The Securities and Exchange Commission reached a $550 million settlement with Goldman Sachs Group that will resolve its lawsuit against the firm alleging it misled investors in a subprime mortgage product, the agency announced Thursday.

The SEC sued Goldman in April, charging it with fraud in marketing of a complex financial product called Abacus 2007-AC1 that was based on mortgage-backed securities.

In agreeing to the SEC’s largest-ever penalty paid by a Wall Street firm, Goldman acknowledged that its marketing materials for the product contained incomplete information, the SEC said.

Goldman denied any wrongdoing in the SEC lawsuit but has been under pressure from shareholders to reach a settlement on the fraud lawsuit and other SEC probes.

The firm faced a Monday deadline to file a response to the lawsuit, which accuses the firm of selling the collateralized debt obligation (CDO) without disclosing to other participants in the deal that hedge-fund firm Paulson & Co. helped select some of the underlying mortgage securities and was betting on the financial instrument’s decline.

Settlement papers filed in a New York court contained the following statement from Goldman: “It was a mistake for the Goldman marketing materials to state that the reference portfolio was ‘selected by’ ACA Management LLC without disclosing the role of Paulson & Co. Inc. in the portfolio selection process and that Paulson’s economic interests were adverse to CDO investors. Goldman regrets that the marketing materials did not contain that disclosure.”

“This settlement is a stark lesson to Wall Street firms that no product is too complex, and no investor too sophisticated, to avoid a heavy price if a firm violates the fundamental principles of honest treatment and fair dealing,” said Robert Khuzami, director of the SEC’s Division of Enforcement.

Shares of Goldman Sachs ended 4.4 percent higher at $145.22 on Thursday, and it continued to climb in after-hours trade, recently at $151.57.