The retromer complex 1,2 is required for the sorting of acid hydrolases to lysosomes 3-7, transcytosis of the polymeric Ig receptor 8, Wnt gradient formation 9,10, iron transporter recycling 11, and processing of the amyloid precursor protein 12. Human retromer consists of two smaller complexes, the cargo recognition Vps26:Vps29:Vps35 heterotrimer, and a membrane-targeting heterodimer or homodimer of SNX1 and/or SNX2 13. The crystal structure of a Vps29:Vps35 subcomplex shows how the metallophosphoesterase-fold subunit Vps29 14,15 acts as a scaffold for the C-terminal half of Vps35. Vps35 forms a horseshoe-shaped right-handed α-helical solenoid whose concave face completely covers the metal-binding site of Vps29 and whose convex face exposes a series of hydrophobic interhelical grooves. Electron microscopy shows that the intact Vps26:Vps29:Vps35 complex is a stick-shaped, somewhat flexible, structure, ∼ 21 nm long. A hybrid structural model derived from crystal structures, electron microscopy, interaction studies, and bioinformatics shows that the α-solenoid fold extends the full length of Vps35, and that Vps26 is bound at the opposite end from Vps29. This extended structure presents multiple binding sites for the SNX complex and receptor cargo, and appears capable of flexing to conform to curved vesicular membranes.The retromer cargo recognition complex consists of the 38-kDa Vps26, 20-kDa Vps29, and 92-kDa Vps35 subunits. The structures of the two smaller subunits have been determined in isolation. Vps26 is a structural cousin of the arrestins 16, a family of trafficking proteins that directly bind to cell surface receptors and direct their internalization. Vps29 has a metallophosphoesterase fold 14,15 that can bind two metal ions. Compared to functional metallophosphoesterases, a key His that serves as a catalytic base in the 6To whom correspondence should be addressed:James H. Hurley, (301) 402−4703, fax (301) 480−0639; E-mail: hurley@helix.nih.gov. 2 These authors contributed equally. Author contributions A. L. R. and A. H. expressed and purified protein complexes, crystallized the Vps29:Vps35 C-terminal subcomplex, collected crystallographic data, and determined and refined the crystal structure; A. H. carried out phosphatase assays; R. R. and N. M. carried out immunoprecipitation and optical microscopy studies; G. E. and A. C. S. carried out and interpreted electron microscopy studies; A. V. K. carried out sequence analysis; and J. H. H., J. S. B., and A. C. S. designed the study. A. H. and A. L. R. contributed equally to this study. Here we take a structural approach to gain insight into the function of retromer. Author informationThe crystal structure of a Vps29:Vps35 subcomplex, containing the C-terminal 40% of the large Vps35 subunit, was determined at 2.8 Å resolution (Fig. 1a, Fig. S1, Table S1). The Cterminal portion of Vps35 consists of a single right-handed superhelix with a pitch of 12 Å and a total of 13 helices (Fig. 1a, S2). Vps35 resembles many other helical solenoid proteins, includ...

Measles is a highly contagious human disease. We used cryo-electron microscopy and single particle-based helical image analysis to determine the structure of the helical nucleocapsid formed by the folded domain of the measles virus nucleoprotein encapsidating an RNA at a resolution of 4.3 angstroms. The resulting pseudoatomic model of the measles virus nucleocapsid offers important insights into the mechanism of the helical polymerization of nucleocapsids of negative-strand RNA viruses, in particular via the exchange subdomains of the nucleoprotein. The structure reveals the mode of the nucleoprotein-RNA interaction and explains why each nucleoprotein of measles virus binds six nucleotides, whereas the respiratory syncytial virus nucleoprotein binds seven. It provides a rational basis for further analysis of measles virus replication and transcription, and reveals potential targets for drug design.