  Inspired by $P_c(4380)$ and $P_c(4450)$ recently observed by LHCb, a QCD sum
rule investigation is performed, by which they can be identified as exotic
hidden-charm pentaquarks composed of an anti-charmed meson and a charmed
baryon. Our results suggest that $P_c(4380)$ and $P_c(4450)$ have quantum
numbers $J^P=3/2^-$ and $5/2^+$, respectively. Furthermore, two extra
hidden-charm pentaqurks with configurations $\bar{D}\Sigma_c^*$ and
$\bar{D}^*\Sigma_c^*$ are predicted, which have spin-parity quantum numbers
$J^P=3/2^-$ and $J^P=5/2^+$, respectively. As an important extension, the mass
predictions of hidden-bottom pentaquarks are also given. Searches for these
partners of $P_c(4380)$ and $P_c(4450)$ are especially accessible at future
experiments like LHCb and BelleII.
