O-glycosylation
The Chemistry Clicked: Two NIH-Supported Researchers Win 2022 Nobel Prize in Chemistry
Posted on by Lawrence Tabak, D.D.S., Ph.D.
Through the years, NIH has supported a total of 169 researchers who have received or shared 101 Nobel Prizes. That’s quite a testament to the world-leading science that NIH pursues and its continued impact on improving human health and well-being.
Those numbers include the news late last week that the 2022 Nobel Prize in Chemistry was shared by two long-time grantees for their work on a transformative scientific approach known as “click chemistry.” This form of chemistry has made it possible for researchers to snap together, like LEGO pieces, molecular building blocks to form hybrid biomolecules, often with easy-to-track imaging agents attached. Not only has click chemistry expanded our ability to explore the molecular underpinnings of a wide range of biological processes, but it has provided us with new tools for developing drugs, diagnostics, and a wide array of “smart” materials.
For K. Barry Sharpless, Scripps Research, La Jolla, CA, October 5, 2022 marked the second time that he’s received an early-morning congratulatory call from The Royal Swedish Academy of Sciences. The first such call came in 2001, when Sharpless got the news that he was a co-winner of the Nobel Prize in Chemistry for his discovery of asymmetric catalytic reactions.
This time around, Sharpless was recognized for his groundbreaking studies in the mid-1990s with click chemistry, a term that he coined himself. His initial work established click chemistry as a fast-and-reliable way to attach molecules of interest in the lab [1]. He and co-recipient Morten Meldal, University of Copenhagen, Denmark, who is not funded by NIH, then independently introduced a copper-catalyzed click that further refined the chemistry and helped popularize it across biology and the material sciences [2,3].
For Carolyn R. Bertozzi of Stanford University, Palo Alto, CA, it is her first Nobel. Bertozzi was recognized for expanding the use of click chemistry with so-called bioorthogonal chemistry, which is a copper-free version of the approach that can be used inside living cells without the risk of metal-associated toxicities [4,5].
Bertozzi’s work has been especially interesting to me because of her focus on glycans, which I’ve studied throughout my career. Glycans are the carbohydrate molecules that coat the surfaces of our cells and most secreted proteins. They are essential to life, and, in higher organisms, play fundamental roles in basic processes such as metabolism, immunity, and cellular communication.
Glycans also remain poorly understood, largely because, until recently, they have been so difficult for basic scientists to study with traditional techniques. That has changed with development of new tools to study glycans and the enzymes that assemble them. My long-time collaborator, Kelly Ten Hagen, a senior investigator at NIH’s National Institute of Dental and Craniofacial Research, and I collaborated with Carolyn on identifying small molecules that inhibit the enzyme responsible for the first step in mucin-type O-glycosylation [6]
In the early 2000s, Bertozzi and her team introduced bioorthogonal chemistry, which enabled researchers to label glycans and visualize them in a range of cells and living organisms. Her team’s pioneering approach quickly became an essential tool in basic science labs around the world that study glycans, leading to a number of stunning discoveries that would have otherwise been difficult or impossible.
For clinical researchers, click chemistry has emerged as a workhorse in drug discovery and the improved targeting of cancer chemotherapies and other small-molecule drugs. The approach also is being used to improve delivery of antibody-based therapies and to create new biomaterials. Meanwhile, in the material sciences, click chemistry has been used to solve a number of problems in working with polymers and to expand their industrial uses.
Click chemistry is an excellent example of how advances in basic science can build the foundation for a wide range of practical applications, including those aimed at improving human health. It also highlights the value of strong, sustained public funding for fundamental research, and NIH is proud to have supported Sharpless continuously since 1975 and Bertozzi since 1999. I send my sincere congratulations to both of these most-deserving scientists.
References:
[1] Click Chemistry: Diverse chemical function from a few good reactions. Kolb, HC, Finn, MG, Sharpless, KB. Angew. Chem. Int. Ed. 2001, 40 (11), 2004–2021
[2] A stepwise huisgen cycloaddition process: Copper(I)-catalyzed regioselective “Llgation” of azides and terminal alkynes. Rostovtsev VV, Green LG, Fokin VV, Sharpless KB. Angew. Chem. Int. Ed. 2002, 41 (14), 2596–2599.
[3] Peptidotriazoles on solid phase: [1,2,3]-Triazoles by regiospecific copper(I)-catalyzed 1,3-dipolar cycloadditions of terminal alkynes to azides. Tornøe CW, Sengeløv H, Meldal M. J. Org. Chem. 2002, 67 (9), 3057–3064.
[4] A strain-promoted [3 + 2] azide−alkyne cycloaddition for covalent modification of biomolecules in living systems. Agard NJ, Prescher JA, Bertozzi CR. J. Am. Chem. Soc. 2004, 126 (46), 15046–15047
[5] In vivo imaging of membrane associated glycans in developing zebrafish. Laughlin ST, Baskin JM, Amacher SL, Bertozzi CR. Science 2008, 320 (5876), 664–667.
