A perspective on transport of proteins into mitochondria: a myriad of open questions.

Mitochondria are the central hub of key cellular processes such as energy conversion, cell signaling, cell cycle regulation and cell differentiation. Therefore, in particular, mitochondrial biogenesis and protein translocation have been the focus of intense research for now nearly half a century. In spite of remarkable progress the field has made, many of the proposed mechanisms remain controversial and none of the translocation pathways is yet understood at the high-resolution level. In this context, the present article is intended to identify and discuss current major open questions and unresolved issues in the field in hope that it will stimulate and engage the pursuit of current efforts and expose new directions.