Lawmakers ultimately killed the legislation, and a House Ethics Committee review of Turner's actions found no wrongdoing.
But Bosma said Turner's efforts on the legislation were troublesome and announced that he would remove Turner from leadership following November's elections.
"Any involvement in the decision-making process, whether in public debate or through private discussions with fellow elected officials, presented an irreconcilable conflict," Bosma said in a statement. "Turner should have recused himself entirely from influencing the matter in any way given the personal financial stake involved."
Mainstreet — which is owned by Turner, his family and a small group of other investors — builds nursing homes throughout Indiana. Lawmakers, spurred by concerns raised from other nursing home owners that the market was being flooded, considered banning new construction.
Turner didn't disclose the extent of his financial interest either in public filings or when lobbying his House colleagues.
The Turner business model included selling homes to a Canadian company run by his son, Zeke Turner, at sizable profits. Mainstreet executives announced earlier this month that they were selling the Canadian company to an Ohio-based real estate company for $2.4 billion.
The sale reignited calls from critics — including Turner's Democratic opponent in the November election, Bob Ashley — for a new ethics investigation.
Turner did not address his interest in the company or express any disappointment in a sparsely-worded statement Friday.
"I serve at the pleasure of the Speaker of the House and respect his decision for the next term," he said. "I look forward to continuing as a member of the Indiana House of Representatives and serving the citizens of my district."
Democrats, including Ashley and Democratic Party Chairman John Zody, praised Bosma's decision. But Zody added that it does not address what he said is an overall "culture of corruption" at the Statehouse.
Bosma said he had consulted with House and Senate lawmakers and would be pushing for ethics reforms in the upcoming session.
"I have no doubt the House Ethics Committee review of this matter was thorough and resulted in the correct conclusion; however, it also revealed significant gaps which must be addressed," Bosma said. "My greatest concern is restoring the confidence of the public in their elected officials."