Gay AIDS activist Jonathan Perry has replaced Nobel Peace Prize nominee Zackie Achmat as the keynote speaker at an AIDS summit this Saturday at the Science Center.

The summit, entitled “Unite Against AIDS: HIV/AIDS in Africa and the African Diaspora” will bring together college and high school students to examine the HIV/AIDS crisis and inspire youth to combat the disease.

According to his website, Perry, a graduate of the historically black college Johnson C. Smith University, was the first openly gay, black, HIV-positive student at his school. He was also the founder of Johnson C. Smith University’s first official gay, lesbian, bisexual, and transgender organization.

“He encompasses a lot of the different types of people we are trying to reach out to,” said Sarika P. Bansal ’06, one of the summit’s committee members.

Summit organizers chose Perry to be the replacement speaker soon after getting word that Achmat had suffered a heart attack at the end of March, Bansal said.

“[Achmat’s] prognosis is good, he is doing well, but [his assistant said] he would not be able to travel to Boston from South Africa,” Bansal said.

But organizers said they were not thwarted by the disappointing news.

“We were fortunate enough that the day when we were meeting to talk about [a replacement for] Zackie Achmat, [Perry’s] people called us,” said Jacob H. Bor ’05, another committee member of the summit. “They said he was interested in getting involved.”

The Unite Against AIDS Summit is a collaborative effort of the Black Men’s Forum, Harvard AIDS Coalition, Harvard African Students’ Association, and Harvard Concert Commission.