Proteins are Solitary! Pathways of Protein Folding and Aggregation in Protein Mixtures.

Valentino Bianco,Ivan Coluzza,Desire Di Silvio,Miren Alonso-Navarro,Aitziber L Cortajarena,Sergio Moya

doi:10.1021/acs.jpclett.9b01753

Abstract

We present a computational and experimental study on the folding and aggregation in solutions of multiple protein mixtures at different concentrations. We show how in protein mixtures each component is capable of maintaining its folded state at densities greater than the one at which they would precipitate in single-species solutions. We demonstrate the generality of our observation over many different proteins using computer simulations capable of fully characterizing the cross-aggregation phase diagram of all the mixtures. Dynamic light scattering experiments were performed to evaluate the aggregation of two proteins, bovine serum albumin (BSA) and consensus tetratricopeptide repeat (CTPR), in solutions of one or both proteins. The experiments confirm our hypothesis and the simulations. These findings elucidate critical aspects of the cross-regulation of expression and aggregation of proteins exerted by the cell and on the evolutionary selection of folding and non-aggregating protein sequences, paving the way for new experimental tests.

Highlights

1 After the synthesis at the ribosome, polypeptide chain are exposed to a highly crowded cellular environment, 2 where, despite many non-specific interactions, 3–5 the chain is capable to select for a subset of amino acid contacts which funnel the free energy landscape toward a unique native/folded state. 6–10 cells evolved complex post-translational processes that include chaperones to facilitate proteins to fold
Protein aggregation is mostly unavoidable when proteins are over-expressed at concentrations higher than the physiological one. 11–13 The linear anti-correlation between expression levels and aggregation propensity is a remarkable experimental fact Fig. 1 121, especially considering the large number of protein species present in cells. 14,15
Provided that the expression levels are kept below the precipitation concentration of the isolated species, the result suggests the intriguing possibility that protein folding is unperturbed by the presence of the other proteins

Summary

Introduction

Proteins are involved in a wide range of physiological processes crucial for all living organism. 1 After the synthesis at the ribosome, polypeptide chain are exposed to a highly crowded cellular environment, 2 where, despite many non-specific interactions, 3–5 the chain is capable to select for a subset of amino acid contacts which funnel the free energy landscape toward a unique native/folded state. 6–10 cells evolved complex post-translational processes that include chaperones to facilitate proteins to fold.protein aggregation is mostly unavoidable when proteins are over-expressed at concentrations higher than the physiological one. 11–13 The linear anti-correlation between expression levels and aggregation propensity is a remarkable experimental fact Fig. 1 121 , especially considering the large number of protein species present in cells. 14,15Provided that the expression levels are kept below the precipitation concentration of the isolated species, the result suggests the intriguing possibility that protein folding is unperturbed by the presence of the other proteins. 11–13 The linear anti-correlation between expression levels and aggregation propensity is a remarkable experimental fact Fig. 1 121 , especially considering the large number of protein species present in cells. We present a computational and experimental study to support a different hypothesis to explain the uncorrelated behaviour of protein folding.

Results

Conclusion