Protect queen in turn out (6)
I believe the answer is:
ensure
'protect' is the definition.
(I've seen this before)
'queen in turn out' is the wordplay.
'queen' becomes 'r' (r is abbreviation regina. e.g. in ER ).
'in' indicates putting letters inside.
'turn out' becomes 'ensue' (ensuing is a kind of turning out).
'r' going inside 'ensue' is 'ENSURE'.
(Other definitions for ensure that I've seen before include "Make certain, secure" , "Make certain for the future" , "Make certain or safe" , "Make certain, confirm" , "Make certain, clinch" .)