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

The secondary structure content of the N-terminal extracellular domain of b eta -dystroglycan (a recombinant fragment extending from positions 654 to 7 50) has been quantitatively determined by means of CD and FTIR spectroscopi es. The elements of secondary structure, namely an 8-10 residue long alpha -helix (10%) and two beta -strands (24%) have been assigned to specific ami no acid sequences by means of a GOR constrained prediction method. The rema ining 66% of the whole sequence is classified as turns or unordered. The te mperature 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 degreesC. The profile of the transition i s typical of the unfolding of isolated peptides and corresponds to the prog ressive loss of the secondary structure elements of the protein with no evi dence for collapsing phenomena, typical of globular proteins, upon heating. (C) 2001 Elsevier Science B.V. All rights reserved.