@article {18697,
	title = {Crystal Structure and Solution NMR Studies of Lys48-linked Tetraubiquitin at Neutral pH},
	journal = {Journal of Molecular Biology},
	volume = {367},
	year = {2007},
	month = {2007/03/16/},
	pages = {204 - 211},
	abstract = {Ubiquitin modification of proteins is used as a signal in many cellular processes. Lysine side-chains can be modified by a single ubiquitin or by a polyubiquitin chain, which is defined by an isopeptide bond between the C terminus of one ubiquitin and a specific lysine in a neighboring ubiquitin. Polyubiquitin conformations that result from different lysine linkages presumably differentiate their roles and ability to bind specific targets and enzymes. However, conflicting results have been obtained regarding the precise conformation of Lys48-linked tetraubiquitin. We report the crystal structure of Lys48-linked tetraubiquitin at near-neutral pH. The two tetraubiquitin complexes in the asymmetric unit show the complete connectivity of the chain and the molecular details of the interactions. This tetraubiquitin conformation is consistent with our NMR data as well as with previous studies of diubiquitin and tetraubiquitin in solution at neutral pH. The structure provides a basis for understanding Lys48-linked polyubiquitin recognition under physiological conditions.},
	keywords = {crystal structure, Lys48-linked, polyubiquitin chains, tetraubiquitin, ubiquitin},
	isbn = {0022-2836},
	doi = {10.1016/j.jmb.2006.12.065},
	url = {http://www.sciencedirect.com/science/article/pii/S0022283606017554},
	author = {Eddins,Michael J. and Varadan,Ranjani and Fushman, David and Pickart,Cecile M. and Wolberger,Cynthia}
}
@article {18719,
	title = {Structural Properties of Polyubiquitin Chains in Solution},
	journal = {Journal of Molecular Biology},
	volume = {324},
	year = {2002},
	month = {2002/12/06/},
	pages = {637 - 647},
	abstract = {Because polyubiquitin chain structure modulates Ub-mediated signaling, knowledge of the physiological conformations of chain signals should provide insights into specific recognition. Here, we characterized the solution conformations of K48-linked Ub2 and Ub4 using a combination of NMR techniques, including chemical shift mapping of the interdomain interface, domain orientation measurements on the basis of 15N relaxation and residual dipolar couplings, and the solvent accessibility studies. Our data indicate a switch in the conformation of Ub2, from open to closed, with increasing pH. The closed conformation features a well-defined interface that is related to, but distinguishable from, that observed in the Ub2 crystal structure. This interface is dynamic in solution, such that important hydrophobic residues (L8, I44, V70) that are sequestered at the interface in the closed conformation may be accessible for direct interactions with recognition factors. Our results suggest that the distal two units of Ub4, which is the minimum signal for efficient proteasomal degradation, may adopt the closed Ub2 conformation.},
	keywords = {chemical shift mapping, domain orientation measurements, polyubiquitin chains, spin relaxation, ubiquitin},
	isbn = {0022-2836},
	doi = {10.1016/S0022-2836(02)01198-1},
	url = {http://www.sciencedirect.com/science/article/pii/S0022283602011981},
	author = {Varadan,Ranjani and Walker,Olivier and Pickart,Cecile and Fushman, David}
}