[6] Small molecule inhibitors of mucin-type O-glycosylation from a uridine-based library. Hang, HC, Yu, C, Ten Hagen, KG, Tian, E, Winans, KA, Tabak, LA, Bertozzi, Chem Biol. 2004 Jul;11(7):1009-1016.
Links:
The Nobel Prize in Chemistry 2022 (The Royal Swedish Academy of Sciences, Stockholm)
Video: Announcement of the 2022 Nobel Prize in Chemistry (YouTube)
Click Chemistry and Bioorthogonal Chemistry (The Royal Swedish Academy of Sciences)
Sharpless Lab (Scripps Research, La Jolla, CA)
Bertozzi Group (Stanford University, Palo Alto, CA)
NIH Support:
K. Barry Sharpless: National Institute of General Medical Sciences
Carolyn R. Bertozzi: National Cancer Institute; National Institute of Allergy and Infectious Diseases; National Institute of General Medical Sciences
How One Change to The Coronavirus Spike Influences Infectivity
Posted on by Lawrence Tabak, D.D.S., Ph.D.
Since joining NIH, I’ve held a number of different leadership positions. But there is one position that thankfully has remained constant for me: lab chief. I run my own research laboratory at NIH’s National Institute of Dental and Craniofacial Research (NIDCR).
My lab studies a biochemical process called O-glycosylation. It’s fundamental to life and fascinating to study. Our cells are often adorned with a variety of carbohydrate sugars. O-glycosylation refers to the biochemical process through which these sugar molecules, either found at the cell surface or secreted, get added to proteins. The presence or absence of these sugars on certain proteins plays fundamental roles in normal tissue development and first-line human immunity. It also is associated with various diseases, including cancer.
Our lab recently joined a team of NIH scientists led by my NIDCR colleague Kelly Ten Hagen to demonstrate how O-glycosylation can influence SARS-CoV-2, the coronavirus that causes COVID-19, and its ability to fuse to cells, which is a key step in infecting them. In fact, our data, published in the journal Proceedings of the National Academy of Sciences, indicate that some variants, seem to have mutated to exploit the process to their advantage [1].
The work builds on the virus’s reliance on the spike proteins that crown its outer surface to attach to human cells. Once there, the spike protein must be activated to fuse and launch an infection. That happens when enzymes produced by our own cells make a series of cuts, or cleavages, to the spike protein.
The first cut comes from an enzyme called furin. We and others had earlier evidence that O-glycosylation can affect the way furin makes those cuts. That got us thinking: Could O-glycosylation influence the interaction between furin and the spike protein? The furin cleavage area of the viral spike was indeed adorned with sugars, and their presence or absence might influence spike activation by furin.
We also noticed the Alpha and Delta variants carry a mutation that removes the amino acid proline in a specific spot. That was intriguing because we knew from earlier work that enzymes called GALNTs, which are responsible for adding bulky sugar molecules to proteins, prefer prolines near O-glycosylation sites.
It also suggested that loss of proline in the new variants could mean decreased O-glycosylation, which might then influence the degree of furin cleavage and SARS-CoV-2’s ability to enter cells. I should note that the recent Omicron variant was not examined in the current study.
After detailed studies in fruit fly and mammalian cells, we demonstrated in the original SARS-CoV-2 virus that O-glycosylation of the spike protein decreases furin cleavage. Further experiments then showed that the GALNT1 enzyme adds sugars to the spike protein and this addition limits the ability of furin to make the needed cuts and activate the spike protein.
Importantly, the spike protein change found in the Alpha and Delta variants lowers GALNT1 activity, making it easier for furin to start its activating cuts. It suggests that glycosylation of the viral spike by GALNT1 may limit infection with the original virus, and that the Alpha and Delta variant mutation at least partially overcomes this effect, to potentially make the virus more infectious.
Building on these studies, our teams looked for evidence of GALNT1 in the respiratory tracts of healthy human volunteers. We found that the enzyme is indeed abundantly expressed in those cells. Interestingly, those same cells also express the ACE2 receptor, which SARS-CoV-2 depends on to infect human cells.
It’s also worth noting here that the Omicron variant carries the very same spike mutation that we studied in Alpha and Delta. Omicron also has another nearby change that might further alter O-glycosylation and cleavage of the spike protein by furin. The Ten Hagen lab is looking into these leads to learn how this region in Omicron affects spike glycosylation and, ultimately, the ability of this devastating virus to infect human cells and spread.
Reference:
[1] Furin cleavage of the SARS-CoV-2 spike is modulated by O-glycosylation. Zhang L, Mann M, Syed Z, Reynolds HM, Tian E, Samara NL, Zeldin DC, Tabak LA, Ten Hagen KG. PNAS. 2021 Nov 23;118(47).
Links:
COVID-19 Research (NIH)
Kelly Ten Hagen (National Institute of Dental and Craniofacial Research/NIH)
Lawrence Tabak (NIDCR)
NIH Support: National Institute of Dental and Craniofacial Research
