  We interpret the newly discovered pentaquark $P_c(4450)$ as a bound state of
charmonium $\psi(2S)$ and the nucleon. The binding potential is due to
charmonium-nucleon interaction that in the heavy quark approximation is
proportional to the product of the charmonium chromoelectric polarizability and
the nucleon energy-momentum distribution. We use the large $N_c$ expansion to
estimate the quarkonium polarizability and calculate the nucleon properties in
the framework of the mean-field picture of light baryons. Two almost degenerate
states $J^P=(1/2)^-$ and $J^P=(3/2)^-$ are predicted at the position of the
$P_c(4450)$ pentaquark. We find that the nucleon-$\psi(2S)$ bound state has a
naturally narrow width in the range of tens of MeV. The unitary multiplet
partners of the $P_c(4450)$ pentaquark and the generalization to $b \bar
b$-nucleon pentaquark bound states are discussed.
