About FHL / Four and A Half LIM:
FHL-2, or four and a half LIM domains protein 2, is a protein that is encoded by the FHL2 gene in humans. The LIM domain is a strongly conserved double zinc finger motif found in LIM proteins.
FHL-2 is thought to play a role in extracellular membrane assembly and may act as a link between presenilin-2 and an intracellular signalling pathway.
Four and A Half LIM Structure
One of the members of the LIM-only protein family is the four-and-a-half LIM (FHL)-only protein subfamily. Protein members in the group may have descended from a common origin and share a high degree of amino acid sequence similarity. The presence of the four and a half cysteine-rich LIM homeodomains, with the half-domain often located at the N-terminus, distinguishes these proteins. The name LIM was derived from the first letter of the transcription factors LIN-11, ISL-1, and MEC-3, which were used to describe the domain.
There have been no reports of direct interactions between the LIM domain and DNA. Instead, comprehensive evidence suggests that FHL2 plays a functional role in promoting protein-protein interactions between LIM-containing proteins and their binding partners. So far, five members of the FHL subfamily have been identified: FHL1, FHL2, FHL3, FHL4, and activator of CREM in testis (ACT) in humans. FHL1, FHL2, and FHL3 are primarily expressed in muscle, whereas FHL4 and FHL5 are only expressed in the testis.
The well-known tumor suppressor protein p53, serum response factor specificity protein 1 are all transcription factors that have been implicated in the regulation of fhl2 expression (Sp1) IL-1, a pleiotropic factor, MEF-2, and activator protein-1 (AP-1). FHL2 is a transcription factor that regulates the expression of other genes in addition to being regulated by other transcription factors. FHL2 regulates transcription by acting as an adaptor protein that interacts with the targeted genes indirectly. In reality, the LIM domain serves as a scaffold for the assembly of multimeric protein complexes.