An ATPase in sensitive plant Mimosa pudica. I. Purification and characterization

Bioinspired Self-Resettable Hydrogel Actuators Powered by a Chemical Fuel

The movements of soft living tissues, such as muscle, have sparked a strong interest in the design of hydrogel actuators; however, so far, typical manmade examples still lag behind their biological counterparts, which usually function under nonequilibrium conditions through the consumption of high-energy biomolecules and show highly autonomous behaviors. Here, we report on self-resettable hydrogel actuators that are powered by a chemical fuel and can spontaneously return to their original states over time once the fuels are depleted. Self-resettable actuation originates from a chemical fuel-mediated transient change in the hydrophilicity of the hydrogel networks. The actuation extent and duration can be programmed by the fuel levels, and the self-resettable actuation process is highly recyclable through refueling. Furthermore, various proof-of-concept autonomous soft robots are created, resembling the movements of soft-bodied creatures in nature. This work may serve as a starting point for the development of lifelike soft robots with autonomous behaviors.

Purification and biochemical characterization of a novel ecto-apyrase, MP67, from Mimosa pudica

We have previously reported the presence of an apyrase in Mimosa pudica. However, only limited information is available for this enzyme. Thus, in this study, the apyrase was purified to homogeneity. The purified enzyme had a molecular mass of around 67 kD and was able to hydrolyze both nucleotide triphosphate and nucleotide diphosphate as substrates. The ratio of ATP to ADP hydrolysis velocity of the purified protein was 0.01 in the presence of calcium ion, showing extremely high substrate specificity toward ADP. Thus, we designated this novel apyrase as MP67. A cDNA clone of MP67 was obtained using primers designed from the amino acid sequence of trypsin-digested fragments of the protein. In addition, rapid amplification of cDNA ends-polymerase chain reaction was performed to clone a conventional apyrase (MpAPY2). Comparison of the deduced amino acid sequences showed that MP67 is similar to ecto-apyrases; however, it was distinct from conventional apyrase based on phylogenetic classification. MP67 and MpAPY2 were expressed in Escherichia coli, and the recombinant proteins were purified. The recombinant MP67 showed high substrate specificity toward ADP rather than ATP. A polyclonal antibody raised against the recombinant MP67 was used to examine the tissue distribution and localization of native MP67 in the plant. The results showed that MP67 was ubiquitously distributed in various tissues, most abundantly in leaves, and was localized to plasma membranes. Thus, MP67 is a novel ecto-apyrase with extremely high substrate specificity for ADP.

Mimosa pudica apyrase requires polysaccharide and Ca2+ for the activity

Mimosa pudica Linn leaves with pulvini contain unique isoforms (I and II) of Apyrase enzyme (EC 3.6.1.5). The activity of isoform I depends on divalent cation Mn2+. This isoform is associated noncovalently with the polysaccharide, containing mainly of galactose and arabinose sugars. The apparent molecular mass of these 2 isoforms are 36 and 34 Kd respectively. The association of the polysaccharide with the isoform I has been found to be Ca2+ dependent which is endogenously present in this isoform. Removal of Ca2+ and polysaccharide from the enzyme (isoform I) leads to an inactivation. The enzyme activity can be restored when both Ca2+ and endogenous polysaccharide fraction were added at an optimal molar ratio of Ca2+:protein of 7:1. The endogenous polysaccharide can be replaced by the standard arabinogalactan. No other sugar or polysaccharide except the arabinogalactan can restore the apyrase activity. Calcium mediates a conformational change in the protein which helps in association of polysaccharide as evidenced from fluorometric and far UV-CD studies to restore the enzymic activity. Neither any interaction of the polysaccharide with the protein is detected in absence of Ca2+ nor the enzyme activity could be recovered under such condition.