SASCO MORTGAGE LOAN PURCHASE AGREEMENT

THIS SASCO MORTGAGE LOAN PURCHASE AGREEMENT, dated as of February 1, 2007 (the “ Agreement ”), is made and entered into between Thornburg Mortgage Funding, Inc., a Delaware corporation (the “ Seller ”), and Structured Asset Securities Corporation, a Delaware corporation (the “ Purchaser ”).

WHEREAS, effective with the execution of the TMFI Mortgage Loan Purchase Agreement dated as of February 1, 2007 (the “TMFI Purchase Agreement”) between Thornburg Mortgage Home Loans, Inc. (the “Initial Seller”) as seller, and the Seller, as purchaser, the Seller, as of the Closing Date, is the owner of the notes or other evidence of indebtedness (the “ Mortgage Notes ”) so indicated on Schedule I hereto referred to below, and the other documents or instruments constituting the Mortgage File (collectively, the “ Mortgage Loans ”) and, as a consequence thereof, the Seller owns the mortgages or deeds of trust (the “ Mortgages ”) on the related properties (the “ Mortgaged Properties ”) securing such Mortgage Loans, including rights to (a) any property acquired by foreclosure or deed in lieu of foreclosure or otherwise, (b) the proceeds of any insurance policies covering the Mortgage Loans or the Mortgaged Properties or the obligors on the Mortgage Loans and (c) the Seller’s security interest in any Additional Collateral; and

WHEREAS, effective with the execution of the TMFI Mortgage Loan Purchase Agreement, the Initial Seller, as of the Closing Date, has assigned to the Seller all its rights and interest under the servicing agreements identified on Schedule II hereto (each a “ Servicing Agreement ,” and together the “ Servicing Agreements ”), other than any servicing rights retained pursuant to the provisions of the Servicing Agreements, but only to the extent such rights relate to the servicing of the Mortgage Loans (the “ Contractual Rights ”); and

WHEREAS, the parties hereto desire that the Seller sell the Mortgage Loans, the Mortgages and related assets referred to above, assign the Contractual Rights and assign its rights with respect to the representations and warranties of the Initial Seller and remedies for breach pursuant to the TMFI Purchase Agreement (such rights and remedies, the “ TMFI Contractual Rights ”) to the Purchaser pursuant to the terms of this Agreement; and

WHEREAS, the Seller understands that the Purchaser, simultaneously with the execution of this Agreement, intends to transfer and assign all of its rights, title and interests in and to the Mortgage Loans, the Mortgages and the related assets, the Contractual Rights and the TMFI Contractual Rights to Thornburg Mortgage Securities Trust 2007-1 (the “ Trust ”) pursuant to the terms of that certain Sale and Servicing Agreement (the “ Sale and Servicing Agreement”) dated as of February 1, 2007 by and among the Trust, as issuer (the “ Issuer ”), the Purchaser, as depositor (in such capacity, the “ Depositor ”), the Seller, the Initial Seller, Wells Fargo Bank, N.A., as master servicer and securities administrator, and LaSalle Bank, National Association, as indenture trustee (the “ Indenture Trustee ”), and the Seller has agreed to perform certain obligations under this Agreement to accommodate such transfer and assignment; and

WHEREAS, the Issuer intends to pledge the Mortgage Loans, the Mortgages and related assets, the Contractual Rights and the TMFI Contractual Rights to the Indenture Trustee pursuant to an Indenture dated as of February 1, 2007 (the “ Indenture ”) between the Issuer and the Indenture Trustee, pursuant to which the Issuer shall issue its Mortgage-Backed Notes, Series 2007-1 (the “ Notes ”), the payment of which is to be secured by such pledged assets.

NOW, THEREFORE, in consideration of the mutual covenants herein contained and other good and valuable consideration, the receipt and adequacy of which are hereby acknowledged, the parties hereto agree as follows:

Section 1.01.   Definitions .   Any capitalized term used but not defined herein shall have the meaning assigned thereto in the Sale and Servicing Agreement and the Indenture.

Section 2.01.   Sale of Mortgage Loans; Assignment of the Contractual Rights and the TMFI Contractual Rights .   The Seller, concurrently with the execution and delivery of this Agreement, does hereby sell, assign, set over, and otherwise convey to the Purchaser, without recourse, all of its right, title and interest in, to and under (i) each Mortgage Loan, including the related Cut-Off Date Principal Balance, and all collections in respect of interest and principal due after the Cut-Off Date (and all principal received before the Cut-Off Date to the extent such principal relates to a Monthly Payment due after the Cut-Off Date); (ii) property which secured such Mortgage Loan and which has been acquired by foreclosure or deed in lieu of foreclosure; (iii) its interest in any insurance policies in respect of the Mortgage Loans; (iv) any Additional Collateral with respect to the Mortgage Loans; and (v) all proceeds of any of the foregoing.

