Artificial proteins in cerebellum's covering (9)
I believe the answer is:
insincere
'artificial' is the definition.
(thesaurus)
'proteins in cerebellum's covering' is the wordplay.
'covering' indicates the answer is hidden within the clue.
'INSINCERE' is hidden in the letters of 'proteins in cerebellum'.
(Other definitions for insincere that I've seen before include "Not expressing genuine feelings" , "Not genuine, hypocritical" , "False, hypocritical" , "displaying hypocrisy" , "may be laying it on" .)