J. Biol. Chem., Vol. 262, Issue 31, 14899-14904, Nov, 1987
Interaction of epidermal growth factor with micelles monitored by photochemically induced dynamic nuclear polarization-1H NMR spectroscopy
KH Mayo, A De Marco, E Menegatti and R Kaptein
Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122.
Photochemically induced dynamic nuclear polarization (CIDNP)-1H-NMR
spectroscopy has been used to study the interaction of the protein hormone
epidermal growth factor (EGF) with micelles of sodium dodecyl sulfate (SDS)
and dodecylphosphorylcholine (DPC). Conventional 1H-NMR spectra show that
most protein resonances remain unperturbed when micelles are added to
solution, which argues that the overall protein conformation is maintained
in the presence of SDS or DPC at the concentrations used. Photo-CIDNP
enhancements of resonances assigned to aromatic side chains of residues at
the COOH terminus and beta-sheet regions of murine EGF (i.e. Trp-49,
Trp-50, and Tyr-37) are considerably reduced in the presence of micelles,
while resonances of aromatic side chains of residues found elsewhere on the
protein surface are mostly unaffected. This suggests that the primary
interaction between murine EGF and the micelle occurs at the micelle-bulk
solvent interface. The overall negatively charged surface of SDS micelles
tends to induce a stronger interaction with the protein compared to the
zwitterionic DPC micelles, probably due to electrostatic interactions.
Cleavage of the COOH-terminal pentapeptide containing both tryptophan
residues enhances the already present, but weak, interaction with Tyr- 10
and attenuates it with Tyr-37. A similar interaction pattern is found with
rat EGF suggesting that at least concerning these two species of EGF the
interaction is somewhat specific and conserved. A simple mass-action model
for protein-micelle interaction is also presented.
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