Plasticity of secondary structure in the N-terminal region of beta-dystroglycan

The secondary structure content of the N-terminal extracellular domain of beta-dystroglycan (a recombinant fragment extending from positions 654 to 750) has been quantitatively determined by means of CD and FTIR spectroscopies. The elements of secondary structure, namely an 8-10 residue long alpha-helix (10%) and two beta-strands (24%) have been assigned to specific amino acid sequences by means of a GOR constrained prediction method. The remaining 66% of the whole sequence is classified as turns or unordered. The temperature dependence of CD and FTIR spectra has been investigated in detail. A reversible, non-cooperative thermal transition is observed with both CD and FTIR spectroscopies up to 95 degrees C. The profile of the transition is typical of the unfolding of isolated peptides and corresponds to the progressive loss of the secondary structure elements of the protein with no evidence for collapsing phenomena, typical of globular proteins, upon heating.