Evolutionarily elderly proteins commonly feature greater catalytic promiscuity. Cytochrome c is among the first set of proteins in evolution to have known prospects in electron transport and peroxidative properties. Here, we report that cyt c is also a proficient proton‐transfer catalyst and enhances the Kemp elimination (KE; model reaction to show proton transfer catalytic property) by ∼750‐fold on self‐organized systems like micelles and vesicles. The self‐organized systems mimic the mitochondrial environment in vitro for cyt c. Using an array of biophysical and biochemical mutational assays, both acid–base and redox mechanistic pathways have been explored. The histidine moiety close to hemin group (His18) is mainly responsible for proton abstraction to promote the concerted E2 pathway for KE catalysis when cyt c is in its oxidized form; this has also been confirmed by a H18A mutant of cyt c. However, the redox pathway is predominant under reducing conditions in the presence of dithiothreitol over the pH range 6–7.4. Interestingly, we found almost 750‐fold enhanced KE catalysis by cyt c compared to aqueous buffer. Overall, in addition to providing mechanistic insights, the data reveal an unprecedented catalytic property of cyt c that could be of high importance in an evolutionary perspective considering its role in delineating the phylogenic tree and also towards generating programmable designer biocatalysts.

Tip-links as gating-spring in the mechanotransduction in hearing is still a debate. While the molecular elasticity of individual tip-link proteins warrants its candidature, the apparent rigidity from the heterotetrameric tip-links assembly refutes the claim. Using force-clamp experiments and simulations, we report that the heterotetrameric assembly is the natural selection for the gating-springs. Tip-links follow slip-ideal-slip bonds with increasing force. While in slip, the complex dissociates monotonously, ideal-bond interface responds indifferently to various auditory inputs. Insensitivity to forces renders tip-links as low-force pass filter, characteristic of gating-spring. Individual tip-links, however, forms slip-catch-slip bonds under tension. While catch bonds turn stronger with force from loud sound, our Langevin dynamics indicated the transition from slip-catch to slip-ideal bonds as cooperative effect of the dimers of individual protein complexes in tip-links. From molecular dynamics, we deciphered the molecular mechanism of catch bonds and its importance in deafness.

The evolutionary drive towards specificity has developed individual enzymes for specific reactions; however, some ancient proteins/enzymes display promiscuous substrate specificity, which is central theme of the image. We have shown that cytochrome c, one of the oldest members of the protein family, known for electron transport and peroxidative properties in lipid membranes, is also capable of performing proton transfer, but only in membrane‐mimetic media. We discovered that His18, close to the hemin group, is mainly responsible for proton abstraction. This result is not only important in evolutionary perspectives, but also exemplifies the differential behavior of biomolecules in response to their surroundings. More information can be found in the full paper by S. Maiti et al.

β-strands in proteins undergo anti-cross correlated crankshaft-type motions and adapt to the input mechanical cues. However, a direct study to reveal the molecular relation of force-adaptability with crankshaft motions of β-strands is long-awaited. To elucidate, here we explore the differences in mechanical tolerance of a gating-spring protein in hearing, cadherin-23, with genotypic and phenotypic variations on a single residue. Though the variants possess comparable topology, differ in contact-orders. Higher contact-order induces higher crankshaft. We identified that the variants with higher crankshaft exhibit larger heterogeneity in the conformational state space and thus, higher force-tolerance. However, protein-variants with lower contact-orders possess higher folding-cooperativity and faster intrinsic-folding, though their folding-energy landscape is most prone to distortion under tension. Overall, our study provides a unique relation between the transition-cooperativity amongst the sparsely populated conformational states and the force-adaptations by β-rich proteins. The use of phenotype and genotype variants also help us to deduce the mechanical fingerprinting of healthy spring and malicious spring.