Results from extensive coarse-grained level molecular dynamics simulations studies of <i>Bacillus subtilis</i> lipase A (LipA) in an oil-water biphasic system both in the presence and absence of Thesit detergent show a bimodal orientational distribution of the enzyme (LipA) at the oil-water interface. This bimodal distribution arises from the ellipsoidal Janus particle-like character of LipA which induces two opposing aspects: Janus-like behaviour (well-partitioning of hydrophobic and hydrophilic parts between oil and aqueous phases) and Pickering effect (maximizing the interfacial area occupied by an emulsifier). Contributions from several energies related to the enzyme at the interface are calculated to quantify the ellipsoidal Janus nanocolloid-like orientational behaviour. Furthermore, we show that the relative orientational preference can be tuned by pH.<br/><br/>Surfactants are used as co-solvent with water not only to offer a less polar environment to the lipases needed for their interfacial activation but also to solvate the substrates which are otherwise poorly soluble in water. Regular MD and umbrella sampling simulations rationalize the experimentally observed 10-fold increase in the turnover rate of this lipase upon its non-covalent tag to a single surfactant molecule at the interface, over its rate in bulk water. The four factors identified from simulations to explain this rare experimental finding are: (i) enhanced free energy of adsorption, (ii) interfacial activation upon adsorption, (iii) reduction in orientational fluctuations and (iv) increased translational diffusion of LipA at the interface, to all of which the Janus character of LipA contributes. The Janus behaviour of LipA also helps to stabilize biphasic emulsion needed for its interfacial catalysis. Furthermore, the 10-fold increase in the turnover rate of this enzyme could be promising for its applications in industrial biocatalysis.

Enzyme behaves like switchable nanocolloid at oil-water interface: 10-fold increase in activity

ACS Spring Meeting 2021

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