Transient α-helices in the disordered RPEL motifs of the serum response factor coactivator MKL1.

Abstract

The megakaryoblastic leukemia 1 (MKL1) protein functions as a transcriptional coactivator of the serum response factor. MKL1 has three RPEL motifs (RPEL1, RPEL2, and RPEL3) in its N-terminal region. MKL1 binds to monomeric G-actin through RPEL motifs, and the dissociation of MKL1 from G-actin promotes the translocation of MKL1 to the nucleus. Although structural data are available for RPEL motifs of MKL1 in complex with G-actin, the structural characteristics of RPEL motifs in the free state have been poorly defined. Here we characterized the structures of free RPEL motifs using NMR and CD spectroscopy. NMR and CD measurements showed that free RPEL motifs are largely unstructured in solution. However, NMR analysis identified transient α-helices in the regions where helices α1 and α2 are induced upon binding to G-actin. Proline mutagenesis showed that the transient α-helices are locally formed without helix-helix interactions. The helix content is higher in the order of RPEL1, RPEL2, and RPEL3. The amount of preformed structure may correlate with the binding affinity between the intrinsically disordered protein and its target molecule.

• Authors: Mineyuki Mizuguchi, Takahiro Fuju, Takayuki Obita, Mitsuru Ishikawa, Masaaki Tsuda, Akiko Tabuchi
• Journal: Scientific reports (Sci Rep) Vol. 4 Pg. 5224 (Jun 09 2014) ISSN: 2045-2322 [Electronic] England
• PMID: 24909411 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Actins
• DNA-Binding Proteins
• Serum Response Factor
• Trans-Activators

Topics

• Actins (chemistry, metabolism)
• Amino Acid Motifs (physiology)
• Cell Nucleus (metabolism)
• DNA-Binding Proteins (chemistry, metabolism)
• Magnetic Resonance Spectroscopy (methods)
• Protein Binding (physiology)
• Protein Structure, Secondary (physiology)
• Serum Response Factor (chemistry, metabolism)
• Trans-Activators (chemistry, metabolism)