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WHY DO PROTEINS, AND OTHER SYSTEMS CRYSTALLIZE SOMETIMES-AND
NOT OTHERS
K. A. Dawson
New proteins are easy to make nowadays,including those
that are not naturally occurring. However, many attempts to create new proteins
lead to failure because they are not crystallizable, and therefore not characterizable.
There may be a number of reasons.
Amongst these is misfolding, aggregation, and gellation.
Prominent amongst these is the fact that, even if well-folded, proteins
are very hard to crystallize.
We study two simple models of colloidal systems, proteins,
and other meso-nanoscopic objects to develop an understanding of the factors
leading to good crystals, rather than amorphous matter. In both cases, the
attractions between particles are considered to be attractive and short ranged,
in line with modern opinion on that topic.
We argue that the main features of this type of problem are
similar to other issues such as protein folding, that have multiple minima
and produce 'glassy' phenomena. Here, however, the lack of moleular connectivity
in the problem simplifies it somewhat, and leads us to be able to make progress
in theory and simulation.
When the multiple minimum aspect of the system predominates,
we find glasses, gels, and similar materials. The main challenge is to understand
the control parameters of the system, and thereby make it possible to form
good (say protein) crystals, rather than disordered materials.
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