Science Concentrates IMAGING
Taking superresolution to the next level New method combines the strengths of earlier imaging techniques
from the beam’s zero-intensity center. By scanning the doughnut in a defined pattern over the sample, the researchers Existing superresolution fluorescence Hell of the Max Planck Institute for Biocan determine the precise position of a microscopy methods such as STED and physical Chemistry, who won the 2014 molecule from how its fluorescence emisPALM have trouble imaging molecules with Nobel Prize in Chemistry for STED. On the sion changes. spatial resolution better than 20 to 40 nm. other hand, “the strength of PALM is that “Because we can relate the position of A new superresolution method called MIN- you’re working with individual molecules.” the molecule to the ‘zero’ of the doughnut, FLUX combines aspects of those earlier But those molecules must emit many thoumany fewer photons are required to find methods to resolve molecules just 6 nm sands of photons in order for scientists to out the position of the molecule than in apart with nanometer precision. (Science get enough fluorescence intensity to deterPALM,” Hell says. 2016, DOI: 10.1126/science.aak9913). mine their positions precisely. The team constructed two arrays of fluSTED and PALM orescent molecules at (and the related techdefined distances from nique STORM) distinone another: 11 nm in guish densely packed one array and 6 nm in features by allowing the other. MINFLUX isolated molecules to determined the molefluoresce while those cules’ positions with a around them remain precision of 2.1 nm and dark. The methods 1.2 nm, respectively. differ in how they deIn addition to imtermine the position proved spatial resoof that fluorescence. An array of fluorescent molecules (left) can be better resolved by MINFLUX lution, the MINFLUX In STED, a laser beam (center) than by PALM/STORM (right). measurements are fast focused into a doughnut enough and require shape turns off fluorescence beneath the In the new method, Hell, Francisco such low laser intensity that the researchbeam but not at the doughnut’s center. In Balzarotti, also at the Max Planck Institute ers used the method for tracking individual PALM, fluorescent molecules are randomly for Biophysical Chemistry, and coworkers molecules in live cells at multiple time switched on and off repeatedly so that only use a doughnut-shaped laser beam for scales. a few well-separated ones are activated at exciting fluorescence instead of turning “It’s a big deal that this method can be a time. The position of the activated moleit off. Because there’s no light intensity used for imaging but also for tracking at cules is determined with a camera. in the doughnut hole, a molecule located short and long time scales,” says Christy “The strength of STED is that the dough- entirely within the hole won’t fluoresce. F. Landes, a superresolution expert at Rice nut always determines where the molecules But a molecule that’s even slightly offset University. “Not all methods are useful for are on and off and hence where the signal from the hole does fluoresce. How much these three very different imaging applicacomes from,” says team leader Stefan W. it fluoresces depends on how far it is tions.”—CELIA ARNAUD
BIOCHEMISTRY
People often turn to a plant-rich diet when they want to reduce their cholesterol intake. But plants often make the complicated sterol too, albeit at a level that’s at least two orders of magnitude less than that made by animals: Cholesterol can be found in leaf lipids, can be used to make a precursor for vitamin D-3, and can be turned into herbivore-deterrents and pathogen poisons, such as α-solanine in potatoes and α-tomatine in tomatoes. Now, more than two centuries after French chemists first discovered cholesterol
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C&EN | CEN.ACS.ORG | JANUARY 2, 2017
in human gallstones, scientists have figured out how plants make the useful molecule. A team of scientists led by Asaph Aharoni at the Weizmann Institute of Science identified the 12 enzymes and 10 chemical conversions used by the tomato plant to convert 2,3-oxidosqualene to cholesterol (Nat. Plants 2016, DOI: 10.1038/nplants.2016.205). They found that the biosynthetic pathway for cholesterol overlaps with the metabolic pathway for phytosterols, the more common and abundant variety of sterols in plants. For example, both pathways share four enzymes,
and both use the same precursor. Aharoni’s team proposes that the cholesterol biosynthetic pathway likely evolved from the phytosterols metabolic route. The discovery of the cholesterol pathway could find use in synthetic biology applications. The work, for instance, “could be a first step toward plant-based engineering of interesting cholesterol derivatives,” writes Thomas J. Bach at the University of Strasbourg, in a commentary associated with the new study (Nat. Plants 2016, DOI: 10.1038/ nplants.2016.213). —SARAH EVERTS
CREDIT: SCIENCE
How tomatoes make cholesterol
