An indication of complex protein (7)
I believe the answer is:
pointer
'an indication' is the definition.
(I've seen this before)
'complex protein' is the wordplay.
'complex' indicates an anagram.
'protein' anagrammed gives 'POINTER'.
'of' acts as a link.
(Other definitions for pointer that I've seen before include "Hint (for a dog?)" , "Tip; dog" , "Suggestion" , "Arrow" , "Dog < or horse or" .)