Macrocyclic and linear peptides promote LAR dimerization and neurite outgrowth

Leucocyte common antigen-related protein (LAR), a member of the type IIa receptor protein tyrosine phosphatase subfamily, regulates biological processes such as cell differentiation, migration, axon elongation, and axon regeneration through its phosphatase activity or cell-cell interactions. The phosphatase activity of LAR is negatively regulated by its dimerization driven by the interaction with extracellular or cytoplasmic molecules. In the nervous system, monomeric LAR suppresses axon elongation and regeneration, while dimeric or oligomeric LAR exhibits the opposite effects. However, intracellular signaling mechanisms associated with LAR dimerization remain incompletely understood due to the lack of tools to control LAR dimerization at will. In this study, we performed peptide library screening using the random nonstandard peptides integrated discovery system, which combines mRNA display with genetic code reprogramming. Through this approach, we identified high-affinity LAR-binding macrocyclic and linear peptides, named L6 and D1L, respectively. These peptides promoted the dimerization of both mouse and human LAR with minimal off-target effects in a split luciferase assay. When L6 or D1L was dimerized using a cross-linker, both peptides showed enhanced LAR dimerization activity, with D1L-derived dimers exhibiting the strongest effect. Furthermore, both monomeric and dimeric peptides promoted neurite outgrowth in cultured hippocampal neurons. Our results identify the de novo peptides as selective modulators of LAR dimerization, providing new tools to probe LAR-mediated signaling in axon growth and regeneration.