A prominent local developer will build two towers next to Boston’s Christian Science Plaza, shaking up a signature open space with what will be one of the tallest buildings to hit the city skyline in years.

One tower will rise up to 50 stories, containing a hotel, condominiums, stores, and restaurants. The other will be about 20 stories and include apartments and additional retail space. The city has already approved the broad outlines of the project, and construction could begin by the end of this year.