Navaratnam N, Bhattacharya S, Fujino T, Patel D, Jarmuz A L, Scott J
Medical Research Council Molecular Medicine Group, Royal Postgraduate Medical School, Hammersmith Hospital, London, England.
Cell. 1995 Apr 21;81(2):187-95. doi: 10.1016/0092-8674(95)90328-3.
The site-specific C to U editing of apolipoprotein B100 (apoB100) mRNA requires a 27 kDa protein (p27) with homology to cytidine deaminase. Here, we show that p27 is a zinc-containing deaminase, which operates catalytically like the E. coli enzyme that acts on monomeric substrate. In contrast with the bacterial enzyme that does not bind RNA, p27 interacts with its polymeric apoB mRNA substrate at AU sequences adjacent to the editing site. This interaction is necessary for editing. RNA binding is mediated through amino acid residues involved in zinc coordination, in proton shuttling, and in forming the alpha beta alpha structure that encompasses the active site. However, certain mutations that inactivate the enzyme do not affect RNA binding. Thus, RNA binding does not require a catalytically active site. The acquisition of polymeric substrate binding provides a route for the evolution of this editing enzyme from one that acts on monomeric substrates.
载脂蛋白B100（apoB100）信使核糖核酸（mRNA）位点特异性的胞嘧啶（C）到尿嘧啶（U）的编辑需要一种与胞苷脱氨酶具有同源性的27千道尔顿（kDa）蛋白质（p27）。在此，我们证明p27是一种含锌脱氨酶，其催化作用类似于作用于单体底物的大肠杆菌酶。与不结合RNA的细菌酶相反，p27在编辑位点相邻的AU序列处与其聚合的apoB mRNA底物相互作用。这种相互作用对于编辑是必需的。RNA结合是通过参与锌配位、质子穿梭以及形成包含活性位点的αβ α结构的氨基酸残基介导的。然而，某些使该酶失活的突变并不影响RNA结合。因此，RNA结合不需要催化活性位点。聚合底物结合的获得为这种编辑酶从作用于单体底物的酶进化提供了一条途径。
