Reasonably, to improve its alkaline pH tolerance, the corresponding regions in Geobacillus sp.TF16 endoxylanase were further engineered by swapping with negatively-charged amino acid-rich regions from B. halodurans C-125 endoxylanase.
Upon contacting with bacteria, the PIC nanosystem disintegrates presumably due to competitive binding of polycation blocks with negatively-charged bacterial surfaces.
In addition, phosphate has been shown to compete with negatively-charged proteins when binding to certain surfaces [32], but conversely, the binding of four proteins to montmorillonite and kaolinite clays increased in phosphate buffer compared to DI water [33].
This causes clustering of positive charges around Lys112 and Lys115, and may result in structural destabilization by electrostatic repulsion and undesired interactions with negatively-charged molecules.
Fluorescent conjugated polythiophene derivative used in this study binds nucleic acids via electrostatic interactions with negatively-charged phosphate groups of the DNA backbone [ 4, 5].
In some cases, small lipophilic targeting molecules that have hepatobiliary excretion can be modified with negatively-charged groups and hydrophilic isotope-binding groups that can greatly reduce hepatobiliary excretion while increasing renal excretion of the non-targeted imaging agent [50 53].
This excess of charged residues may enhance protein stability in thermophilic eukaryotes, notably by increasing salt-bridges, if they can interact with negatively-charged residues.
Indeed, it was recently demonstrated that VSOP can bind strongly to cell membranes via interactions with negatively-charged GAGs (glycosaminoglycans) (Ludwig et al., 2013).
The anticoagulation function of the BTSP family is also supported by the fact that positively-charged proteins can interfere with negatively-charged membranes of activated platelets [ 31].
Histone acetylation restores the positive charge of lysine residues, loosening their interaction with negatively-charged DNA.
