Photocatalytic Hydrogen Evolution by a De Novo Designed Metalloprotein that Undergoes Ni‐Mediated Oligomerization Shift
Pallavi Prasad, Leigh Anna Hunt, Ashley E. Pall, Maduni Ranasinghe, Ashley E. Williams, Timothy L. Stemmler, Borries Demeler, Nathan I. Hammer, Saumen Chakraborty
Abstract
Abstract De novo metalloprotein design involves the construction of proteins guided by specific repeat patterns of polar and apolar residues, which, upon self‐assembly, provide a suitable environment to bind metals and produce artificial metalloenzymes. While a wide range of functionalities have been realized in de novo designed metalloproteins, the functional repertoire of such constructs towards alternative energy‐relevant catalysis is currently limited. Here we show the application of de novo approach to design a functional H 2 evolving protein. The design involved the assembly of an amphiphilic peptide featuring cysteines at tandem a/d sites of each helix. Intriguingly, upon Ni II addition, the oligomers shift from a major trimeric assembly to a mix of dimers and trimers. The metalloprotein produced H 2 photocatalytically with a bell‐shape pH dependence, having a maximum activity at pH 5.5. Transient absorption spectroscopy is used to determine the timescales of electron transfer as a function of pH. Selective outer sphere mutations are made to probe how the local environment tunes activity. A preferential enhancement of activity is observed via steric modulation above the Ni II site, towards the N‐termini, compared to below the Ni II site towards the C‐termini.