A protein found on brain cells, known to contribute to nicotine addiction, may also be the key to developing drugs for a wide range of diseases and medical conditions, including obesity, schizophrenia, and Alzheimer’s disease.

In a recent study, researchers at Brown University in Providence discovered the protein, called the alpha-7 receptor, has a previously unsuspected wide-ranging influence on processes within the body.

It affects dozens of cellular interactions and interacts with 55 other proteins, including a separate class of receptor that is a target for about 40 percent of all therapeutic drugs.

“These [receptors] as a group are very important because they control a lot of critical functions, like heart rate,’’ said Edward Hawrot, the study’s lead author and a professor of molecular science, molecular pharmacology, physiology, and technology at Brown. “What was surprising was that we saw a connection between [the] proteins, because these two receptor families are very, very different.’’

Alpha-7 receptors have long been known, but their function was something of a mystery until the Brown researchers revealed their importance.

“They’ve learned that these nicotinic receptors have a profound influence on other systems in the body,’’ said J. Donald deBethizy, chief executive of Targacept in Winston-Salem, N.C., which makes drugs that target receptors.

DeBethizy said the Brown research shows “the alpha-7 receptor may be at the apex of many, many important biological responses.’’

The alpha receptor is like a doughnut on the surface of a cell. The “hole,’’ normally closed, opens when it comes into contact with acetylcholine, a neurotransmitter, or a chemical that acts like a trigger for various activities within the cell. Acetylcholine occurs naturally in the body, but its effects can be mimicked by nicotine, which is why alpha-7 and its relatives are called nicotinic receptors.

The Brown research indicated that alpha-7 drugs could provide a way to compensate for the loss of acetylcholine in Alzheimer’s disease and similar afflictions.

“When you don’t have enough acetylcholine released to activate the receptors, people can’t remember and they have cognitive impairment,’’ said Merouane Bencherif, vice president at Targacept. “What we would do is provide a drug that is not metabolized that acts on nicotinic receptors. So essentially, you’re compensating for the deficit that exists in Alzheimer’s disease.’’

DeBethizy said the “alpha-7 target is a very hot area in neuroscience,’’ but approved drugs aimed at the receptor have had an unforeseen downside: They react with another receptor system, causing nausea and gastrointestinal side effects.

Targacept has had some success with drugs targeting other alpha class receptors, including one now in early clinical trials that has shown promise in treating the effects of aging, he said.

The company is also working on an alpha-7 drug for treating cognitive dysfunction in schizophrenics, one of the leading reasons “schizophrenics can’t function better even when they’re being treated with [an] antipsychotic,’’ deBethizy explained.

It’s estimated 90 percent of schizophrenics smoke. That’s because the nicotine has therapeutic effects for schizophrenics that it doesn’t have for others, said Tony George, a professor of psychiatry at the University of Toronto Centre for Addiction and Mental Health.

“For schizophrenics, it will remedy deficits in memory and attention functions,’’ said George. He said a drug that could provide the benefits of nicotine to schizophrenics without tobacco would be beneficial.

“Tobacco addiction is now the leading reason why people with schizophrenia die,’’ he said. “They succumb to tobacco-related illness.’’

© Copyright 2009 Globe Newspaper Company.