IDPs and IDRs in biomolecular condensates

Over the last decade, there has been considerable interest in the role of intrinsically disordered proteins and protein regions in the formation of nonstoichiometric assemblies. These assemblies have been given various names, including membraneless organelles and biomolecular condensates, and their formation is often described as a biological phase transition. Given that some of these assemblies are highly dynamic and undergo dripping, wetting, and fusion, the physics of liquid-liquid phase separation have been invoked as a putative mechanism for assembly formation and maintenance. In this chapter, we first introduce some general background on biological phase separation and then consider how IDRs may mediate this phenomenon. We will focus on in vitro systems for which sequence effects have been explicitly examined while considering the caveats and limitations of projecting in vitro observations to in vivo phenomena. We finish by considering some additional biophysical and functional topics that have been discussed less explicitly elsewhere.