The three-dimensional crystal structure of the bacteriophage φ29 connector has been solved and refined to 2.1 Å resolution. This 422 kDa oligomeric protein connects the head of the phage to its tail and translocates the DNA into the prohead during packaging. Each monomer has an elongated shape and is composed of a central, mainly α-helical domain that includes a three-helix bundle, a distal α/β domain and a proximal six-stranded SH3-like domain. The protomers assemble into a 12-mer, propeller-like, super-structure with a 35 Å wide central channel. The surface of the channel is mainly electronegative, but it includes two lysine rings 20 Å apart. On the external surface of the particle a hydrophobic belt extends to the concave area below the SH3-like domain, which forms a crown that retains the particle in the head. The lipophilic belt contacts the non-matching symmetry vertex of the capsid and forms a bearing for the connector rotation. The structure suggests a translocation mechanism in which the longitudinal displacement of the DNA along its axis is coupled to connector spinning. © 2002 Academic Press.

This study was supported by grants from the Ministerio de Educación y Cultura of Spain (PB98-1631 and 2FD97-0518 to M.C., PB97-1225-C02 to J.M.V., and PB96-0818 to J.L.C.) and the Generalitat de Catalunya (1999SGR-188 and Centre de Referència en Biotecnologia) to M.C. Synchrotron data collection was supported by the EU grants ERBFMGECT980134 and HPRI-CT-1999-00017 to the EMBL-DESY and by the ESRF. J.P. acknowledges a fellowship from the Ministerio de Educación y Cultura

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