G protein-coupled receptor for Big LEN, a 16-amino acid neuropeptide produced from the precursor protein, proSAAS (encoded by PCSK1N). Acts through a G(i)-alpha-mediated pathway in response to Big LEN. Big LEN-GPR171 system plays an important role in regulating feeding and metabolism. Also plays a role in modulating fear and anxiety-like behaviors in the basolateral amygdala. Big LEN-GPR171 modulates the mu-type opioid receptor signaling and antinociception (By similarity). Acts as a negative regulator T cell function (PubMed:34615877). {ECO:0000250|UniProtKB:Q8BG55, ECO:0000269|PubMed:34615877}. This is the function of GPR171 (G protein-coupled receptor 171, Ensembl gene identifier ENSG00000174946).