Induced Secondary Structure and Polymorphism in an Intrinsically Disordered Structural Linker of the CNS: Solid-State NMR and FTIR Spectroscopy of Myelin Basic Protein Bound to Actin

• Published in: Biophysical journal Vol. 96; no. 1; pp. 180 - 191
• Main Authors: Ahmed, Mumdooh A.M., Bamm, Vladimir V., Shi, Lichi, Steiner-Mosonyi, Marta, Dawson, John F., Brown, Leonid, Harauz, George, Ladizhansky, Vladimir
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 07-01-2009; Biophysical Society; The Biophysical Society
• Subjects: Actin Cytoskeleton - chemistry; Actins - chemistry; Amino Acid Sequence; Animals; Assembly; Biophysics; Bundles; Central nervous system; Chickens; Cytoskeleton; Fourier transforms; Membranes; Mice; Molecular Sequence Data; Myelin; Myelin Basic Protein - chemistry; Myelin Basic Protein - genetics; Nuclear magnetic resonance; Nuclear Magnetic Resonance, Biomolecular - methods; Polymorphism; Protein; Protein Isoforms - chemistry; Protein Structure, Secondary; Proteins; Protons; Recombinant Proteins - chemistry; Salts - chemistry; Spectroscopy; Spectroscopy, Fourier Transform Infrared - methods; Spectrum analysis; Temperature
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/j.bpj.2008.10.003

The 18.5 kDa isoform of myelin basic protein (MBP) is a peripheral membrane protein that maintains the structural integrity of the myelin sheath of the central nervous system by conjoining the cytoplasmic leaflets of oligodendrocytes and by linking the myelin membrane to the underlying cytoskeleton whose assembly it strongly promotes. It is a multifunctional, intrinsically disordered protein that behaves primarily as a structural stabilizer, but with elements of a transient or induced secondary structure that represent binding sites for calmodulin or SH3-domain-containing proteins, inter alia. In this study we used solid-state NMR (SSNMR) and Fourier transform infrared (FTIR) spectroscopy to study the conformation of 18.5 kDa MBP in association with actin microfilaments and bundles. FTIR spectroscopy of fully
13C,
15N-labeled MBP complexed with unlabeled F-actin showed induced folding of both protein partners, viz., some increase in
β-sheet content in actin, and increases in both
α-helix and
β-sheet content in MBP, albeit with considerable extended structure remaining. Solid-state NMR spectroscopy revealed that MBP in MBP-actin assemblies is structurally heterogeneous but gains ordered secondary structure elements (both
α-helical and
β-sheet), particularly in the terminal fragments and in a central immunodominant epitope. The overall conformational polymorphism of MBP is consistent with its in vivo roles as both a linker (membranes and cytoskeleton) and a putative signaling hub.