The phrase "important client of" is correct and usable in written English.
You can use it when you are describing a person or company that is an important client of yours. For example: "John Smith is an important client of mine."
Barclays has been an important client of Mr Bush's investment firm in Florida.
BlueMountain is an important client of ours, and we look forward to working with Jes in the future.
In addition, Goldman Sachs, where Mr. Corzine was co-chairman, is an important client of Mr. Bloomberg's company, Mr. Doctoroff said.
Weill allegedly helped get Grubman's children into a prestigious day care center in return for issuing a more favorable report on AT&T, a very important client of Salomon's investment-banking unit.
After Congo's Mobutu Sese Seko and the Philippines' Ferdinand Marcos, the latest fishy comedian to emerge as an important client of Swiss banks is the former Nigerian dictator, Sani Abacha.
Despite a reputation for offensive outbursts, Hayes was such an important client of Tullett Prebon, the firm Noel Cryan worked for, Mr Cryan claimed he felt he could not refuse Hayes' requests to help manipulate Libor lending rates for fear of being sacked, Southwark Crown Court has heard.
In the late eighties, True met the New York collectors Lawrence and Barbara Fleischman, who were important clients of Symes's and had been filling their East Side duplex with spectacular examples of classical art.
They are the "important" clients of the underwriting banks: the top pension funds, mutual funds, hedge funds, high net worth individuals, and long standing clients.
The most important clients of FSW were said to be merchants, students, truck drivers and public servants.
HER2, which is associated with poor prognosis in breast cancer, is one of the most important client proteins of HSP90, and HSP90 inhibitors have shown antitumor activity in an HER2-driven xenograft model [ 32].
The key molecule of this pathway, AKT, is also an important client protein of HSP90.
