The Mighty Arginine, the Stable Quaternary Amines, the Powerful Aromatics, and the Aggressive Phosphate:  Their Role in the Noncovalent Minuet

Abstract

In the age of proteomics, the role of certain amino acid residues and some post-translational modifications in noncovalent complex formation are gaining in importance, as the understanding of interactions between biological molecules, is at the heart of the structure function relationship puzzle. In this work, mass spectrometry is used to highlight ammonium- or guanidinium-aromatic interactions through Cation-pi bonds and ammonium- or guanidinium-phosphate interactions through salt bridge formation. Such interactions are crucial factors in certain ligand-receptor interactions and receptor-receptor interactions. In addition, the ability of phosphorylated residues and phosphorylated lipids to form noncovalent complexes with guanidinium and quaternary ammonium (mostly through Coulombic interactions) is demonstrated, and could explain the stability of certain membrane embedded protein, or a possible role for phosphorylation in protein-protein interactions. Dougherty's work demonstrates cation-pi interactions in intra-protein interactions and folding, the present work explores inter-peptide interactions, i.e., the formation of noncovalent complexes between peptides' epitopes containing adjacent aromatic residues and ones containing adjacent Arg as a model to better understand the role of cation-pi complexes in protein-protein interaction. Complexes of peptides containing aromatic residues with quaternary amines as well as the interaction of aromatic compounds, with the guanidinium group of Arg are also investigated. Considering that an inordinate number of therapeutic compounds contain aromatic rings and quaternary amines, the above-described interactions could possibly be of great importance in better understanding their mechanism of action.

Allosteric Modulation of Dopamine D2 Receptors by Homocysteine

“…Mixing homocysteine with different control peptides that did not contain adjacent Arg residues showed no formation of NCXs (data not shown). As previously shown with the Arg-phosphate electrostatic interaction and the Arg-aromatic interaction, 25,26 more than one adjacent Arg's were required for the Arg-thiol electrostatic interaction (data not shown). As previously reported, the D2 receptor epitope 215VLRRRRKRVN224 (10 µM) formed NCXs with the A2A receptor epitope containing pSer374 (266NRRRVEAARR275) (150 µM) (Figure 5a).…”

G protein-coupled receptor-receptor interactions give integrative dynamics to intercellular communication

“…An interesting finding from computational and experimental studies on GPCR oligomerization interfaces is the presence at the interface of specific motifs that appear of particular importance for the allosteric interaction. As demonstrated by Woods and colleagues (Woods, 2004;, the electrostatic interactions between intracellular domains occur between a negatively charged serine-phosphate-containing intracellular motif of one receptor and a positively charged arginine-rich motif of a second receptor. Once established, they possess a covalent-like stability and likely represent the main mechanism for heteromer assemblage.…”

Elucidating the site of protein-ATP binding by top-down mass spectrometry

“…On the other end of the stability scale, the strength of electrostatic interactions is significantly enhanced in the absence of solvent [2,10,[15][16][17][18][19]. The influence of solvent on electrostatic interactions and their role in noncovalent complexes has been described [11,20,21].…”