The first LIM domain of Ajuba-like proteins: Ajuba like LIM protein family includes three highly homologous proteins Ajuba, Limd1, and WTIP. Members of the family contain three tandem C-terminal LIM domains and a proline-rich N-terminal region. This family of proteins functions as scaffolds, participating in the assembly of numerous protein complexes. In the cytoplasm, Ajuba binds Grb2 to modulate serum-stimulated ERK activation. Ajuba also recruits the TNF receptor-associated factor 6 (TRAF6) to p62 and activates PKCKappa activity. Ajuba interacts with alpha-catenin and F-actin to contribute to the formation or stabilization of adheren junctions by linking adhesive receptors to the actin cytoskeleton. Although Ajuba is a cytoplasmic protein, it can shuttle into the nucleus. In nucleus, Ajuba functions as a corepressor for the zinc finger-protein Snail. It binds to the SNAG repression domain of Snail through its LIM region. Arginine methyltransferase-5 (Prmt5), a protein in the complex, is recruited to Snai l through an interaction with Ajuba. This ternary complex functions to repress E-cadherin, a Snail target gene. In addition, Ajuba contains functional nuclear-receptor interacting motifs and selectively interacts with retinoic acid receptors (RARs) and rexinoid receptor (RXRs) to negatively regulate retinoic acid signaling. Wtip, the Wt1-interacting protein, was originally identified as an interaction partner of the Wilms tumour protein 1 (WT1). Wtip is involved in kidney and neural crest development. Wtip interacts with the receptor tyrosine kinase Ror2 and inhibits canonical Wnt signaling. LIMD1 was reported to inhibit cell growth and metastases. The inhibition may be mediated through an interaction with the protein barrier-to-autointegration (BAF), a component of SWI/SNF chromatin-remodeling protein; or through the interaction with retinoblastoma protein (pRB), resulting in inhibition of E2F-mediated transcription, and expression of the majority of genes with E2F1- responsive elements. Recently, Limd1 was shown to interact with the p62/sequestosome protein and influence IL-1 and RANKL signaling by facilitating the assembly of a p62/TRAF6/a-PKC multi-protein complex. The Limd1-p62 interaction affects both NF-kappaB and AP-1 activity in epithelial cells and osteoclasts. Moreover, LIMD1 functions as tumor repressor to block lung tumor cell line in vitro and in vivo. Recent studies revealed that LIM proteins Wtip, LIMD1 and Ajuba interact with components of RNA induced silencing complexes (RISC) as well as eIF4E and the mRNA m7GTP cap-protein complex and are required for microRNA-mediated gene silencing. As in other LIM domains, this domain family is 50-60 amino acids in size and shares two characteristic zinc finger motifs. The two zinc fingers contain eight conserved residues, mostly cysteines and histidines, which coordinately bond to two zinc atoms. LIM domains function as adaptors or scaffolds to support the assembly of multimeric protein.
Comment: The two zinc fingers contain eight conserved residues, mostly cysteines and histidines, which coordinately bond to two zinc atoms. The Zn binding residues of LIM domain are highly conserved.
Jiyao W et al.(2023). "The conserved domain database in 2023.",