INFO=($(MYSQL_PWD=`cat /etc/psa/.psa.shadow` mysql -uadmin psa -sN -e'SELECT h.www_root,s.login FROM domains d, hosting h, sys_users s WHERE s.id=h.sys_user_id AND h.dom_id=d.id AND d.name="example.com"')); chown -R ${INFO[1]}:psacln ${INFO[0]}; chown ${INFO[1]}:psaserv ${INFO[0]}

Starting from Plesk 17.8 it can be done easier

plesk repair fs example.com