Disordered Motifs and Domains in Cell Control
Monday Speaker Abstracts
Intrinsically Disordered Titin PEVK Motifs: The Interplay of Force, Form, and Function
of an Ion-exchange Driven Elastomer
Kuan Wang
1,3
, Richard J. Wittebort
2
, Leffrey G. Forbes
3
, Wanxia L. Tsai
3
, S Arumugam
2
.
1
Academia Sinica, Nankang, Taipei, Taiwan,
2
University of Louisville, Louisville, KY,
USA,
3
NIAMS, NIH, Bethesda, MD, USA.
We describe the interplay between elasticity and ensemble structures of intrinsically disordered
proteins, using the PEVK segment of the giant (~3-4 MDa) elastic protein titin as a model. Titin
PEVK is an highly extended scaffold protein segment encoded by splicing of more than 100
exons and is thought to integrate mechanical stress and SH3-mediated signaling pathways (J.
Biol. Chem,281, 27539-556, 2006).
Solution and gel phase NMR, single molecule force spectroscopy and steered molecular
dynamics simulations were used to investigate the ensemble structures and ion-pair interactions
of an engineered 15-mer polyprotein, consisting of 15 identical titin PEVK modules, with
affinity tags at both ends to facilitate nanomechanical measurements by single molecule atomic
force microscopy.
Using the NMR data for the polypeptide backbone and a subset of possible long range
interactions, we were able to simulate an ensemble of representative structures and to simulate
the mechanical stretching of a trimer and compare it to the stretching of the single polyprotein by
atomic force microscopy. The stretching simulations showed that the attractive ionic interactions
are in constant flux, leading to an elastic behavior similar to entropic polymers. Some of the
simulations showed the exact force signature as those seen in experimental force spectra, and the
force-bearing events arise from either transient hydrophobic residues, depending upon the
trajectory of the stretching polymer.
The current work tightly integrates both experiments and simulations to provide a more complete
understanding of how intrinsically disordered ampholytes behaves as an elastic element by an
intrachain ion-exchange mechanism. Our insights of nanomechanical properties of this
intrinsically disordered protein are useful in the understanding of how force modulates function
and in the design of elastic functional elastic biomaterials.
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