Nucleic acid molecules encoding full length PTP20, PCP-2, BDP1, mCLK2, mCLK3, mCLK4, and SIRP polypeptides, portions of such nucleic acid molecules, nucleic acid vectors containing such nucleic acid molecules, recombinant cells containing such nucleic acid vectors, polypeptides purified from such recombinant cells, antibodies to such polypeptides, and methods of identifying compounds that bind such polypeptides or abrogate their interactions with natural binding partners. Methods for diagnosing abnormal conditions in an organism with PTP20, PCP-2, BDP1, mCLK2, mCLK3, mCLK4, and SIRP related molecules or compounds. PTP20, PCP-2, BDP1, mCLK2, mCLK3, mCLK4, or SIRP polypeptides, nucleic acids encoding such polypeptides, cells, tissues and animals containing such nucleic acids, antibodies to such polypeptides, assays utilizing such polypeptides, and methods relating to all of the foregoing. Methods for treatment, diagnosis, and screening are provided for diseases related to PTP20, PCP-2, BDP1, mCLK2, mCLK3, mCLK4, and SIRP polypeptide or conditions characterized by an abnormal interaction between such a polypeptide and its binding partner.