Production and purification of functional truncated soluble forms of human recombinant L1 cell adhesion glycoprotein from Spodoptera frugiperda Sf9 cells

L1 is a human cell adhesion glycoprotein involved in the development of the central nervous system that comprises six immunoglobulin-like domains (Ig1-Ig6), five fibronectin-type III (FN1-FN5) domains, a single transmembrane region and a cytoplasmic domain. It contains 20 potential N-glycosylation sites and is heavily glycosylated in a variety of cell types. In this work, seven truncated soluble forms including L1 ectodomain (L1/ECD) and Ig domains 5-6 (L1/Ig5-6) have been constructed by PCR and have been cloned, as well as the full-length form (L1), in the stable expression vector for insect cells pMIB/V5-His-TOPO. Spodoptera frugiperda Sf9 cell lines expressing the truncated forms have been obtained, and all proteins were successfully secreted. L1/ECD and L1/Ig5-6 were produced in shake flasks with productions of 3 and 32 mg/L on the third and fourth day of culture, respectively. When L1/Ig5-6 was produced for four days in 2L bioreactor 200 mg/L protein were recovered from the supernatants on the fourth day of culture. Affinity-purified L1/ECD and L1/Ig5-6 were immobilized on poly-d-lysine coated coverslips, and were shown to be active in inducing neurite outgrowth from human NT2N neurons. Therefore, correctly folded and functional truncated forms of human L1 have been produced in high amounts from insect cells using a stable expression system.