  $QQ^\prime qq\bar q$ pentaquarks are studied in a potential model, under the
hypothesis that they are composite objects of two diquarks and one antiquark.
The interaction between two colored objects includes two contributions, one
based on the $q\bar q$ potential in QCD, computed in the gauge/string duality
approach, and another describing the spin-spin interaction. The model has been
extended to investigate pentaquarks with different quark content, as $Qqqq\bar
q$ and $Qqqq\bar Q$, the latter including the states observed by LHCb,
$P_c(4380)^+$ and $P_c(4450)^+$, later updated, with a new data sample, to
$P_c(4312)^+$, $P_c(4440)^+$, and $P_c(4457)^+$.
