  Two proteins, one belonging to the mainly alpha class and the other belonging
to the alpha/beta class, are selected to test a kinetic mechanism for protein
folding. Targeted molecular dynamics is applied to generate folding pathways
for those two proteins, starting from two well defined initial conformations: a
fully extended and a alpha-helical conformation. The results show that for both
proteins the alpha-helical initial conformation provides overall lower energy
pathways to the native state. For the alpha/beta protein, 30 % (40%) of the
pathways from an initial alpha-helix (fully extended) structure lead to
unentangled native folds, a success rate that can be increased to 85 % by the
introduction of a well-defined intermediate structure. These results open up a
new direction in which to look for a solution to the protein folding problem,
as detailed at the end.
