The epsin N-terminal homology (ENTH) domain is a protein module of ϳ150 amino acids found at the N terminus of a variety of proteins identified in yeast, plants, nematode, frog, and mammals. ENTH domains comprise multiple ␣-helices folded upon each other to form a compact globular structure that has been implicated in interactions with lipids and proteins. In characterizing this evolutionarily conserved domain, we isolated and identified tubulin as an ENTH domain-binding partner. The interaction, which is direct and has a dissociation constant of ϳ1 M, was observed with ENTH domains of proteins present in various species. Tubulin is co-immunoprecipitated from rat brain extracts with the ENTH domain-containing proteins, epsins 1 and 2, and punctate epsin staining is observed along the microtubule cytoskeleton of dissociated cortical neurons. Consistent with a role in microtubule processes, the over-expression of epsin ENTH domain in PC12 cells stimulates neurite outgrowth. These data demonstrate an evolutionarily conserved property of ENTH domains to interact with tubulin and microtubules.The epsin N-terminal homology (ENTH) 1 domain is an evolutionarily conserved globular module of ϳ150 amino acids that occurs at the amino terminus of a variety of proteins (1, 2).Originally noted in the plant protein, Af10 (3), the ENTH domain has subsequently been characterized in epsins (2) and enthoprotin (4) (also termed epsinR (5, 6) or Clint (7)), and in yeast proteins including Ent1p/Ent2p (8, 9) and Ent3p (10). Adaptor protein 180 (AP180), clathrin assembly lymphoid myeloid leukemia protein (CALM), Huntingtin-interacting protein-1 (HIP1) and HIP12, and the yeast proteins yAP180 and Sla2p contain a module that is so similar in structure to the epsin ENTH domain that they were initially denoted ENTHbearing proteins (11-13). However, recent structural studies have refined our understanding such that ENTH-like domains from these proteins have been re-designated ANTH domaincontaining proteins in accordance with their higher structural similarity to AP180 rather than epsin (14). In an effort to simplify the nomenclature applied in this study, we refer to these homologous structures as E/ANTH domains when collectively discussing proteins bearing either domain, but maintain the ENTH or ANTH nomenclature when discussing individual proteins.A common feature among many E/ANTH domain-bearing proteins is that their C termini contain peptide motifs, indicative of a functional role in clathrin-mediated membrane budding including clathrin and clathrin adaptor protein-binding elements (1,15). In addition to their interactions with multiple endocytic components, many of the currently characterized E/ANTH proteins, including epsin, AP180, and HIP1/12, are localized to clathrin-coated pits where they function in clathrin-mediated endocytosis (2, 16 -25). Interestingly, enthoprotin is unique in this group because it is predominantly localized to the trans-Golgi network rather than the plasma membrane, and it appears to regulate clathrin-medi...