The biological function of a fragment of the neurotrophic factor from pigment epithelium: Structural and functional homology with the differentiationfactor of the HL-60 cell line

It was shown that the full-size neurotrophic factor from pigment epithelium (PEDF) induces the cell differentiation of the human promyelocyte leukemia cell line HL-60. A structural analysis of PEDF revealed in its C-terminal region a six-membered peptide fragment PEDF-(352-357) (PEDF-6) whose sequen ce is highly homologous to the 41-46 fragment of the active site of the hum an leukocyte differentiation factor HLDF (HLDF-6). The biological effect of PEDF and synthetic peptides PEDF-6 and HLDF-6 on the HL-60 cells and the e arly gastrula ectoderm of Xenopus laevis embryos was studied. On the basis of the structural and functional homologies of HLDF, PEDF, and their homolo gous peptides and the computer models of the spatial structures of the full -size PEDF and the PEDF with the C-terminal fragment split off thy the clea vage of the Leu(380)-Thr(381) bond in the serpin loop, a hypothesis on the functional role of the serpin loop in PEDF was put forward.