CG4520 has been placed in a separate gene group as it is unclear whether this is a functional component of translocase of the outer membrane (TOM) complexes. It displays testis-specific expression and has homology with Tom40 and the testis specific Tom40 subunit tomboy40. However, Tom40 and tomboy40, which have both been shown to be components of TOM complexes, share 68% identity/80% similarity, whilst CG4520 shares less than 25% identity/45% similarity with Tom40/tomboy40. AlphaFold predicts a beta barrel structure.