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【bio-news】Scientists solve sour taste proteins
DURHAM, N.C. ?A team led by Duke University Medical Center researchers has discovered two proteins in the taste buds on the surface of the tongue that are responsible for detecting sour tastes.
While the scientific basis of other primary types of flavors, such as bitter and sweet, is known, this is the first study to define how humans perceive sour taste, said team senior scientist Hiroaki Matsunami, Ph.D., an assistant professor of molecular genetics and microbiology.
The identification of these proteins, called PKD1L3 and PKD2L1, could lead to ways to manipulate the perception of taste in order to fool the mouth that something sour, such as some children's medicines or health foods, tastes sweet, he said.
The team's findings appear in the online edition of the Proceedings of the National Academy of Sciences and will be published in the August 15, 2006, issue of the journal. The work was supported by the National Institutes of Health.
Mammals, including humans, can detect five primary flavors: bitter, sweet, salty, sour, and umami (known to the West as the taste of monosodium glutamate or MSG). Each taste bud on the tongue contains separate, distinct subsets of cells that specifically detect each taste -- sweet cells respond to sweet substances, bitter cells to bitter substances, and so on. Taste receptors, proteins on the surface of these cells, are responsible for detecting the "taste" of a particular food or chemical and triggering signals sent to the taste centers of the brain. In their study, the researchers used fluorescent tags to label the subsets of cells that are known to be responsible for bitter, sweet, and umami taste, as well as the subsets of cells that express PKD1L3 and PKD2L1. By "reading" the tags, they found no overlap between the subsets of cells involved in the first three tastes and the cells in which PKD1L3 and PKD2L1 are active. Matsunami said this result suggested that those proteins could be responsible for sensing either sour or salty taste.
In action, the two proteins combine to form "ion channels," porelike proteins in the membranes of taste cells, Matsunami said. These channels in turn control the flow of calcium ions, or electrically charged forms of calcium, in and out of the cells. This flow of ions essentially conditions the cell so that electrical signals can be sent to the brain in response to various stimuli.
The researchers stimulated mammalian cells expressing PDK1L3 and PKD2L1 with various taste chemicals to identify which stimuli caused the ion channels to open. To visualize the presence of calcium ions in the cell, the scientists loaded the cells with two calcium-sensitive fluorescent dyes -- one that glowed green when the calcium concentration was high, the other that glowed red when the concentration was low.
When they added sour-tasting acids to the cells, the ion channels went from closed to open, enabling calcium ions to flow in, increasing their concentration within the cell and changing the cells from red to green, Matsunami said. The channels remained closed when confronted with salt, sweeteners, or bitter solutions. The increased concentration of calcium in the cell may then trigger the signal that the brain eventually perceives as sour taste, he said.
Matsunami said he plans to use this finding to screen for chemicals that can block the function of these sour taste cells. The research also could lead to a better understanding of how the sense of taste functions neurologically, he said. "We still do not know what is happening in the brain -- that is, exactly how the brain would interpret the signals coming from the tongue to tell the difference between lemons and lemonade," Matsunami said. Future experiments using live animals as test models will be needed to answer remaining questions about taste sensation, he said. 认领这个 科学家搞定感酸蛋白
北卡罗莱纳州DURHAM-由Duke大学医学中心研究者领导的小组在舌表面味蕾上发现两个负责感觉酸味的蛋白。
分子遗传学和微生物学助理教授，小组中高级科学家Hiroaki Matsunami博士说，其他味道像苦味和甜味的科学依据都已经弄清了，而这是第一个能够确定人类如何感知酸味的研究。
命名为PKD1L3和PKD2L1的两个蛋白的鉴定为我们能够操控味觉并使嘴误感觉到酸味提供了方法，就像儿童的药物和健康食品吃起来是甜的一样。
这个小组的发现出现在美国科学院院刊的在线版上并将发表于该刊的2006年8月15日期上。此项研究有国立卫生研究所资助。
哺乳动物包括人类能够感知五味：苦，甜，咸，酸和皂（西方认为味精-谷氨酸单钠的味道）。舌头上的每个味蕾都包含独特的感知特定味道的细胞亚群--甜味细胞感知甜味，苦味细胞感知苦味等等。这些细胞表面的蛋白即味觉感受器负责感知特定食物或者化学物质的味道，并将触发信号发送至大脑的味觉中枢。研究者在研究过程中给已知负责感知苦，甜，皂味的细胞亚群和表达PKD1L3，PKD2L1的细胞亚群加荧光标签。通过对标签的识别，他们发现已知负责感知苦，甜，皂味的细胞亚群和表达PKD1L3，PKD2L1的细胞亚群没有重叠。Matsunami说，这种结果说明这两种蛋白要么负责感知酸味，要么负责感知甜味。
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作者:admin@医学,生命科学 2011-02-15 05:11
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