A U.S. regulator sued Bank of New York Mellon Corp (BK.N) on Wednesday over $2.06 billion in residential mortgage-backed securities purchased by a failed Texas bank, and accused it of breaching its duties as bond trustee to protect investors. In a complaint filed in Manhattan federal court, the Federal Deposit Insurance Corp, which sued in its capacity as receiver for the former Guaranty Bank, said it suffered more than $440 million in losses when it sold the securities in March 2010.