On the basis of comparative studies of known antibody structures and sequences 
it has been argued that there is a small repertoire of main-chain conformations 
for at least five of the six hypervariable regions of antibodies, and that the 
particular conformation adopted is determined by a few key conserved residues. 
These hypotheses are now supported by reasonably successful predictions of the 
structures of most hypervariable regions of various antibodies, as revealed by 
comparison with their subsequently determined structures.