Abstract:Cocaine is recognized as the most reinforcing of all drugs of abuse. There is no anticocaine medication available. The disastrous medical and social consequences of cocaine addiction have made the development of an anticocaine medication a high priority. It has been recognized that an ideal anticocaine medication is one that accelerates cocaine metabolism producing biologically inactive metabolites via a route similar to the primary cocaine-metabolizing pathway, i.e., cocaine hydrolysis catalyzed by plasma enzyme butyrylcholinesterase (BChE). However, wild-type BChE has a low catalytic efficiency against the abused cocaine. Design of a high-activity enzyme mutant is extremely challenging, particularly when the chemical reaction process is rate-determining for the enzymatic reaction. Here we report the design and discovery of a high-activity mutant of human BChE by using a novel, systematic computational design approach based on transition-state simulations and activation energy calculations. The novel computational design approach has led to discovery of the most efficient cocaine hydrolase, i.e., a human BChE mutant with an ∼2000-fold improved catalytic efficiency, promising for therapeutic treatment of cocaine overdose and addiction as an exogenous enzyme in human. The encouraging discovery resulted from the computational design not only provides a promising anticocaine medication but also demonstrates that the novel, generally applicable computational design approach is promising for rational enzyme redesign and drug discovery.

Molecular dynamics was used to simulate the transition state for the first chemical reaction step (TS1) of cocaine hydrolysis catalyzed by human butyrylcholinesterase (BChE) and its mutants. The simulated results demonstrate that the overall hydrogen bonding between the carbonyl oxygen of (؊)-cocaine benzoyl ester and the oxyanion hole of BChE in the TS1 structure for (؊)-cocaine hydrolysis catalyzed by A199S͞S287G͞A328W͞Y332G BChE should be significantly stronger than that in the TS1 structure for (؊)-cocaine hydrolysis catalyzed by the WT BChE and other simulated BChE mutants. Thus, the transition-state simulations predict that A199S͞ S287G͞A328W͞Y332G mutant of BChE should have a significantly lower energy barrier for the reaction process and, therefore, a significantly higher catalytic efficiency for (؊)-cocaine hydrolysis. The theoretical prediction has been confirmed by wet experimental tests showing an Ϸ(456 ؎ 41)-fold improved catalytic efficiency of A199S͞S287G͞A328W͞Y332G BChE against (؊)-cocaine. This is a unique study to design an enzyme mutant based on transitionstate simulation. The designed BChE mutant has the highest catalytic efficiency against cocaine of all of the reported BChE mutants, demonstrating that the unique design approach based on transition-state simulation is promising for rational enzyme redesign and drug discovery. molecular dynamics ͉ rational design ͉ transition-state stabilization ͉ cocaine ͉ enzyme-substrate binding C ocaine is recognized as the most reinforcing of all drugs of abuse (1-3). The disastrous medical and social consequences of cocaine addiction have made the development of an effective pharmacological treatment a high priority (4-6). However, cocaine mediates its reinforcing and toxic effects by blocking neurotransmitter reuptake, and the classical pharmacodynamic approach has failed to yield small-molecule receptor antagonists because of the difficulties inherent in blocking a blocker (1-5). An alternative to receptor-based approaches is to interfere with the delivery of cocaine to its receptors or accelerate its metabolism in the body (5,(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). An ideal molecule for this purpose should be a potent enzyme catalyzing the hydrolysis of cocaine into biologically inactive metabolites. The dominant pathway for cocaine metabolism in primates is butyrylcholinesterase (BChE)-catalyzed hydrolysis at the benzoyl ester group (Fig. 3, which is published as supporting information on the PNAS web site), and the metabolites are all biologically inactive (5, 18). Clearly, BChE-catalyzed hydrolysis of cocaine at the benzoyl ester is the metabolic pathway most suitable for amplification. However, the catalytic activity of this plasma enzyme is Ϸ1,000-fold lower against the naturally occurring (Ϫ)-cocaine than that against the biologically inactive (ϩ)-cocaine enantiomer (19)(20)(21)(22). (ϩ)-cocaine can be cleared from plasma in seconds, before partitioning into the CNS, whereas (Ϫ)-cocaine has a plasma half-life of Ϸ45-90 min, long enough for ...

