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NMR and X - ray results provide strong supporting evidence for a structural model in which phosphorylated serine repeats ( pSX ) 4 complex with divalent cations Ca ( 2 + ) and Mg ( 2 + ) to form rigid nanocrystalline beta - sheet structures in caddisfly silk .
 Chemical: phosphorylated serine; Chemical: Ca ( 2 + ); Chemical: Mg ( 2 + )
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: phosphorylated serine; Chemical: Ca ( 2 + ); Chemical: Mg ( 2 + )