Magnetically Levitated Plasma Proteins

Surprisingly,
the densities of proteins in solution, which are
important fundamental biophysical quantities, have not been accurately
measured. The lack of such data can limit meaningful interpretation
of physical and chemical features of proteins and enzymes. Here, we
demonstrate a new technique using superparamagnetic iron oxide nanoparticles
(SPIONs) for magnetic levitation (MagLev), which promises to more
precisely measure the density of proteins in solution. As a test of
our new technique, we have levitated human plasma proteins using MagLev.
By using standard density glass beads for calibration, MagLev showed
that the levitated plasma proteins have a measured density in solution
of 1.03 ± 0.02 g/cm3, which is much lower than those
reported or assumed in the past literature (i.e., ∼1.35 g/cm3). Our findings suggest that MagLev may provide useful insights
into the measurement of densities for better understanding the solution
properties of proteins and their interactions both with other proteins
in solution and with solvating water molecules.