Structural adaption in living systems is achieved by competing catalytic pathwayst hat drive assembly and disassembly of molecular components under the influence of chemical fuels.W er eport on as imple mimic of such as ystem that displays transient, sequence-dependent formation of supramolecular nanostructures based on biocatalytic formation and hydrolysis of self-assembling tripeptides.The systems are catalyzedb ya-chymotrypsin and driven by hydrolysis of dipeptide aspartyl-phenylalanine-methyl ester (the sweetener aspartame,D F-OMe). We observed switch-like pathway selection, with the kinetics and consequent lifetime of transient nanostructures controlled by the peptide sequence.I nd irect competition, kinetic (rather than thermodynamic) component selection is observed.

The reversible regulation of catalytic activity is af eature found in natural enzymes whichi sn ot commonly observed in artificial catalytic systems.H ere,w ef abricate an artificial hydrolase with pH-switchable activity,a chieved by introducing ac atalytic histidine residue at the terminus of apH-responsive peptide.The peptide exhibits aconformational transition from random coil to b-sheet by changing the pH from acidic to alkaline.The b-sheet self-assembles to form long fibrils with the hydrophobic edge and histidine residues extending in an ordered arraya st he catalytic microenvironment, which shows significant esterase activity.C atalytic activity can be reversible switched by pH-induced assembly/ disassembly of the fibrils into random coils.A th igher concentrations,t he peptide forms ah ydrogel whichi sa lso catalytically active and maintains its reversible (de-)activation.