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 NG-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.