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). Colocalized with GPR83 in the paraventricular nucleus. Expressed in both T-cell subsets and natural killer cells, while it is undetectable in B cells or CD14(+) monocytes. Expressed in peripheral blood mononuclear cells (PBMC) and Jurkat cells (at protein level). Belongs to the G-protein coupled receptor 1 family.