Mapping intramolecular distances of the 18.5-kDa Myelin Basic Protein under various conditions by Förster Resonance Energy Transfer
The predominant 18.5-kDa isoform of Myelin Basic Protein (MBP) is essential for the development of myelin in the central nervous system (CNS), and is hyper-deiminated in multiple sclerosis. We have previously obtained intramolecular distances between several single Cys-substituted sites in unmodified and pseudo-deiminated MBP variants, and a single internal Trp residue, by Förster Resonance Energy Transfer (FRET). I have obtained additional constraints by FRET of fluorophores attached to double- and single-Cys-substituted residues in the presence of dodecylphosphocholine (DPC) and Zn2+ (to mimic the myelin membrane per se). The quenching of Trp fluorescence by the acceptor showed that Zn2+ in the presence of DPC at its critical micelle concentration of 1.25 mM affected MBP’s local tertiary fold, but FRET distances indicated a negligible effect on global structure. We showed that DPC, like trifluoroethanol (TFE), caused slight compaction and extension. No significant differences between the two variants were seen.