Luton have made their ninth summer signing following the arrival of winger Danny Green.
Notts County have signed Togo international Mawouna Amevor on a two-year deal.
The 50-year-old, who is in his second spell in charge at the Stadio Atleti Azzurri d'Italia, had two years left to run on his existing deal.
A statement on the club's official website read: "Atalanta have reached a mutual agreement to prolong our working relationship with coach Stefano Colantuono until June 2016."
The former Palermo boss has guided Atalanta to 12th in the current league table with a return of 22 points from 19 games, ahead of Sunday's trip to Lazio.