Experimental evidence shows that the mechanism of pore formation by actinoporins is a multistep process, involving binding of the water-soluble monomer to the membrane and subsequent oligomerization on the membrane surface, leading to the formation of a functional pore.
BCM association prevents ATP turnover by an unexpected mechanism, occluding the binding of the nucleophilic water molecule required for ATP hydrolysis.
The structure is suggestive of the repositioning, during substrate binding, of the catalytic water for activation and subsequent nucleophilic attack.
The Thr to Leu substitutions disrupt the binding of the ordered water to sbwAFP by removing the stabilizing hydroxyl side chain hydrogen bond interactions of the threonine residues.
These events represent important pieces of a clear-cut mechanistic rationale behind the failure of the NMO-IgG binding, while the water channel function as well as the propensity to aggregate into OAPs remains unaltered.
The water exchange study showed that the mutant weakens the binding of substrate water to the OEC.
However, in contrast with the SmARG ABH complex, the additional α-substituents of ABHPE and ABHDP block the binding of water molecule W4; this water molecule ordinarily mediates a hydrogen bond between the inhibitor α-amino group and D213.
Likewise, the increase in frictional ratio observed in the experiment compared to the Zeno simulation for the anhydrous particle is likely caused by the binding of water molecules at the ends of the benzoate residues, replacing the overall globular shape of the anhydrous particle with more extended spike-like shapes.
In contrast, the binding of water to the Fe center causes only a modest perturbation to the original Fe ligand bonds, as expected considering that water is a weak field ligand.
The proposed binding surfaces of many ferredoxins are covered with water, so the binding of the partners will release water molecules and favor the reaction entropically.
14 In addition to the aforementioned, the higher relative HA concentration of JUP (24 mg/mL vs 20 mg/mL) might convey a greater lifting ability through the binding of more water molecules, in comparison with the PER gel, which may also contribute to the relative longevity of JUP as observed in the current study.
