Interdomain Linker of the Bioelecrocatalyst Cellobiose Dehydrogenase Governs the Electron Transfer

Direct bioelectrocatalysis applied in biosensors, biofuelcells,and bioelectrosynthesis is based on an efficient electron transferbetween enzymes and electrodes in the absence of redox mediators.Some oxidoreductases are capable of direct electron transfer (DET),while others achieve the enzyme to electrode electron transfer (ET)by employing an electron-transferring domain. Cellobiose dehydrogenase(CDH) is the most-studied multidomain bioelectrocatalyst and featuresa catalytic flavodehydrogenase domain and a mobile, electron-transferringcytochrome domain connected by a flexible linker. The ET to the physiologicalredox partner lytic polysaccharide monooxygenase or, ex vivo, electrodesdepends on the flexibility of the electron transferring domain andits connecting linker, but the regulatory mechanism is little understood.Studying the linker sequences of currently characterized CDH classeswe observed that the inner, mobile linker sequence is flanked by twoouter linker regions that are in close contact with the adjacent domain.A function-based definition of the linker region in CDH is proposedand has been verified by rationally designed variants of Neurospora crassa CDH. The effect of linker lengthand its domain attachment on electron transfer rates has been determinedby biochemical and electrochemical methods, while distances betweenthe domains of CDH variants were computed. This study elucidates theregulatory mechanism of the interdomain linker on electron transferby determining the minimum linker length, observing the effects ofelongated linkers, and testing the covalent stabilization of a linkerpart to the flavodehydrogenase domain. The evolutionary guided, rationaldesign of the interdomain linker provides a strategy to optimize electrontransfer rates in multidomain enzymes and maximize their bioelectrocatalyticperformance.

Automated summary

Direct bioelectrocatalysis involves efficient electron transfer between enzymes and electrodes without the use of redox mediators, and has applications in biosensors, biofuel cells, and bioelectrosynthesis. Cellobiose dehydrogenase (CDH) is a well-studied multidomain bioelectrocatalyst with a catalytic flavodehydrogenase domain and a mobile, electron-transferring cytochrome domain linked by a flexible linker. This study investigates the regulatory mechanism of the linker on electron transfer in CDH and proposes a function-based definition of the linker region. The findings provide insights into optimizing electron transfer rates in multidomain enzymes and enhancing their bioelectrocatalytic performance through rational design of the interdomain linker.