The three-dimensional structure of apo-NCS, as revealed by proton NMR, is based on an antiparallel seven-stranded beta-barrel. This fold is frequently encountered in protein structures, especially for immunoglobulin domains. The strands forming the barrel are joined by flexible loops of which three are implicated in the ligand binding site of these proteins. In this paper a preliminary comparison is given with respect to the static and dynamic properties of both the constant beta-barrel and the active loops for apo-NCS and the variable VH domain of an immunoglobulin Fab' fragment.