Quaker Steak & Lube, the Sharon-based restaurant chain, has filed for bankruptcy protection and said it expects to be acquired by TravelCenters of America for $25 million, the Pittsburgh Post-Gazette reported today. The deal calls for Quaker Steak, with 50-plus locations in the U.S., to retain its brand and possibly expand under the new owner. TravelCenters of America has more than 500 quick- and full-service restaurants in 43 states. TravelCenters has already made a deposit on the acquisition, the companies said, and agreed to offer jobs to “substantially all” of Quaker Steak’s current employees.