A Deed of Trust has three parties. The first party is the trustor. This is the party that creates the trust, and is usually the borrower. The second party is the beneficiary of the trust, which is usually the lender. The third party is the trustee, who is usually an unrelated party, such as a title company, who holds the deed until the conditions of the trust have been satisfied.
It sounds like the assignment of the deed of trust means that the beneficiary of the deed of trust has been changed from MERS to Deutsche Bank. If that is the case, then it means that Deutsche Bank is the new beneficiary under the Deed of Trust. The new beneficiary has all of the rights of the original beneficiary, and if there are any problems or defect to title that the prior beneficiary had, then those problems or defects are now the responsibility of the new beneficiary.
I hope this clears things up for you.