You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Protein", "Chemical"].

Please return the output as a JSON object of the format: {"Chemical" : ["Dexamethasone", ...], "Protein" : ["BRCA-1", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Crystal structure of prostate-specific membrane antigen, a tumor marker and peptidase.
Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer cells and nonprostatic solid tumor neovasculature and is a target for anticancer imaging and therapeutic agents. PSMA acts as a glutamate carboxypeptidase (GCPII) on small molecule substrates, including folate, the anticancer drug methotrexate, and the neuropeptide N-acetyl-l-aspartyl-l-glutamate. Here we present the 3.5-A crystal structure of the PSMA ectodomain, which reveals a homodimer with structural similarity to transferrin receptor, a receptor for iron-loaded transferrin that lacks protease activity. Unlike transferrin receptor, the protease domain of PSMA contains a binuclear zinc site, catalytic residues, and a proposed substrate-binding arginine patch. Elucidation of the PSMA structure combined with docking studies and a proposed catalytic mechanism provides insight into the recognition of inhibitors and the natural substrate N-acetyl-l-aspartyl-l-glutamate. The PSMA structure will facilitate development of chemotherapeutics, cancer-imaging agents, and agents for treatment of neurological disorders.
{"Chemical": ["zinc", "methotrexate", "iron", "glutamate", "arginine", "N-acetyl-l-aspartyl-l-glutamate", "folate"], "Protein": ["protease", "glutamate carboxypeptidase", "protease domain", "PSMA ectodomain", "Prostate-specific membrane antigen", "GCPII", "prostate-specific membrane antigen", "PSMA", "peptidase", "transferrin receptor", "transferrin"]}