Higher plants reorient their growth direction by sensing the organ tilt relative to the direction of gravity (gravitropism). Historically famous “the starch statolith hypothesis” has explained how plants sense their organ tilt, that is, starch accumulating amyloplasts with high density sink like stones along the gravity vector in the cell, and then trigger subsequent signalings. Recent molecular genetic studies suggest that the sedimentation of amyloplasts is not a spontaneous event but is controlled by actin filaments and vacuolar membranes. This review mainly focuses on the mechanisms of gravity perception involving the amyloplasts movement and following signaling events during gravitropism.
Cinnamycin (Ro09-0198) and duramycin are toxins of 19 amino acid cyclic peptides derived from Streptomyces species that specifically bind ethanolamine phospholipids such as phosphatidylethanolamine (PE) and phosphatidylethanolamine plasmalogen. Since PE preferentially distributes in the cytoplasmic leaflet of the plasma membrane, the strategy of the toxin seems inefficient. However, the toxins use tricks to exhibit the toxicity.
On the ideology of minimalism, we have designed a micro-protein consisting of only 10 amino acids. The molecule, CLN025, exhibits a β-hairpin structure in both crystalline state and aqueous solution. Thermal unfolding is shown to be reversible and can be fitted as a two-state transition. Molecular dynamics simulation starting from an extended conformation leads to a funnel-shaped surface and scale-free network, being the structures located at the bottom and the hub similar to the experimental ones. Considering these consequences, we proposed the concept of “ideal protein” as a way to clarify the differences between “protein” and “peptide”.