Provided herein are antigen binding polypeptides and complexes thereof having agonist activity. Also provided are methods for screening for complexes or polypeptides having agonist activity, enhancing the agonist activity of a polypeptide, and for agonizing a cell surface receptor using the complexes and polypeptide described herein.本文提供具有促效劑活性之抗原結合多肽及其複合物。亦提供篩選具有促效劑活性之複合物或多肽、增強多肽之促效劑活性及使用本文中描述之複合物及多肽促效細胞表面受體之方法。