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Whereas GPCRs used to be viewed as having either " on " or " off " conformational states , it is now recognized that their structures may be finely tuned by ligands and other interacting proteins , leading to the selective activation of specific signaling pathways .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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