21447
When applied to glycophorin A TM domain ( GpA - TM ) using the restraint potentials along the helix - helix distance , however , tight interfacial packing of GpA - TM resulted in insufficient conformational sampling at short helix - helix separation .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
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