lxxll
LxxLL is a short linear motif defined by the amino acid sequence leucine–any amino acid–any amino acid–leucine–leucine (LxxLL). It functions as a nuclear receptor box found in a broad class of transcriptional coactivators that augment hormone receptor signaling. The motif is typically embedded in coactivator proteins and contributes to the formation of transcriptional activation complexes.
Mechanistically, the LxxLL motif binds to the ligand-binding domain of nuclear receptors. Binding is often ligand-dependent;
Occurrence and examples: The motif is common in steroid receptor coactivators, notably members of the p160/SRC
Significance and use in research: The LxxLL–nuclear receptor interaction is central to many hormone-responsive gene programs.
History: The concept of the NR box and the LxxLL motif emerged in the 1990s with the