PHILADELPHIA - At the heart of brain diseases such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease, and Parkinson's disease is protein misfolding, in which distorted proteins are unable to perform their normal functions. At present, there is no known way to reverse protein misfolding.
But James Shorter, Ph.D., associate professor of Biochemistry and Biophysics, at the Perelman School of Medicine, University of Pennsylvania, has found a possible way to unravel misfolded proteins by "reprogramming" Hsp104, a common yeast protein. The work was published this week in Cell.
Hsp104 is a "chaperone" protein, one that assists in the proper formation and functioning of other protein complexes. Although Hsp104 is one of the most common proteins on the planet, it has no analogue in humans or animals.
"We don't understand why animals have lost the gene for Hsp104, but at the same time, we've been wondering: 'Is there a therapeutic opportunity in this?'" asks Shorter. "Can we add it back as a disruptive technology to antagonize the protein misfolding that characterizes some diseases?"
In previous studies, Shorter's lab established that the natural version of Hsp104 is active against neurodegenerative proteins such as alpha-synuclein. "We expressed the wild-type protein in a rat model of Parkinson's disease and observed beneficial phenotypes," explains Shorter. "But the wild-type protein just doesn't work as well as we would like."
In the present study, the team screened large libraries of Hsp104 variants to find versions that could both maintain protein structure and break up misfolded clumps. "Luckily several variants came out of our screen that could suppress the toxicity associated with misfolded and clumped FUS, TDP-43, and alpha-synuclein disease proteins in yeast, while also enhancing proper protein function," he adds.
Shorter's team collaborated with the lab of Guy Caldwell at the University of Alabama to test Hsp104 variants in the worm C. elegans and found marked rescue of alpha-synuclein toxicity, the first time that engineered enzymes have been shown to suppress neurodegeneration in a multicellular animal.
"This is very exciting, as there are no agents that are known to rescue neurodegeneration and at the same time reverse protein misfolding," notes first author Meredith Jackrel, Ph.D., a postdoctoral fellow in the Shorter lab. "Certainly nobody's ever tried to reprogram an existing protein to try to accomplish that task."
Shorter identified Hsp104's coiled-coil middle domain as a major area affecting its ability to function as a chaperone, noting that minor mutations in this domain appear to have wide-ranging potential to unlock the molecule's protein clump-busting capabilities. He suggests that the middle domain of Hsp104 functions much like an electrical capacitor, storing the protein's beneficial possibilities. A seemingly small tweak of the middle-domain structure, as well as other parts of the molecule such as the pore loops, can unleash a surprising therapeutic power.
With that power now demonstrated in the relatively primitive worm species, the team's next step will be to move to a more complex animal model in mice, where the side effects of introducing a foreign protein into an organism might be a concern.
Shorter explains that aside from Hsp104's declumping function, "the other major goal from a bioengineering viewpoint is to make the tweaked Hsp104 specific in what it targets because all the variants we have at the moment seem to work across the board. That's not what you want for a therapeutic, because there might be off-target effects."
He stresses that although his protein reengineering approach is not yet a cure or practical treatment for neurodegenerative disease, it's a major first step toward that ultimate goal and shows that clump busting -- what was previously thought impossible -- is within reach, adding, "We've defined that it is possible to achieve clot-busting activity in a simple model system. The challenge is to move it forward from there."
The research was supported by an American Heart Association Post-Doctoral Fellowship; a National Institutes of Health (NIH) training grant (T32GM071339); an NRSA predoctoral fellowship (F31NS079009); an NIH Director's New Innovator Award (DP2OD002177); other NIH grants (R21NS067354, R21HD074510, R01GM099836); a Muscular Dystrophy Association Research Award (MDA277268), and an Ellison Medical Foundation New Scholar in Aging Award.
Penn Medicine is one of the world's leading academic medical centers, dedicated to the related missions of medical education, biomedical research, and excellence in patient care. Penn Medicine consists of the Raymond and Ruth Perelman School of Medicine at the University of Pennsylvania (founded in 1765 as the nation's first medical school) and the University of Pennsylvania Health System, which together form a $4.3 billion enterprise.
The Perelman School of Medicine has been ranked among the top five medical schools in the United States for the past 16 years, according to U.S. News & World Report's survey of research-oriented medical schools. The School is consistently among the nation's top recipients of funding from the National Institutes of Health, with $398 million awarded in the 2012 fiscal year.
The University of Pennsylvania Health System's patient care facilities include: The Hospital of the University of Pennsylvania -- recognized as one of the nation's top "Honor Roll" hospitals by U.S. News & World Report; Penn Presbyterian Medical Center; Chester County Hospital; Penn Wissahickon Hospice; and Pennsylvania Hospital -- the nation's first hospital, founded in 1751. Additional affiliated inpatient care facilities and services throughout the Philadelphia region include Chestnut Hill Hospital and Good Shepherd Penn Partners, a partnership between Good Shepherd Rehabilitation Network and Penn Medicine.
Penn Medicine is committed to improving lives and health through a variety of community-based programs and activities. In fiscal year 2012, Penn Medicine provided $827 million to benefit our community.
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.