LMO2 (LIM domain only 2) is a member of the LIM-only (LMO) family of LIM domain-containing transcriptional cofactors. LIM domains are 55-residue cysteine-rich structural units composed of two zinc fingers linked by a two amino-acid residue hydrophobic linker. LIM domain-containing proteins are believed to play crucial roles in many essential cellular processes such as cell growth, trafficking, cytoskeletal organization, differentiation and apoptosis (Zheng & Zhao, 2007
; Bach, 2000
) by mediating protein–protein interactions through their zinc-finger domains. Specifically, the presence of a tandem of LIM domains in the LMO proteins confers on them the potential to engage in multiple protein–protein interactions.
LMO2 is a 158-amino-acid nuclear protein composed of two LIM domains and a small N-terminal transactivation domain. LMO2 plays a central role in haematopoietic stem-cell development, erythropoiesis and angiogenesis (Warren et al.
; Yamada et al.
; Yamada et al.
). Upon chromosomal translocations or biallelic transcriptional activation, its ectopic expression is involved in the pathogenesis of T-cell acute lymphoblastic leukaemia (T-ALL; Boehm et al.
; Ferrando et al.
). In normal haematopoiesis, LMO2 interacts with the ubiquitously expressed protein Ldb1 [also known as CLIM (LIM homeobox protein cofactor) or NLI (nuclear LIM-domain interactor)]. Ldb1 comprises a 39-amino-acid C-terminal LIM-interaction domain (LID) that mediates interaction with all LMO proteins and LIM homeodomains (Jurata & Gill, 1997
; Kadrmas & Beckerle, 2004
) and an N-terminal dimerization domain (Jurata & Gill, 1997
) that allows the formation of higher order protein complexes. Indeed, the LMO2:Ldb1 complex acts as a scaffolding protein and participates in the assembly of a DNA-binding multiprotein complex that includes transcriptional regulators such as SCL, E2A and GATA-1 (Lecuyer et al.
; Schlaeger et al.
; Wadman et al.
). When abnormally expressed, similar protein complexes are believed to be involved in tumorigenesis in T-ALL (Grutz et al.
; Herblot et al.
; Ono et al.
). Interestingly, a role for LMO2 in B-cell lymphomas (Natkunam et al.
) and prostate cancer (Ma et al.
) has also been reported. Consequently, LMO2 has become a very attractive anticancer drug target. Efforts are currently focused on designing peptides and/or intrabodies that are able to disrupt transcriptional complexes containing LMO2 (Nam et al.
; Appert et al.
NMR structures of the N-terminal LIM domains of LMO4 and LMO2 in complex with the Ldb1 LID domain (Ldb1-LID; PDB codes 1j2o
, respectively; Deane et al.
) provided the first examples of LIM:Ldb1-LID complexes and highlighted the residues responsible for the interactions of the N-terminal LIM domains. The structure of both LIM domains of LMO4 fused to Ldb1-LID has also been solved by X-ray crystallography (LMO4:Ldb1-LID; PDB code 1rut
; Deane et al.
); however, the structure of the two-LIM-domain LMO2 in complex with Ldb1-LID has not been reported to date. Despite their 46% sequence identity, LMO2 and LMO4 have different functions and binding partners and bind Ldb1 with different affinities (Ryan et al.
). In order to obtain insights into the mechanism of action of LMO2 and to detail its binding interface with the Ldb1-LID domain, we set out to solve the structure of the LMO2:Ldb1-LID complex. Here, we report its production, crystallization and preliminary diffraction analysis.