  We have studied the structure of salt-free lysozyme at 293 K and pH 7.8 using
molecular simulations and experimental SAXS effective potentials between
proteins at three volume fractions, 0.012, 0.033, and 0.12. We found that the
structure of lysozyme near physiological conditions strongly depends on the
volume fraction of proteins. The studied lysozyme solutions are dominated by
monomers only for <0.012; for the strong dilution 70% of proteins are in a form
of monomers. For 0.033 only 20% of proteins do not belong to a cluster. The
clusters are mainly elongated. For 0.12 almost no individual particles exits,
and branched, irregular clusters of large extent appear. Our simulation study
provides new insight into the formation of equilibrium clusters in charged
protein solutions near physiological conditions.
