Neuron-specific restriction factor that prevents herpes simplex virus 1 (HHV-1) infection in the brain by blocking viral entry (PubMed:39048823, PubMed:39048830). Also able to restrict herpes simplex virus 2 (HHV-2) infection, although to a lesser extent (PubMed:39048823). Acts by preventing the association between the viral glycoprotein D (gD) and its cell surface receptor NECTIN1, thereby inhibiting fusion of the virus and the cell membrane (PubMed:39048823, PubMed:39048830). Also able to prevent the association between the viral glycoprotein B (gB) and MYH9/NMMHC-IIA and MYH10/NMMHC-IIB receptors (PubMed:39048823). May be a tumor suppressor in brain cancers (PubMed:12743596). {ECO:0000269|PubMed:12743596, ECO:0000269|PubMed:39048823, ECO:0000269|PubMed:39048830}. This is the function of Ensembl gene identifier ENSG00000241697 (TMEFF1, transmembrane protein with EGF like and two follistatin like domains 1).