  A coarse-grained off-lattice model that is not biased in any way to the
native state is proposed to fold proteins. To predict the native structure in a
reasonable time, the model has included the essential effects of water in an
effective potential. Two new ingredients, the dipole-dipole interaction and the
local hydrophobic interaction, are introduced and are shown to be as crucial as
the hydrogen bonding. The model allows successful folding of the wild-type
sequence of protein G and may have provided important hints to the study of
protein folding.
