title_body: Structure only conlang? Nouns?
upvoted_answer: It happens with sign languages - often there are two "versions" of a sign language, the first one (less official, natural) is generally used by the community and has its own grammar, the second one (more official, heavily constructed) parallels grammar (syntax) of the corresponding spoken language.
  
  E.g.there is the natural Polish Sign Language, and a rather artificial constructed Signed Polish, following closely the syntax of spoken Polish, so somewhat the opposite of the question, a natural language imposing its grammar over the conlang. But it could be said that the signing system (obviously) imposes its own "phonology" over the spoken language.