Aggregation properties of a disordered protein are tunable by pH and depend on its net charge per residue

• Published in: Biochimica et biophysica acta. General subjects Vol. 1861; no. 11; pp. 2543 - 2550
• Main Authors: Tedeschi, Giulia, Mangiagalli, Marco, Chmielewska, Sara, Lotti, Marina, Natalello, Antonino, Brocca, Stefania
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.11.2017
• Subjects: amino acid composition; Amino Acid Sequence - genetics; electrostatic interactions; green fluorescent protein; Hydrogen-Ion Concentration; Hydrophobic and Hydrophilic Interactions; hydrophobicity; IDPs; Intrinsically Disordered Proteins - chemistry; Intrinsically Disordered Proteins - genetics; Isoelectric point; Kinetics; Measles morbillivirus; Measles virus - chemistry; Measles virus - genetics; moieties; NCPR; phosphoproteins; Protein Aggregates - genetics; Protein aggregation; Protein Conformation; Protein Folding; Protein solubility; Solubility; Static Electricity; Viral Proteins - chemistry; Viral Proteins - genetics; CD; Protein aggregation; IMAC; Protein solubility; GFP; RC; PB; NCPR; FCR; Isoelectric point; FTIR; PNT; pI; IDPs; ATR
• ISSN: 0304-4165; 1872-8006
• DOI: 10.1016/j.bbagen.2017.09.002

Intrinsically disordered proteins (IDPs) possess a peculiar amino acid composition that makes them very soluble. Nevertheless, they can encounter aggregation in physiological and pathological contexts. In this work, we addressed the issue of how electrostatic charges can influence aggregation propensity by using the N-terminus moiety of the measles virus phosphoprotein, PNT, as a model IDP. Taking advantage of the high sequence designability of IDPs, we have produced an array of PNT variants sharing the same hydrophobicity, but differing in net charges per residue and isoelectric points (pI). The solubility and conformational properties of these proteins were analysed through biochemical and biophysical techniques in a wide range of pH values and compared with those of the green fluorescence protein (GFP), a globular protein with lower net charge per residue, but similar hydrophobicity. Tested proteins showed a solubility minimum close to their pI, as expected, but the pH-dependent decrease of solubility was not uniform and driven by the net charge per residue of each variant. A parallel behaviour was observed also in fusion proteins between PNT variants and GFP, which minimally contributes to the solubility of chimeras. Our data suggest that the overall solubility of a protein can be dictated by protein regions endowed with higher net charge per residue and, hence, prompter to respond to pH changes. This finding could be exploited for biotechnical purposes, such as the design of solubility/aggregation tags, and in studies aimed to clarify the pathological and physiological behaviour of IDPs. [Display omitted] •Intrinsically disordered proteins lose solubility at isoelectric point (pI).•The extent of solubility loss depends on net charge per residue (NCPR).•Chimeric proteins with high- and low-NCPR moieties lose solubility at their average pI.•In chimeric proteins, high-NCPR moiety drives the loss of solubility.