalyst: Life is based on the nanoworld, mainly the world of protein molecules (made from information encoded in DNA) that recognize and bind other molecules. Many complex biological processes are catalyzed by self-assembled cascades of multiple enzymes in a coordinated manner. To this end, organisms have developed protein scaffolds that anchor the corresponding enzymes in solid-phase so that their activities can be spatio-temporally coordinated. Not surprisingly, these scaffolding proteins are increasingly attracting the attention from scientists. In particular, “scaffoldin” coordinates a variety of polysaccharide-degrading enzymes into a highly polymorphic complex called the cellulosome. This multi-enzyme complex has been shown to be much more efficient in degrading plant cell wall derived polysaccharides than the sum of the component enzymes alone.
More information in CellulosomePlus Project (EU 7FP NMP.2013.1.1-2. GA nº 604530).