Solution structure of a tethered Lmo2_LIM2/Ldb1_LID complex

Abstract

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 Ldb1 LID . The ordered regions of Ldb1 in this complex correspond well with binding hotspots previously defined by mutagenic studies. Comparisons of this Lmo2 LIM2 -Ldb1 LID structure with previously determined structures of the Lmo2/Ldb1 LID 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.

LMO2 Oncoprotein Stability in T-Cell Leukemia Requires Direct LDB1 Binding

“…We visualized I322 within available structures of an LMO2-LID fusion protein (PDB accession number 2XJZ) (Fig. 3B) (53)(54)(55) and found that it was in close proximity to LMO2 residues L64 and L71, suggesting a potential hydrophobic interface. L64 and L71 were both highly conserved in LMO2 paralogs, supporting an important functional role for these residues (Fig.…”

“…This was surprising since it was not predicted by the structural data on the LMO2/LDB1 interaction. The expression of fulllength recombinant LMO2 and LDB1 in bacteria has been technically challenging, but a fusion protein comprised of full-length LMO2 linked to the LID (i.e., LMO2-LID) was analyzed in solution and crystallized (53)(54)(55)57). Both nuclear magnetic resonance (NMR) and X-ray diffraction structures show binding of the LID in an extended conformation to both LIM domains of LMO2, where backbone contacts predominate between the LID and the NH 2 -terminal part of LMO2, with electrostatic interactions at the COOH terminus.…”

Conformational flexibility of the oncogenic protein LMO2 primes the formation of the multi-protein transcription complex

“…Our studies suggest that initially synthesized LMO2 protein is intrinsically disordered and that binding to a partner protein confers a configuration that nucleates subsequent protein complex formation. The structure of LMO2:LDB1-LID 36 49 , demonstrates a relatively flat, extended rod structure, able to “present” the LIM fingers to allow for other protein-protein interactions such as with GATA1 50 . By contrast, interaction with VH confers a distinct structure that renders LMO2 inactive due to inefficient binding of natural partners.…”

“…First, the use of single domain VH (or indeed scFv) to facilitate co-expression of otherwise intransigent proteins is likely to be a useful general strategy. Molecules like LMO2, that show significant intrinsic flexibility 52 49 , could be stabilized by binding with antibody fragments aided by the masking of hydrophobicity in the interaction with the VH interface.…”

Biochemical Feature of LMO2 Interactome and LMO2 Function Prospect

“…In this study, we found that LMO2 favored binding to peptides with β-sheet structure and relatively unstable confirmation. Moreover, LMO2 itself also reveals in some degree conformational flexibility that facilitates its interaction with other proteins [ 24 , 25 ]. Thus, it can be speculated that the structure feature of LMO2 itself and its preferred binding peptides benefits mutually to allow it the characteristic of a wide spectrum of protein interactome.…”