In vitro dimerization of human RIO2 kinase

RIO proteins form a conserved family of atypical protein kinases. RIO2 is a serine/threonine protein kinase/ATPase involved in pre-40S ribosomal maturation. Current crystal structures of archaeal and fungal Rio2 proteins report a monomeric form of the protein. Here, we describe three atomic structures of the human RIO2 kinase showing that it forms a homodimer <i>in vitro</i>. Upon self-association, each protomer ATP-binding pocket is partially remodelled and found in an apostate. The homodimerization is mediated by key residues previously shown to be responsible for ATP binding and catalysis. This unusual <i>in vitro</i> protein kinase dimer reveals an intricate mechanism where identical residues are involved in substrate binding and oligomeric state formation. We speculate that such an oligomeric state might be formed also <i>in vivo</i> and might function in maintaining the protein in an inactive state and could be employed during import.

RIO蛋白（RIO proteins）是一类保守的非典型蛋白激酶家族。RIO2是一种参与pre-40S核糖体成熟过程的丝氨酸/苏氨酸蛋白激酶/ATP酶。目前已报道的古菌与真菌Rio2蛋白的晶体结构均显示该蛋白以单体形式存在。本研究解析了三个人源RIO2激酶的原子分辨率结构，揭示其在体外（in vitro）可形成同源二聚体。当发生自身组装时，每个原聚体的ATP结合口袋会发生部分重塑，并呈现无配体构象。该同源二聚化过程由此前被证实参与ATP结合与催化的关键残基所介导。这种罕见的体外蛋白激酶二聚体揭示了一种复杂的调控机制：相同的残基同时参与底物结合与寡聚体状态的形成。我们推测，此类寡聚体状态在体内（in vivo）也可能存在，其功能或为维持该蛋白处于失活状态，且可能在蛋白导入过程中发挥作用。