Phosphorylation-dependent conformational changes induce a switch in the actin-binding function of MARCKS.
Phosphorylation of myristoylated alanine-rich protein kinase C substrate (MARCKS) by protein kinase C eliminates actin filament cross-linking activity, but residual filament binding activity docks phosphorylated MARCKS on filamentous actin. The postulated actin-binding region of MARCKS, which includes a Ca(2+)-calmodulin-binding site, has been portrayed with alpha-helical structure, analogous to other calmodulin-binding domains. Previous speculation suggested that MARCKS may dimerize to form the two functional actin-binding sites requisite for cross-linking activity. Contrary to these hypotheses, we show that MARCKS peptide with actin-cross-linking activity has an extended structure in aqueous solution but assumes a more compact structure upon phosphorylation. We hypothesize that structural changes in the MARCKS peptide induced by phosphorylation create a dynamic structure that, on average, has only one actin-binding site. Moreover, independent of the state of phosphorylation, this peptide is monomeric rather than dimeric, implying that two distinct actin-binding sites are responsible for the actin-cross-linking activity of unphosphorylated MARCKS. These studies uniquely elucidate the mechanism by which phosphorylation of MARCKS induces structural changes and suggest how these structural changes determine biological activity.
Bubb
M R
MR
Department of Medicine, University of Florida, Gainesville, Florida 32610, USA.
Lenox
R H
RH
Edison
A S
AS
D000595:Amino Acid Sequence; D047908:Intracellular Signaling Peptides and Proteins; D009682:Magnetic Resonance Spectroscopy; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D010766:Phosphorylation; D011485:Protein Binding; D011487:Protein Conformation; D011493:Protein Kinase C / Q000378:metabolism*; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D011506:Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D011493:Protein Kinase C