Molecular scales on biological membranes

Date:
October 12, 2021
Source:
Max-Planck-Gesellschaft
Summary:
With mass-sensitive particle tracking scientists can determine
location and size changes of unlabeled proteins on membranes


FULL STORY ==========================================================================
A large proportion of biologically relevant processes take place at
membranes.

Studying the dynamics of these processes in real time and without
disturbing the biological system is still a major methodological
challenge. A team led by Petra Schwille, director at the Max
Planck Institute of Biochemistry, and Nikolas Hundt from the Ludwig-Maximilians-Universita"t Mu"nchen has now developed a new method
for this purpose: Mass-Sensitive Particle Tracking (MSPT). Using MSPT,
the movements and reactions of individual unlabeled proteins on biological membranes can be determined solely by their mass.


========================================================================== Cellular processes on membranes are often fast and short-lived. Molecules assemble briefly, separate again, interact with different partners and
move along or through the membrane. It is therefore important to not
only study static snapshots of these processes, but also to understand
their dynamics. But how can this be achieved methodically? Petra Schwille
from the Max Planck Institute of Biochemistry and Nikolas Hundt from the
Ludwig Maximilians University together with their team have developed
the method Mass-Sensitive Particle Tracking -- MSPT, which allows to
analyze proteins during dynamic processes on membranes.

The starting point for the biophysicists were recent advancements
in mass photometry, which could already be used to determine the
molecular mass of unlabeled molecules in solution. What is new about
MSPT is that the dynamics of membrane-associated proteins can now be
tracked in their biologically plausible environment. In this process, individual proteins are identified by their molecular mass without
the need for labeling. Frederik Steiert, one of the first authors
of the publication, says: "We can now track directly on biological
membranes what mass individual proteins have, how they move and how they interact. This allows us to study the dynamics of biological systems in
greater detail." Analyzing dynamic processes is particularly important
in biology as many processes at the membrane are transient.

Mass determination by light scattering What principles is the
new method based on? When light hits a particle, the light is
scattered. The intensity of the scattered light depends on the mass of
the particle. Videos in which individual proteins on membranes are made directly visible are recorded with a microscope. With the aid of analysis software, these proteins can be tracked and their scattering signal,
and thus their mass, can be determined. This is currently possible for
proteins with a molecular weight of at least 50 kDa, i.e. for a large
part of all known proteins. Another advantage of the new MSPT method is
that proteins do not have to be labeled. Labeling can be achieved, for
example, by attaching fluorescent tags to molecules. However, labeling
poses the risk that proteins could be impaired in their function or
that the fluorescent labels could bleach during the experiment. By using
MSPT, in contrast, methodological problems that can arise from labeling
are prevented.

MinDE protein system To demonstrate the potential of the method for
biological questions, the biophysicists used an established system from
the Schwille laboratory: the MinDE protein system from the bacterium Escherichia coli (E. coli). MinD and MinE proteins are involved in E. coli
cell division. Tamara Heermann, another first author, says: "The method
permits us to characterize properties of dynamical systems that were
previously not measurable. This allowed us not only to verify established findings about the Min system, but also to gain new insights." By using
MSPT, the team was able to show that the complexes of MinD proteins are
larger than initially thought. In addition, the experiments provide first insights that MinE can act as a connecting piece for MinD proteins and
that it can thus initiate the membrane release of larger complexes.

As reported in the new paper, MSPT provides valuable insights for
elucidating dynamic processes at biological membranes. However, the
researchers are continuously working on improving the method even
further. In the future, the method should also be applicable for
integral membrane proteins and it should allow the detection of even
smaller proteins.

========================================================================== Story Source: Materials provided by Max-Planck-Gesellschaft. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Tamara Heermann, Frederik Steiert, Beatrice Ramm, Nikolas Hundt,
Petra
Schwille. Mass-sensitive particle tracking to elucidate the
membrane- associated MinDE reaction cycle. Nature Methods, 2021;
18 (10): 1239 DOI: 10.1038/s41592-021-01260-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211012130547.htm

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