The present invention relates to multi-functional proteins which comprise (i) a signal peptide, (ii) a target specific recognition domain, (iii) a linker region, connecting domain (ii) and domain (iv) which comprises a specific modified hinge region of the human CD8 alpha-chain, and (iv) an effector domain. The present invention furthermore relates to nucleic acids encoding the proteins, expression constructs for expressing the protein in a host cell and host cells. The proteins of the invention are chimeric antigen receptors with an optimized linker or hinge region that are suitable for generating target-specific effector cells, for use as a medicament, in particular in the treatment of cancer and in adoptive, target-cell specific immunotherapy.