11,795 research outputs found
Capillarity-like growth of protein folding nuclei
We analyzed folding routes predicted by a variational model in terms of a
generalized formalism of the capillarity scaling theory for 28 two-state
proteins. The scaling exponent ranged from 0.2 to 0.45 with an average of 0.33.
This average value corresponds to packing of rigid objects.That is, on average
the folded core of the nucleus is found to be relatively diffuse. We also
studied the growth of the folding nucleus and interface along the folding route
in terms of the density or packing fraction. The evolution of the folded core
and interface regions can be classified into three patterns of growth depending
on how the growth of the folded core is balanced by changes in density of the
interface. Finally, we quantified the diffuse versus polarized structure of the
critical nucleus through direct calculation of the packing fraction of the
folded core and interface regions. Our results support the general picture of
describing protein folding as the capillarity-like growth of folding nuclei.Comment: 16 pages,6 figures. Submitted to Proc.Natl.Acad.Sc
Loop-closure principles in protein folding
Simple theoretical concepts and models have been helpful to understand the
folding rates and routes of single-domain proteins. As reviewed in this
article, a physical principle that appears to underly these models is loop
closure.Comment: 27 pages, 5 figures; to appear in Archives of Biochemistry and
Biophysic
More is different: 50 years of nuclear BCS
Many of the concepts which are at the basis of the development associated
with a quantitative treatment of the variety of phenomena associated with the
spontaneous breaking of gauge symmetry in nuclei have been instrumental in
connection with novel studies of soft matter, namely of protein evolution and
protein folding. Although the route to these subjects and associated
development does not necessarily imply the nuclear physics connection, such a
connection has proven qualitatively and quantitatively inspiring. In particular
to model protein evolution in terms of the alignment of quasispins displaying
twenty different projections, one for each of the twenty amino acids occurring
in nature, and the associated symmetry breaking in information (sequence)
space. Emergent properties of the corresponding phase transition are domain
walls which stabilize local elementary structures (LES), few groups of 10-20
aminoacids which become structured already in the denatured state provide the
molecular recognition directing protein folding. In fact, their docking is
closely related to the transition state of the process. While the two-step, yes
or no, folding process, does not provide direct information concerning LES, one
can force LES from virtual to become real, observable final state entities.
Getting again inspiration from the nuclear case (virtual processes contributing
to pair correlations can be forced to become real with the help of a probe
which itself changes particle number by two), one would expect that to make
real virtual LES, that is segments of the protein which already at an early
stage of the folding process flicker in and out of their native conformation,
one needs a probe which itself displays a similar behaviour. Peptides
displaying a sequence identical to LES are such probes.Comment: Contribution to the Volume 50 years of Nuclear BCS edited by World
Scientifi
Nucleation phenomena in protein folding: The modulating role of protein sequence
For the vast majority of naturally occurring, small, single domain proteins
folding is often described as a two-state process that lacks detectable
intermediates. This observation has often been rationalized on the basis of a
nucleation mechanism for protein folding whose basic premise is the idea that
after completion of a specific set of contacts forming the so-called folding
nucleus the native state is achieved promptly. Here we propose a methodology to
identify folding nuclei in small lattice polymers and apply it to the study of
protein molecules with chain length N=48. To investigate the extent to which
protein topology is a robust determinant of the nucleation mechanism we compare
the nucleation scenario of a native-centric model with that of a sequence
specific model sharing the same native fold. To evaluate the impact of the
sequence's finner details in the nucleation mechanism we consider the folding
of two non- homologous sequences. We conclude that in a sequence-specific model
the folding nucleus is, to some extent, formed by the most stable contacts in
the protein and that the less stable linkages in the folding nucleus are solely
determined by the fold's topology. We have also found that independently of
protein sequence the folding nucleus performs the same `topological' function.
This unifying feature of the nucleation mechanism results from the residues
forming the folding nucleus being distributed along the protein chain in a
similar and well-defined manner that is determined by the fold's topological
features.Comment: 10 Figures. J. Physics: Condensed Matter (to appear
- …