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Nanoparticle Size Influences Localized Enzymatic Enhancement-A Case Study with Phosphotriesterase

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Enhancements in enzymatic catalytic activity are frequently observed when an enzyme is displayed on a nanoparticle NP surface. The exact mechanisms of how this unique interfacial environment gives rise to this phenomenon are still not understood, although evidence suggests that it can help alleviate some of the enzymes rate-limiting mechanistic steps. The physicochemical limitations that govern when this process arises are also not known including, in particular, the range of NP size and curvature that are associated with it. To investigate the latter, we undertook a case study using the enzyme phosphotriesterase PTE and a series of differentially sized gold NPs AuNPs. PTE, expressed with a terminal hexahistidine sequence, was ratiometrically coordinated to a series of increasing size AuNPs diameter similar or equal to 1.5, 5, 10, 20, 55, 100 nm surface-functionalized with Ni2 -nitrilotriacetic acid ligands and its activity assayed in a comparative format versus that of equivalent amounts of free enzyme controls. PTE-AuNP samples were prepared where the total PTE concentration and NP surface density were kept fixed by varying AuNP concentration along with the converse format. Assembly to the AuNPs increased PTE kcat ca. 3-10-fold depending upon NP size, with the smaller-sized particles showing the highest increase, while enzyme efficiency only increased 2-fold. Further kinetic testing suggested that the PTE enhancement again arose from alleviating its rate limiting step of enzyme-product release and not from a change in the activation energy. Comparison of kcat and enzyme specificity with AuNP diameter revealed that enhancement was directly correlated to AuNP size and curvature with the smaller NPs showing the largest kinetic enhancements.

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Journal Article - Open Access

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Bioconjugate Chemistry , 30, 7, 01 Jan 0001, 01 Jan 0001, [ 1 ] US Naval Res Lab, Ctr Bio Mol Sci and Engn, Code 6900, Washington, DC 20375 USA[ 2 ] US Naval Res Lab, Opt Sci Div, Code 5600, Washington, DC 20375 USA[ 3 ] US Naval Res Lab, Elect Sci and Technol Div, Code 6800, Washington, DC 20375 USA[ 4 ] KeyW Corp, Hanover, MD 21076 USA[ 5 ] CNR, Washington, DC 20001 USA



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