Solution structure of a tethered Lmo2LIM2/Ldb1LID complex

LIM-only protein 2, Lmo2, is a regulatory protein that is essential for hematopoietic development and inappropriate overexpression of Lmo2 in T-cells contributes to T-cell leukemia. It exerts its functions by mediating protein-protein interactions and nucleating multicomponent transcriptional complexes. Lmo2 interacts with LIM domain binding protein 1 (Ldb1) through the tandem LIM domains of Lmo2 and the LIM interaction domain (LID) of Ldb1. Here, we present the solution structure of the LIM2 domain of Lmo2 bound to Ldb1LID. The ordered regions of Ldb1 in this complex correspond well with binding hotspots previously defined by mutagenic studies. Comparisons of this Lmo2LIM2-Ldb1LID structure with previously determined structures of the Lmo2/Ldb1LID complexes lead to the conclusion that modular binding of tandem LIM domains in Lmo2 to tandem linear motifs in Ldb1 is accompanied by several disorder-to-order transitions and/or conformational changes in both proteins.