Does changing the predicted dynamics of a phospholipase C alter activity and membrane binding?

The enzymatic activity of secreted phosphatidylinositol-specific phospholipase C (PI-PLC) enzymes is associated with bacterial virulence. Although the PI-PLC active site has no obvious lid, molecular-dynamics simulations suggest that correlated loop motions may limit access to the active site, and two Pro residues, Pro(245) and Pro(254), are associated with these correlated motions. Whereas the region containing both Pro residues is quite variable among PI-PLCs, it shows high conservation in virulence-associated, secreted PI-PLCs that bind to the surface of cells. These regions of the protein are also associated with phosphatidylcholine binding, which enhances PI-PLC activity. In silico mutagenesis of Pro(245) disrupts correlated motions between the two halves of Bacillus thuringiensis PI-PLC, and Pro(245) variants show significantly reduced enzymatic activity in all assay systems. PC still enhanced activity, but not to the level of wild-type enzyme. Mutagenesis of Pro(254) appears to stiffen the PI-PLC structure, but experimental mutations had minor effects on activity and membrane binding. With the exception of P245Y, reduced activity was not associated with reduced membrane affinity. This combination of simulations and experiments suggests that correlated motions between the two halves of PI-PLC may be more important for enzymatic activity than for vesicle binding.

Some thoughts on the existence of ion and water channels in highly dense and well-ordered CH3-terminated alkanethiol self-assembled monolayers on gold.

Through extensive and systematic reviewing of literatures, this paper presents some thoughts on the existence of ion and water channels in highly dense and well-ordered CH(3)-terminated alkanethiol self-assembled monolayers (C(n)SH-SAMs) on gold: (1) based on the combinational effect of "the van der Waals interaction between the neighbor hydrocarbon chains", "the framework size of C(n)SH molecule" and "the surface lattice structure of C(n)SH-SAMs on gold", a simple ideal model of the close-packed C(n)SH-SAMs is proposed for the first time. The channel with an appropriate diameter of about 3A ( approximately 3A) existing in SAMs on Au is deduced, which is found large enough for ions and water molecules to permeate; (2) through summarizing the literature reports for various experiments (e.g. scan microscopy techniques and electrochemical methods, etc.), the existence of the ion and water channels ( approximately 3A) in close-packed C(n)SH-SAMs is verified; (3) furthermore, the effect of the ions and water molecules permeation on the studies of the SAMs' electron tunneling process is discussed. This simple ideal model of the close-packed C(n)SH-SAMs established by us may clarify the controversies about the permeation mechanism of ions and water molecules in C(n)SH-SAMs.