Provided is binding protein comprising an antigen binding fragment that specifically binds receptor tyrosine-protein kinase ErbB-2 (ErbB2), polynucleotides encoding the binding protein, vectors comprising the polynucleotides, pharmaceutical composition comprising the binding protein as well as methods of using the binding protein. The binding protein can be used for treating a disease or disorder, in which an ErbB2 activity is detrimental or inhibiting growth of ErbB2 positive cells or tumors synergistically with another ErbB2 antibody such as Trastuzumab. The binding protein can also be used for enhancing internalization of an agent or another ErbB2 antibody, for example. Trastuzumab, into ErbB2 positive cells.
