本組將和Tamas組一起，在生物分子界面自組裝結構和功能領域合作，發表有影響力的工作。
Theoretical and experimental studies of self-assembling protein and lipid systems
Tamás Beke-Somfai
Research Centre for Natural Sciences, Hungarian Academy of Sciences
1117
Budapest, Magyar tudósok krt.2
Summary
In a wide range of biological activities, from cell locomotion to membrane transport, Nature
deploys numerous sophisticated molecular machines which have become highly
optimized for performance and controllability. These assemblies are often
composed of multiple separate components which gather for various specific
purposes. Rational design and engineering of similarly complex biosystems is a
very exciting field with a potential to dramatically alter future’s medicine or
industrial biochemistry [1, 2]. However, to overcome major challenges in areas
such as design of artificial enzymes, or membrane active designed compounds
mimicking natural ones, the precise understanding of their mechanisms especially
of their key steps is required. Here I will focus on two examples where it is
challenging to gain insight to such mechanistic details.
1. FoF1 ATP synthase is interesting as a model
system: a delicate molecular machine synthesizing or hydrolyzing ATP utilizing
a rotary motor. Isolated F1 performs hydrolysis with a rate very
sensitive to ATP concentration. Experimental and theoretical results show that
at low ATP concentrations ATP is slowly hydrolyzed in the so called tight
binding site, whereas at higher concentrations the binding of further ATP
molecules induce rotation of the central g-subunit thereby
forcing the site to transform via subtle conformational changes into a loose
binding site, in which hydrolysis occurs faster. By a combination of
theoretical approaches we addressed how large macromolecular rearrangements may
manipulate 1?-scale rearrangements in the active site and how the reaction rate
changes as a consequence [3]. Simulations reveal that in response to g-subunit position,
the active site conformation is fine-tuned mainly by small a-subunit changes
[4]. It is hoped that in the future the design of bioinspired complex systems
arrives to the age where fine-tuning and precise control on desired processes
can be achieved
2. In the recent decades, development of resistance by bacteria to
antibiotics makes better understanding of antimicrobial mechanisms increasingly
important. Toxic oligomers of antimicrobial peptides (AMPs) may assemble into
hydrophilic or lipophilic complexes and exert their toxicity in a higher level
aggregate form. However, this mechanism is not understood, greatly hindering
rational development of similar compounds.
In this part of the presentation an overview is given on our recent
studies related to both natural and non-natural peptide oligomer assemblies and
their aggregates when associated with organic small molecules. We have
experienced several interactions resulting in induced conformational changes
for these compounds. Several of the observed secondary structures are rather
different from those regularly obtained for well studied AMPs indicating that
the action mechanism of these compounds may be different when exerting their
toxicity in in vivo conditions in presence of a complex multicomponent
environment. Also, I aim to describe new methods available in our laboratory
which are capable to address membrane systems in solution phase. In particular
I will focus on polarized light spectroscopy and on Linear Dichroism coupled to
a Couette Flow-cell (Flow-LD). By today, flow-LD can be used to characterize bicellar
systems or induce lipid bilayer fusion to test mechanisms related to cell
fusion or lipid bilayer mixing [5-7]
[1] Senes Curr. Op. Struct. Biol. 2011, 21, 460-466
[2] Jiang et al. Science, 2008, 319, 1387-1391
[3] Beke-Somfai, et al. Proc. Natl. Acad. Sci. USA, 2011, 108, 4828-4833
[4] Beke-Somfai, et al. Proc. Natl. Acad. Sci. USA, 2013, 6, 2117-2122
[5] Nordén et al. (2010), Linear Dichroism and Circular Dichroism. A Textbook on Polarized-Light Spectroscopy.
[6] Kogan et al. Langmuir, 2014, 30, 4875-4878
[7] Rocha et al. Langmuir, 2016, 32, 2841-2846