ac5b01725_si_001.pdf (3.54 MB)
Membrane-Associated Conformation of HIV‑1 Nef Investigated with Hydrogen Exchange Mass Spectrometry at a Langmuir Monolayer
journal contribution
posted on 2015-07-21, 00:00 authored by Gregory
F. Pirrone, Lori A. Emert-Sedlak, Thomas E. Wales, Thomas E. Smithgall, Michael S. Kent, John R. EngenIn
the companion paper to this work, we described development of
a new type of hydrogen exchange (HX) mass spectrometry (MS) measurement
that integrates Langmuir monolayers. With Langmuir monolayers, the
lipid packing density can be reproducibly controlled and changed as
desired. Analysis of HX in proteins that may undergo conformational
changes as a function of lipid packing (for example, conformational
rearrangements after insertion into a lipid layer) are then possible.
We previously used neutron reflection to characterize just such a
conformational change in the myristoylated HIV-1 Nef protein (myrNef):
at high lipid packing density, myrNef could not insert into the lipids
and maintained a compact conformation adjacent to the monolayer, whereas
at lower lipid packing density, myrNef was able to insert N-terminal
arm residues, causing displacement of the core domain away from the
monolayer. In order to locate where conformation may have been altered
by lipid association, we applied the HX MS Langmuir monolayer method
to myrNef associated with monolayers of packing densities identical
to those used for the prior neutron reflection measurements. The results
show that the N-terminal region and the C-terminal unstructured loop
undergo conformational changes when associated with a low density
lipid monolayer. The results are not consistent with the hypothesis
of myrNef dimerization upon membrane association in the absence of
other myrNef binding partners. The HX MS Langmuir monolayer method
provides new and meaningful information for myrNef that helps explain
necessary conformational changes required for function at the membrane.