Concurrently with the execution and delivery of this Agreement, the Seller hereby assigns to the Purchaser the Contractual Rights and the TMFI Contractual Rights. The Purchaser hereby accepts such assignment, and shall be entitled to exercise such Contractual Rights under each Servicing Agreement and such TMFI Contractual Rights as if the Purchaser had been a party to each such Servicing Agreement and the TMFI Purchase Agreement, respectively.

Section 2.02.   Obligations of the Seller Upon Sale and Assignment .   In connection with the transfer and assignment pursuant to Section 2.01 hereof, the Seller further agrees, at its own expense, on or prior to the Closing Date, (a) to indicate in its books and records that the Mortgage Loans have been sold to the Purchaser pursuant to this Agreement and (b) to deliver to the Purchaser and the Indenture Trustee, a computer file containing a true and complete list of all such Mortgage Loans specifying for each such Mortgage Loan, as of the Cut-Off Date, (i) its account number and (ii) the Cut-Off Date Principal Balance and such file, which forms a part of Schedule A to the Sale and Servicing Agreement, shall also be marked as Schedule I to this Agreement and is hereby incorporated into and made a part of this Agreement.

In connection with such conveyance by the Seller, the Seller shall on behalf of the Purchaser and the Issuer cause the Initial Seller to deliver to, and deposit with the Indenture Trustee (or its custodian), on or before the Closing Date, the documents described in Section 2.01 of the Sale and Servicing Agreement including, but not limited to, the Mortgage File, the Servicing Agreements and a copy of the TMFI Purchase Agreement. In the case of the Mortgage Loans (if any) that have been prepaid in full after the Cut-off Date and prior to execution of this Agreement, the Seller, in lieu of causing the Initial Seller to deliver the related Mortgage Files, shall cause the Initial Seller to deliver to the Purchaser an Officer’s Certificate which shall include a statement to the effect that all amounts received in connection with such prepayments that are required to be deposited in the Collection Account pursuant to Section 2.01 of the Sale and Servicing Agreement have been so deposited.

The Seller hereby confirms to the Purchaser that it has made the appropriate entries in its general accounting records, to indicate that the Mortgage Loans have been transferred as directed by the Purchaser.

The Purchaser hereby acknowledges its acceptance of all rights, title and interests in, to and under the Mortgage Loans and other property, the Contractual Rights and the TMFI Contractual Rights, now existing or hereafter created, conveyed to it pursuant to Section 2.01 hereof.

The parties hereto intend that the transaction set forth herein be a non-recourse sale by the Seller to the Purchaser of all of the Seller’s rights, title and interests in, to and under the Mortgage Loans and other property described in Section 2.01. Nonetheless, in the event the transaction set forth herein is deemed not to be a sale, the Seller hereby grants to the Purchaser a security interest in all of the Seller’s rights, title and interests in, to and under the Mortgage Loans and other property described in Section 2.01, whether now existing or hereafter created, to secure all of the Seller’s obligations hereunder; and this Agreement shall constitute a security agreement under applicable law. The Seller and the Purchaser shall, to the extent consistent with this Agreement, take such actions as may be necessary to ensure that, if this Agreement were deemed to create a security interest in the Mortgage Loans, the Contractual Rights and the TMFI Contractual Rights, such security interest would be deemed to be a perfected security interest of first priority under applicable law and will be maintained as such throughout the term of the Indenture.

Section 2.03.   Payment of Purchase Price for the Mortgage Loans .   In consideration of the sale of the Mortgage Loans, the related assets, the Contractual Rights and the TMFI Contractual Rights from the Seller to the Purchaser on the Closing Date, the Purchaser agrees to pay to the Seller on the Closing Date by transfer of immediately available funds, an amount equal to $1,475,654,383.67 (which amount includes accrued interest) (the “ Purchase Price ”). The Seller shall pay, and be billed directly for, all reasonable expenses incurred by the Purchaser or the Issuer in connection with the issuance of the Notes, including, without limitation, printing fees incurred in connection with the Preliminary Prospectus Supplement, the Final Prospectus Supplement and the Memorandum relating to the Notes, fees and expenses of Purchaser’s counsel, fees of the rating agencies requested to rate the Notes, accountant’s fees and expenses and the fees and expenses of the Trustee and other out-of-pocket costs, if any.

Section 3.01.   Representations and Warranties Relating to the Mortgage Loans .   In addition to the assignment of the TMFI Contractual Rights, the Seller hereby makes the representations and warranties set forth in Schedule III hereto applicable to the Mortgage Loans and by this reference incorporated herein, as of the Closing Date.

Section 3.02.     Seller’s Representations and Warranties .   The Seller represents, warrants and covenants to the Purchaser as of the Closing Date or as of such other date specifically provided herein:

(i)   the Seller is duly organized, validly existing and in good standing as a corporation under the laws of the State of Delaware and is and will remain in compliance with the laws of each state in which any Mortgaged Property is located to the extent necessary to fulfill its obligations hereunder;

(ii)   the