Research Report 2010 - MDC

Figure 2. Crystal structure of the human golgin p115. The globular head region of p115, p115 GHR , is composed of nine canonical armadillo repeats(ARM1 to ARM9) and an unsual repeat, ARM10, whose additional α-helix (USO) folds into the concave surface of p115 (left). In the crystal, p115 GHRis in a dimeric arrangement with C-termini in close vicinity (center). A model of intact p115 containing the coiled-coil and acidic C-terminalregions (right) closely resembles electron micrographs of human p115 and the homologous yeast Uso1p.The crystal structure of KorA bound to an 18-basepairDNA fragment containing a consensus O A site revealeda classical binding mode in which sidechains from therecognition helix of the KorA helix-turn-helix motifmake specific hydrogen-bonded contacts to basepairsin the DNA major groove. The dimer iza tion domain of ofKorA has a sequence that is conserved in the homolo -gous RP4-encoded proteins TrbA and KlcB. Based on thecrystal structures of DNA-bound KorA and KorB we proposea model for repressor co-operation in RP4 generegulation in which a contact between the flexible N-terminus of KorB with the conserved dimerizationdomain of KorA or TrbA is postulated (Figure 1).According to this model, the flexibility of KorB serves tomeasure the distance between operators along theDNA while allowing for different spatial dispositions ofthe contact sites on KorA or TrbA caused by the doublehelixtwist.Vesicular transport to the Golgi apparatusVesicular transport in eukaryotic cells depends on conservedsets of proteins involved in the sequential stepsof vesicle budding, uncoating, and tethering to the targetmembrane, as well as in membrane fusion andcargo release. Tethering, the process in which a firstphysical contact between vesicle and target membraneis established, is regulated by a small GTPase belongingto the Rab/Ypt family and involves both heteromultimerictethering complexes and factors characterized byextended coiled-coil regions. Vesicle tethering to theGolgi apparatus of human cells thus involves the Rab1GTPase, the transport protein particle (TRAPP) consistingof at least seven different subunits and p115 or othercoiled-coil containing proteins of the golgin family. Weare taking a combined biochemical and structuralapproach to studying the role of these molecules in110 Cancer Research