Protein engineering provides a means to alter protein structure leading to new functions. Much work has focused on the engineering of enzyme active sites to enhance catalytic activity, however there is an increasing trend towards engineering other aspects of biocatalysts as these efforts can also lead to useful improvements. This tutorial discusses recent advances in engineering an enzyme's local chemical and physical environment, with the goal of enhancing enzyme reaction kinetics, substrate selectivity, and activity in harsh conditions (e.g., low or high pH). By introducing stimuli-responsiveness to these enzyme modifications, dynamic control of activity also becomes possible. These new biomolecular and protein engineering techniques are separate and independent from traditional active site engineering and can therefore be applied synergistically to create new biocatalyst technologies with novel functions.
This work combines the thermostable alcohol dehydrogenase D (AdhD) from Pyrococcus furiosus and the organic electrocatalyst TEMPO to create a bifunctional catalyst that selectively oxidizes primary and secondary alcohols. The active sites function independently, can be switched on by changing reaction conditions, and can selectively oxidize a mixture of 1- and 2-butanol. The NAD-dependent enzyme catalyses the secondary alcohol oxidation at a rate 3-fold faster than the primary alcohol, while the covalently attached 4-glycidyl-TEMPO oxidizes 1-butanol and has negligible activity toward 2-butanol. This hybrid catalytic approach has potential value for selective alcohol oxidations as well as other electrochemical and enzymatic multistep processes in energy conversion and chemical synthesis.
Biological mineralization demonstrates how nature can produce elegant structures through controlled organic–mineral interactions. These organics are often used to control shape, size and orientation of mineral. Inspired from nature, the authors utilize an organic agent, ethylenediamine, as a mineralizer to inhibit rapid hydrolysis and condensation of zinc oxide, and thus control crystal growth behavior. Through adjustment of synthesis parameters, such as precursor concentration and the molar ratio of the inorganic precursor and organic ligands, the authors investigate the mechanism of formation of highly branched zinc oxide nanostructures, which can be used for improving efficiency in energy conversion and water purification applications.
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