Abstract
While proteins have been treated as particles with a spherically symmetric interaction, of course in reality, the situation is rather more complex. A simple step toward higher complexity is to treat the proteins as non-spherical particles and that is the approach we pursue here. We investigate the phase behavior of the enhanced green fluorescent protein (eGFP) under the addition of a non-adsorbing polymer, polyethylene glycol. From small angle x-ray scattering, we infer that the eGFP undergoes dimerization and we treat the dimers as spherocylinders with aspect ratio L/D - 1 = 1.05. Despite the complex nature of the proteins, we find that the phase behavior is similar to that of hard spherocylinders with an ideal polymer depletant, exhibiting aggregation and, in a small region of the phase diagram, crystallization. By comparing our measurements of the onset of aggregation with predictions for hard colloids and ideal polymers [S. V. Savenko and M. Dijkstra, J. Chem. Phys. 124, 234902 (2006) and Lo Verso et al., Phys. Rev. E 73, 061407 (2006)], we find good agreement, which suggests that the behavior of the eGFP is consistent with that of hard spherocylinders and ideal polymers.
Highlights
Protein aggregation and crystallization have important consequences in determining their structure and function and understanding challenges ranging from condensation diseases1–3 to the development of new materials.4 Controlling their assembly into states in which their functionality can be exploited is crucial to fully realize their potential, and crystallization is fundamental to obtaining protein structure and insights into their function
Despite the complex nature of the proteins, we find that the phase behavior is similar to that of hard spherocylinders with an ideal polymer depletant, exhibiting aggregation and, in a small region of the phase diagram, crystallization
We studied the phase behavior of a model system of fluorescent proteins and polymers in the “colloid limit” where the polymer depletant is smaller than or comparable in size to the protein
Summary
Protein aggregation and crystallization have important consequences in determining their structure and function and understanding challenges ranging from condensation diseases to the development of new materials. Controlling their assembly into states in which their functionality can be exploited is crucial to fully realize their potential, and crystallization is fundamental to obtaining protein structure and insights into their function. Protein aggregation and crystallization have important consequences in determining their structure and function and understanding challenges ranging from condensation diseases to the development of new materials.. Protein aggregation and crystallization have important consequences in determining their structure and function and understanding challenges ranging from condensation diseases to the development of new materials.4 Controlling their assembly into states in which their functionality can be exploited is crucial to fully realize their potential, and crystallization is fundamental to obtaining protein structure and insights into their function. In average, only 0.04% of crystallization experiments yield good quality crystals.. In average, only 0.04% of crystallization experiments yield good quality crystals.8 This is due, in part, to the inherent protein shape and surface complexity as well as the dependence of protein–protein interactions on combinations of pH, temperature, and precipitants (salts and polymers). In average, only 0.04% of crystallization experiments yield good quality crystals. This is due, in part, to the inherent protein shape and surface complexity as well as the dependence of protein–protein interactions on combinations of pH, temperature, and precipitants (salts and polymers).
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