Keeping them all together: β-propeller domains in histone methyltransferase complexes

Histone methyltransferases (HKMTs) residing in multi-subunit protein complexes frequently require the presence of β-propeller proteins to achieve their biological functions. Recent biochemical studies have highlighted the functional diversity of these scaffolding proteins in maintaining the integrity of the complexes, allosterically regulating HKMT enzymatic activity and acting as "histone tethering devices" to facilitate the interaction between HKMTs and their substrates. Structural studies have revealed that, while β-propeller domain proteins share structural similarity, they employ divergent mechanisms to achieve their functions. This review focuses on the progress made in the last decade to identify the biochemical determinants underlying the functions of these important proteins.