Phosphoglucose isomerase (PGI) contains two SIS (Sugar ISomerase) domains. This classification is based on the alignment of the second SIS domain. PGI is a multifunctional enzyme which as an intracellular dimer catalyzes the reversible isomerization of glucose 6-phosphate to fructose 6-phosphate. As an extracellular protein, PGI also has functions equivalent to neuroleukin (NLK), autocrine motility factor (AMF), and maturation factor (MF). Evidence suggests that PGI, NLK, AMF, and MF are closely related or identical. NLK is a neurotrophic growth factor that promotes regeneration and survival of neurons. The dimeric form of NLK has isomerase function, whereas its monomeric form carries out neurotrophic activity. AMF is a cytokine that stimulates cell migration and metastasis. MF mediates the differentiation of human myeloid leukemic HL-60 cells to terminal monocytic cells.
Jiyao W et al.(2023). "The conserved domain database in 2023.",