Regulates voltage-gated potassium channels assembled from KCNA1, KCNA4 and KCNAB1. It slows down channel inactivation by precluding channel closure mediated by the KCNAB1 subunit. Ligand for ADAM22 that positively regulates synaptic transmission mediated by AMPA-type glutamate receptors (By similarity). Plays a role in suppressing the production of MMP1/3 through the phosphatidylinositol 3-kinase/ERK pathway (PubMed:15047712). {ECO:0000250, ECO:0000269|PubMed:15047712}. This is the function of LGI1 (leucine rich glioma inactivated 1, ENSG00000108231).