Solution structure of At3g28950 from Arabidopsis thaliana.

We determined the solution structure of At3g28950 from A. thaliana, a homolog of At5g39720, whose structure we solved earlier. The secondary structure of the 165-aa protein consists of a 5-strand antiparallel beta-barrel domain flanked by two alpha-helices and a 2-strand beta-sheet; an additional free C-terminal alpha-helix extends into solution. Bioinformatic searches and analyses suggest that members of this growing set of structurally related proteins have been recruited to serve a wide variety of functions ranging from gamma-glutamyl cyclotransferase activity to participation in plant responses to chemical and biotic stimuli. Expression of a human homolog is elevated in bladder cancer tissues. Expression patterns for At3g28950 and its Arabidopsis paralogs suggest that each one evolved a different physiological role. The At3g28950 structure was solved as part of a structural genomics effort, and the results demonstrate how such a project can further understanding of genome evolution in addition to sequence-structure and structure-function relationships. Proteins 2008. (c) 2008 Wiley-Liss, Inc.

Solution structure of a membrane-anchored ubiquitin-fold (MUB) protein from Homo sapiens.

The protein Bc059385, whose solution structure is reported here, is the human representative of a recently identified family of membrane-anchored ubiquitin-fold (MUB) proteins. Analysis of their similarity to ubiquitin indicates that homologous amino acid residues in MUBs form a hydrophobic surface very similar to the recognition patch surrounding Ile-44 in ubiquitin. This suggests that MUBs may interact with proteins containing an alpha-helical motif similar to those of some ubiquitin binding domains. A disordered loop common to MUBs may also provide a second protein interaction site. From the available data, it is probable that this protein is prenylated and associated with the membrane. With <20% identity to ubiquitin, the MUB family further expands the sequence space that maps to the beta-grasp fold, and adds membrane localization to its list of functional roles.

Structural basis of CXCR4 sulfotyrosine recognition by the chemokine SDF-1/CXCL12.

Stem cell homing and breast cancer metastasis are orchestrated by the chemokine stromal cell-derived factor 1 (SDF-1) and its receptor CXCR4. Here, we report the nuclear magnetic resonance structure of a constitutively dimeric SDF-1 in complex with a CXCR4 fragment that contains three sulfotyrosine residues important for a high-affinity ligand-receptor interaction. CXCR4 bridged the SDF-1 dimer interface so that sulfotyrosines sTyr7 and sTyr12 of CXCR4 occupied positively charged clefts on opposing chemokine subunits. Dimeric SDF-1 induced intracellular Ca2+ mobilization but had no chemotactic activity; instead, it prevented native SDF-1-induced chemotaxis, suggesting that it acted as a potent partial agonist. Our work elucidates the structural basis for sulfotyrosine recognition in the chemokine-receptor interaction and suggests a strategy for CXCR4-targeted drug development.