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action or later. Please see Debugging in WordPress for more information. (This message was added in version 6.7.0.) in /home4/scienrds/scienceandnerds/wp-includes/functions.php on line 6114Source:https:\/\/www.quantamagazine.org\/how-a-human-smell-receptor-works-is-finally-revealed-20230501\/#comments<\/a><\/br> Human olfactory receptors belong to an enormous family of proteins known as G-protein-coupled receptors (GPCRs). Situated within cell membranes, these proteins contribute to a vast array of physiological processes by detecting all kinds of stimuli, from light to hormones.<\/p>\n Over the past two decades, researchers have determined detailed structures for an ever-expanding number of GPCRs \u2014 but not for the olfactory receptors among them. To get enough receptors for these studies, researchers must produce them in cultured cells. However, olfactory receptors generally refuse to mature properly when grown outside olfactory neurons, their natural habitat.<\/p>\n To overcome this problem, Matsunami and Claire de March<\/a>, who was a research associate in Matsunami\u2019s lab, began exploring the possibility of genetically altering olfactory receptors<\/a> to make them more stable and easier to grow in other cells. They joined forces with Aashish Manglik<\/a>, a biochemist at the University of California, San Francisco, and Christian Billesb\u00f8lle<\/a>, a senior scientist in Manglik\u2019s lab.<\/p>\n Although this effort was progressing, the team decided to give the extraction of a natural receptor one more shot. \u201cIt\u2019ll probably fail just like everybody else has,\u201d Manglik recalled thinking. \u201c[But] we should try it anyway.\u201d<\/p>\n They improved their odds by picking an odor receptor, OR51E2, that is also found outside the nose \u2014 in the gut, the kidney, the prostate and other organs. Through Billesb\u00f8lle\u2019s meticulous efforts, they managed to obtain enough OR51E2 to study. They then exposed the receptor to an odor molecule that they knew it detected: propionate, a short fatty acid produced by fermentation.<\/p>\n To generate detailed images of the receptor and propionate locked together, the interaction that triggers a sensory neuron to fire, they used cryo-electron microscopy, an advanced imaging technique that captures snapshots of proteins that have been rapidly frozen.<\/p>\n The team found that within the structure of the interlocked molecules, the OR51E2 had trapped propionate within a small pocket.\u00a0When they enlarged the pocket, the receptor lost much of its sensitivity to propionate and to another small molecule that normally activates it. The tweaked receptor preferred larger odor molecules, which confirmed that the size and chemistry of the binding pocket tunes the receptor to detect only a narrow set of molecules.<\/p>\n The structural analysis also uncovered a small, flexible loop atop the receptor, which locks down like a lid over the pocket once an odor molecule binds inside it. The discovery suggests that this highly variable looping piece may contribute to our ability to detect diverse chemistry, according to Manglik.<\/p>\n OR51E2 may still have other secrets to share. Although the study focused on the pocket that holds propionate, the receptor may possess other binding sites for other odors, or for chemical signals it might encounter in tissues outside the nose, the researchers say.<\/p>\n Also, the microscopy images revealed only a static structure, but these receptors are in fact dynamic, said Nagarajan Vaidehi<\/a>, a computational chemist at the Beckman Research Institute of the City of Hope who also worked on the study.\u00a0Her group used computer simulations to visualize how OR51E2 probably moves when it\u2019s not frozen.<\/p>\n For de March, who has moved to France\u2019s National Center for Scientific Research, the map of OR51E2 turned years of speculation into reality.\u00a0She noted that she has been studying theoretical models of odorant receptors throughout her career: The new findings were \u201cthe first time I had the answers to everything I was wondering when I was working on these theoretical models,\u201d she said.<\/p>\n Other human olfactory receptors, especially those closely related to OR51E2, likely function similarly, Matsunami said. He and other researchers see the identification of the functional structure as a step toward understanding the underlying logic that guides the operation of our sense of smell.<\/p>\n But they have a long way to go. Scientists have at best an inkling of which molecules activate only about a quarter of the human olfactory receptors.<\/p>\n Still, with more structures like that of OR51E2, it may be possible to open the biological black box of olfaction, said Joel Mainland<\/a>, an olfactory neuroscientist at the Monell Chemical Senses Center who was not involved in the new research.\u00a0With more insights into how the neural coding for olfaction works, \u201cthe hope is that now we\u2019ll be able to make confident models<\/a> about what odors will bind to given receptors,\u201d he said.<\/p>\n The question of how receptors selectively respond to airborne chemicals is only a piece of the bigger puzzle of smell, however. To fully understand the sense, researchers also need to figure out how the brain translates the incoming information about receptor activity into a perception, said Matt Wachowiak<\/a>, an olfactory neuroscientist at the University of Utah who was not involved in the study.<\/p>\n In the real world, almost everything we smell contains a mix of many chemicals, at varying concentrations. \u201cSomehow we recognize that pattern, generally very quickly, and in different situations,\u201d he said. \u201cThe real challenge is figuring out: How does the brain do that?\u201d<\/p>\n<\/div>\n <\/br><\/br><\/br><\/p>\n
\nHow a Human Smell Receptor Works Is Finally Revealed<\/br>
\n2023-05-03 21:59:12<\/br><\/p>\nThe Underlying Logic of Scent<\/h2>\n