Structured functional domains of myelin basic protein: cross talk between actin polymerization and Ca(2+)-dependent...

Area of Science:

• Neuroscience
• Biochemistry
• Structural Biology

Background:

• Myelin basic protein (MBP) is crucial for myelin sheath structure and function.
• MBP is intrinsically disordered but contains regions that form amphipathic alpha-helices.
• These helical regions mediate interactions with cytoskeletal proteins, calmodulin, and membranes.

Purpose of the Study:

• To further characterize the structure-function relationship of three key domains within MBP.
• To investigate the interactions of specific MBP peptide fragments with actin and Ca(2+)-activated calmodulin (Ca(2+)-CaM).
• To elucidate the role of these domains in protein-protein and protein-membrane interactions.

Main Methods:

• Construction of three recombinant MBP peptides (α1, α2, α3) corresponding to helical domains.
• Biophysical characterization using circular dichroism, isothermal titration calorimetry, and NMR spectroscopy.
• Assessment of interactions with actin (polymerization, bundling) and Ca(2+)-CaM, including CaM-induced effects.

Main Results:

• All three MBP peptides intrinsically adopt alpha-helical structures in aqueous solution.
• Peptides α1 and α3 bind strongly to Ca(2+)-CaM, adopting helical conformations; α3 binding is more dynamic.
• Only the α1 peptide promotes actin polymerization and bundling; Ca(2+)-CaM addition causes depolymerization of α1-induced actin polymers.

Conclusions:

• MBP possesses an N-terminal Ca(2+)-CaM binding domain, in addition to the known C-terminal site.
• This N-terminal domain is sufficient for CaM-induced actin depolymerization.
• The three characterized MBP domains function as molecular recognition fragments involved in membrane and protein associations.