Neurology Today: November 16, 2017 - Volume 17 - Issue 22 - p 29–31
doi: 10.1097/01.NT.0000527325.89477.81
ARTICLE IN BRIEF
Scientists are hoping to learn more about the structure of the LRRK2 protein, implicated in Parkinson's disease, as it returns from the gravity-free environment of the International Space Station
Thank a children's book for inspiring an experiment involving the launch in August 14 of a key protein linked to the risk of Parkinson's disease on a rocket headed to the International Space Station.
Hundreds of thousands of copies of the protein, leucine-rich repeat kinase 2 (LRRK2), were combined on Earth earlier this summer with a chemical soup designed to precipitate the proteins into crystals. But before crystallization could begin, the preparation was flash-frozen in liquid nitrogen and packed aboard the SpaceX CRS-12 cargo resupply mission.
Two weeks later, on August 25, astronaut Peggy Whitson removed the container from its freezer, allowing the contents to reach room temperature and finally begin crystallizing. In the microgravity environment, researchers hope, the crystals will grow more perfectly than ever achieved on Earth. The goal, with the help of X-ray crystallography, is to finally peer into the nooks and crannies of the protein's internal structure in order to develop drugs that fit most snugly.
“The Michael J. Fox Foundation has put in over a hundred million dollars into research on LRRK2 beginning around 2005,” said Marco Baptista, PhD, a principal investigator of the study and a director of the foundation's research programs. “In all that time, we still haven't figured out the protein's atomic structure. This is something that we simply have to try.”
The experiment, conducted in partnership with the Center for the Advancement of Science in Space (CASIS), is formally titled CASIS PCG 7.
Although hundreds of other protein crystals have been grown in near-Earth orbit over the past two decades, Dr. Baptista said he became aware of the approach only last year, while helping his son, Marc, with a kindergarten homework project.
“He had to write three things he didn't know about the International Space Station,” Dr. Baptista recalled. While perusing an illustration of the ISS in the book Stephen Biesty's Incredible Explosions: Exploded Views of Astonishing Things (DK Children, 1996), he noticed an area nicknamed the “Crystal Garden,” where protein crystals are grown.
“We had tried so many other ways to grow the LRRK2 crystal, but not on ISS,” he said.
So began a project aimed at understanding a protein that has drawn enormous industry from academics and pharmaceutical companies alike as a potential drug target.
IMPORTANCE OF LRRK2
Mutations in the gene coding for LRRK2 were first identified in 2004 as being linked to familial forms of Parkinson's disease in families, with the highest prevalence seen in the Berber peoples of North Africa. Such cases account for an estimated 5 percent of people with Parkinson's, more than for most other mutations associated with the disease. Of additional interest, Dr. Baptista said, the disease manifests in those familial patients in much the same way as in sporadic cases, primarily after age 60.
“There's a lot of converging biology regarding LRRK2,” Dr. Baptista said. “And it's druggable. That's a key concern for the pharmaceutical industry. This is a class of proteins that companies have a lot of experience in drugging, so it really makes it a low-hanging fruit to go after.”
Andrew West, PhD, professor of neurology and co-director of the Center for Neurodegeneration and Experimental Therapeutics at the University of Alabama at Birmingham, has been running a program for five years aimed at identifying LRRK2 inhibitors. The gene coding for LRRK2, he said, is “one of the most important genes underlying Parkinson susceptibility.”
Moreover, Dr. West added, heightened levels of the LRRK2 protein have been identified in sporadic cases. “There is good reason to believe that LRRK2 may be important in Parkinson's disease patients that lack LRRK2 mutations,” he said.
While drugs designed to inhibit its activity have been tested in animal models, he said, “Everything has been trial and error. We don't know how any of the drugs we have that block LRRK2 are binding.”
Because human trials of LRRK2 inhibitors have not yet begun, he said, “This is the right time to make sure that the best of the best inhibitors makes it into patients.” For that, he said, “We really need some structural information to have a more targeted, rational development pipeline.”
Mark R. Cookson, PhD, senior investigator of the Laboratory of Neurogenetics at the National Institute of Aging, said that sending the protein to the ISS in hopes of growing a better crystal is well worth doing. “The people running this experiment are as likely to succeed as anyone,” Dr. Cookson said. “But it's just really hard to know if this is going to be the thing that finally works to grow a good, diffracting crystal.”
PROMISE AND PERIL
Enough attempts have been made to grow proteins in space that statistics on the likelihood of success are known, according to Lawrence J. DeLucas, PhD, the retired astronaut and biochemist who designed the first such experiment for a space shuttle flight in 1985, at a cost of $2,500.
“We found that if you flew a protein one time on a mission, the chance it would come back and give you the best crystal data set ever seen was around 8 percent,” Dr. DeLucas told Neurology Today. “If ycou flew it twice, the chance rose to 28 percent. After three times, your chances were 40 percent. And after ten attempts, the chance that you will get the best data set ever is a hundred percent.”
The reason that growing protein crystals in space works better than on Earth is that gravity causes the lighter molecules of a protein to rise and the heavier parts to fall in solution, creating movement that results in imperfect alignments when the proteins crystallize.
“The only thing that makes the molecules move in the microgravity of space is random diffusion,” Dr. DeLucas explained. “It's much slower, so the crystals form more slowly.”
Even so, space is not a cure-all for coaxing proteins to form perfect crystals, he said.
“If you have a protein that is not homogenous and does not have one stable conformation, so there is a molecular domain of the big protein that is slopping around in and out of different conformations, space won't fix that,” he said.
Sebastian Mathea, PhD, lead scientist in structural biology at the University of Oxford's Target Discovery Institute, was tasked with preparing the LRRK2 sample for its space flight.
“We have been trying to grow these crystals for quite some time now, five years,” Dr. Mathea said. “When we do the experiment here, if it does not work, we try again. For space, it was very important that every single step was performed perfectly. It's quite, quite hyphenate.”
One nice aspect of the experiment is the short time it will take to get results, Dr. Baptista said. “Currently, the best resolution of the LRRK2 protein yet achieved is down to 7.5 angstroms, Dr. Baptista said. “If we get back crystals with a resolution of 6 angstroms or under,” he added, “that would move the dial.”
LINK UP FOR MORE INFORMATION:
Guaitoli G, Raimondi F, Gisbach BK, et al Structural model of the dimeric Parkinson's protein LRRK2 reveals a compact architecture involving distant interdomain contacts http://http://www.pnas.org/content/113/30/E4357.abstract. Proc Natl Acad Sci USA 2016; 113 (30): E4357–66. doi: 10.1073/pnas.1523708113. Epub 2016 Jun 29.
http://journals.lww.com/neurotodayonline/Fulltext/2017/11160/Key_Protein_Linked_to_Parkinson_s_Returns_from.10.aspx?WT.mc_id=HPxADx20100319xMP
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