1ylg

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NMR structure of the apoB mRNA stem-loop and its interaction with the C to U editing APOBEC1 complementary factor

Overview

We have solved the NMR structure of the 31-nucleotide (nt) apoB mRNA, stem-loop, a substrate of the cytidine deaminase APOBEC1. We found that, the edited base located at the 5' end of the octa-loop is stacked between, two adenosines in both the unedited (cytidine 6666) and the edited, (uridine 6666) forms and that the rest of the loop is unstructured. The, 11-nt "mooring" sequence essential for editing is partially flexible, although it is mostly in the stem of the RNA. The octa-loop and the, internal loop in the middle of the stem confer this flexibility. These, findings shed light on why APOBEC1 alone cannot edit efficiently the, cytidine 6666 under physiological conditions, the editing base being, buried in the loop and not directly accessible. We also show that APOBEC1, does not specifically bind apoB mRNA and requires the auxiliary factor, APOBEC1 complementary factor (ACF), to edit specifically cytidine 6666., The binding of ACF to both the mooring sequence and APOBEC1 explains the, specificity of the reaction. Our NMR study lead us to propose a mechanism, in which ACF recognizes first the flexible nucleotides of the mooring, sequence (the internal loop and the 3' end octa-loop) and subsequently, melts the stem-loop, exposing the amino group of the cytidine 6666 to, APOBEC1. Thus, the flexibility of the mooring sequence plays a central, role in the RNA recognition by ACF.

About this Structure

1YLG is a Single protein structure of sequence from [1]. Full crystallographic information is available from OCA.

Reference

NMR structure of the apoB mRNA stem-loop and its interaction with the C to U editing APOBEC1 complementary factor., Maris C, Masse J, Chester A, Navaratnam N, Allain FH, RNA. 2005 Feb;11(2):173-86. PMID:15659357

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