The present invention relates to protein conjugates comprising an aprotinin-derived polypeptide, which facilitates transport of the conjugate across the blood-brain barrier, and an antibody moiety that selectively binds a target within the CNS. The protein conjugates are further defined by the inclusion of a linker； by the number of polypeptides conjugated to each antibody moiety； by the positions at which the antibody moiety and the polypeptides are conjugated； and by the larger configuration of the conjugate (in which every polypeptide is linked only to the antibody moiety). Modified aprotinin-derived polypeptides, linker-bound antibody moieties, pharmaceutical compositions, kits, and methods of making and using the protein conjugates are also features of the invention.