Stretchable conductors are vital and indispensable components in soft electronic systems. The development for stretchable conductors has been highly motivated with different approaches established to address the dilemma in the conductivity and stretchability trade-offs to some extent. Here, a new strategy to achieve superelastic conductors with high conductivity and stable electrical performance under stretching is reported. It is demonstrated that by electrically anchoring conductive fillers with eutectic gallium indium particles (EGaInPs), significant improvement in stretchability and durability can be achieved in stretchable conductors. Different from the strategy of modulating the chemical interactions between the conductive fillers and host polymers, the EGaInPs provide dynamic and robust electrical anchors between the conductive fillers. A superelastic conductor which can achieve a high stretchability with 1000% strain at initial conductivity of 8331 S cm and excellent cycling durability with about eight times resistance change (compared to the initial resistance at 0% strain before stretching) after reversibly stretching to 800% strain for 10 000 times is demonstrated. Applications of the superelastic conductor in an interactive soft touch device and a stretchable light-emitting system are also demonstrated, featuring its promising applications in soft robotics or soft and interactive human-machine interfaces.

morphing, soft architecture, lightweight, and small footprint in the smart and interactive soft robotics. The development of soft actuation technologies mimicking the functionalities of natural muscles is in imperative demand. Despite that challenges still exist to realize muscle-like performances which can be compared to that of the natural muscles in all aspects, artificial muscles have been able to surpass the performance of their natural counterparts in some particular properties. For instance, dielectric elastomer actuators (DEA) are capable of producing strains of >300%; [4] thermal responsive coiled polymer fibers can achieve an impressive specific power of 27.1 kW kg -1 which is 84 times of the peak output power from natural muscle; [5] pressurized fluid actuator can be programmed to transform into complex 3D texture and imitate natural stones and plants; [6] soft magnetic actuators with small feature size can provide multiple locomotive modes of swimming, diving, walking, jumping, and crawling. [7] These latest advancements in the artificial muscles shall be highlighted to inspire approaches and strategies for the future development of artificial muscles.Hitherto, many other interesting mechanisms have also been developed to enable artificial muscles. For example, liquid crystal polymers which change the molecular order under applied stimuli to generate reversible macroscopic actuations, [8][9][10][11][12] chemomechanical actuators which can change shapes in response to chemical stimuli such as humidity, acid, base, and solvent, [13][14][15][16][17][18][19] carbon nanotube (CNT) muscles based on electrochemical reaction or electrostatic force, [20][21][22][23][24] and hydrogel actuators working with osmotic pressure or with incorporated active materials (a review on hydrogel machine has been provided by Liu et al. recently [25] ). Although these devices will not be covered here, more comprehensive reviews summarizing on different kinds of soft actuators can be found in the articles by Madden et al., [3] McCracken et al., [26] Hines et al., [27] and Mirvakili and Hunter. [28] While the initial investigations on artificial muscles have been focused on enabling soft actuators with improved mechanical performances, there is a clear shift in recent years to integrate soft functional electronic devices, including the sensing devices which can perceive external stimulus such as strain, pressure, and temperature etc. and the responding device which can provide interactive feedbacks to the users such as emissive surfaces, color changes, and acoustic outputs etc., to impart mechanical intelligence in the soft actuators. The Artificial muscles are the core components of the smart and interactive soft robotic systems, providing the capabilities in shape morphing, manipulation, and mobility. Intense research efforts in the development of artificial muscles are based on the dielectric elastomer actuators, pneumatic actuators, electrochemical actuators, soft magnetic actuators, and stimulus responsive polymers. Recent ...