Indication of complex protein (7)
I believe the answer is:
pointer
'indication' is the definition.
(I've seen this before)
'complex protein' is the wordplay.
'complex' is an anagram indicator.
'protein' is an anagram of 'POINTER'.
'of' is the link.
(Other definitions for pointer that I've seen before include "Suggestion" , "Gun dog" , "The dog provides an indication" , "under control of mouse" , "Tip; dog" .)