  Crystallography may be the gold standard of protein structure determination,
but obtaining the necessary high-quality crystals is also in some ways akin to
prospecting for the precious metal. The tools and models developed in soft
matter physics to understand colloidal assembly offer some insights into the
problem of crystallizing proteins. This topical review describes the various
analogies that have been made between proteins and colloids in that context. We
highlight the explanatory power of patchy particle models, but also the
challenges of providing guidance for crystallizing specific proteins. We
conclude with a presentation of possible future research directions. This
article is intended for soft matter scientists interested in protein
crystallization as a self-assembly problem, and as an introduction to the
pertinent physics literature for protein scientists more generally.
