LOS ANGELES — Wilshire Grand Center, an estimated $1.2 billion mixed-use project in downtown Los Angeles, promises many things upon its 2017 completion date.

At 1,100 feet, it will be the tallest building west of the Mississippi, with technology features like those to protect against earthquakes. Most notably, the center will provide this city with its first new tower-based office space in about 20 years.

Yet, there is one potential feature of the project, unstated in any brochure, that looms large in the minds of downtown’s many champions: Wilshire Grand could catalyze more growth and diverse interest in the office market, long the troubled sector of real estate in downtown’s revitalization efforts.

The office space vacancy rate in downtown Los Angeles was 18.4 percent in the third quarter, according to a report from Cushman & Wakefield. This puts it above the national office vacancy rate, which is about 16 percent, according to data from Reis, a commercial real estate research firm.