N.M.R. studies on myelin basic protein. II. ¹H N.M.R. studies of the protein and constituent peptides in aqueous solutions

Abstract

¹H N.M.R. spectra (270 MHz) of myelin basic protein (MBP) at pD 3.7 in D₂O were obtained as a function of concentration and compared with computed spectra. Reduced line widths obtained for 0.5-mM samples and use of the convolution difference technique enabled detection of chemical shift heterogeneities for histidine, tyrosine, methionine, threonine, and isoleucine residues in the protein; this is indicative of secondary/tertiary structure. Chemical shift assignments were confirmed by the use of the Carr-Purcell A pulse sequence and selective decoupling as well as by correlation of the MBP spectrum with that of its constituent cathepsin D digest peptides. The methyl resonance from the unique methylated arginine-107 was found, and its chemical shift compared to that of N^G-monomethyl-L-arginine and the methylated arginine peak in the peptide fragment, residues 90-170. The absence of ring- current effects on the methyl chemical shift precludes conformations of MBP in which the methylarginine interacts with the phenylalanine pair at residues 89 and 90.