Cole J L, Carroll S S, Kuo L C
Department of Biological Chemistry, Merck Research Laboratories, West Point, Pennsylvania 19486, USA.
J Biol Chem. 1996 Feb 23;271(8):3979-81. doi: 10.1074/jbc.271.8.3979.
Ribonuclease L is an endoribonuclease that is activated by binding of 2',5'-linked oligoadenylates. Activation of ribonuclease L also induces dimerization. Here, we demonstrate using equilibrium sedimentation that dimerization requires the binding of one 5'-monophosphate 2',5'-(adenosine)3 molecule per ribonuclease L monomer. No dimerization was observed in the absence of activator up to a protein concentration of 18 microM, indicating that unliganded enzyme is unable to dimerize or the association is very weak. In parallel with dimerization, enzymatic activity is also maximized at a 1:1 activator: ribonuclease L stoichiometry. The same stoichiometry for dimerization is observed using a nonphosphorylated activator 2'-5'-(adenosine)3. Adenosine triphosphate or RNA oligonucleotide substrates do not induce dimerization. The observed stoichiometry supports a model for ribonuclease L dimerization in which activator binds to monomer, which subsequently dimerizes.
核糖核酸酶L是一种内切核糖核酸酶，通过与2',5'-连接的寡聚腺苷酸结合而被激活。核糖核酸酶L的激活还会诱导二聚化。在此，我们使用平衡沉降法证明，二聚化需要每个核糖核酸酶L单体结合一个5'-单磷酸2',5'-(腺苷)3分子。在不存在激活剂的情况下，直至蛋白质浓度达到18 microM时均未观察到二聚化，这表明未结合配体的酶无法二聚化或其缔合非常弱。与二聚化同时，酶活性在激活剂与核糖核酸酶L的化学计量比为1:1时也达到最大值。使用非磷酸化激活剂2'-5'-(腺苷)3时，观察到相同的二聚化化学计量比。三磷酸腺苷或RNA寡核苷酸底物不会诱导二聚化。观察到的化学计量比支持了核糖核酸酶L二聚化的模型，即激活剂与单体结合，随后单体二聚化。
