Brassinosteroids (BRs) are essential phytohormones that play crucial roles in plant growth and development. Perception of BRs requires an active complex of brassinosteroid-insensitive 1 (BRI1) and BRI1-associated kinase 1 (BAK1). Recognized by the extracellular leucine-rich repeat (LRR) domain of BRI1, BRs induce a phosphorylation-mediated cascade to regulate gene expression. Here we present the crystal structures of BRI1-LRR in free and brassinolide (BL)-bound forms. BRI1-LRR exists as a monomer in crystals and solution independent of BL. It comprises a helical solenoid structure that accommodates a separate insertion domain at its concave surface. Sandwiched between them, BL binds to a hydrophobicity-dominating surface groove on BRI1-LRR. BL recognition by BRI1-LRR is through an induced-fit mechanism involving stabilization of two inter-domain loops that creates a pronounced non-polar surface groove for the hormone binding. Together, our results define the molecular mechanisms by which BRI1 recognizes BRs and provide insight into BR-induced BRI1 activation.

Recent studies have unequivocally associated the fat mass and obesity-associated (FTO) gene with the risk of obesity. In vitro FTO protein is an AlkB-like DNA/RNA demethylase with a strong preference for 3-methylthymidine (3-meT) in single-stranded DNA or 3-methyluracil (3-meU) in single-stranded RNA. Here we report the crystal structure of FTO in complex with the mononucleotide 3-meT. FTO comprises an amino-terminal AlkB-like domain and a carboxy-terminal domain with a novel fold. Biochemical assays show that these two domains interact with each other, which is required for FTO catalytic activity. In contrast with the structures of other AlkB members, FTO possesses an extra loop covering one side of the conserved jelly-roll motif. Structural comparison shows that this loop selectively competes with the unmethylated strand of the DNA duplex for binding to FTO, suggesting that it has an important role in FTO selection against double-stranded nucleic acids. The ability of FTO to distinguish 3-meT or 3-meU from other nucleotides is conferred by its hydrogen-bonding interaction with the two carbonyl oxygen atoms in 3-meT or 3-meU. Taken together, these results provide a structural basis for understanding FTO substrate-specificity, and serve as a foundation for the rational design of FTO inhibitors.

SUMMARY To infect plants, Pseudomonas syringae pv. tomato delivers ~30 type III effector proteins into host cells, many of which interfere with PAMP-triggered immunity (PTI). One effector, AvrPtoB, suppresses PTI using a central domain to bind host BAK1, a kinase that acts with several pattern recognition receptors to activate defense signaling. A second AvrPtoB domain binds and suppresses the PTI-associated kinase Bti9 but is conversely recognized by the protein kinase Pto to activate effector-triggered immunity. We report the crystal structure of the AvrPtoB-BAK1 complex, which revealed structural similarity between these two AvrPtoB domains, suggesting that they arose by intragenic duplication. The BAK1 kinase domain is structurally similar to Pto, and a conserved region within both BAK1 and Pto interacts with AvrPtoB. BAK1 kinase activity is inhibited by AvrPtoB, and mutations at the interaction interface disrupt AvrPtoB virulence activity. These results shed light on a structural mechanism underlying host-pathogen coevolution.

BackgroundThe chemokine receptors CXCR4 and CCR7 play an important role in cancer invasion and metastasis. This study investigated the expression of CXCR4, CCR7, CXCL12, CCL21, and EGFR to illustrate the role of these biomarkers in breast cancer metastasis and prognosis.MethodsThe CXCR4, CCR7, CXCL12, CCL21, and EGFR biomarkers were analyzed along with ER, PR, and HER-2/neu in breast cancer tissue microarray (TMA) specimens, including 200 primary breast cancer specimens by immunohistochemistry. Corresponding lymph nodes from the same patients were also examined using the same method.ResultsTogether with their CXCL12 and CCL21 ligands, CXCR4 and CCR7 were significantly highly expressed in tumor cells with lymph node (LN) metastasis. Similarly, EGFR was expressed highly in tumors with LN metastasis. The ligands were especially expressed in metastatic tumors than in primary tumors from the same patients. Moreover, the expression of both CXCR4 accompanied by CCR7 and CXCL12 accompanied by CCL21 were up-regulated. Kaplan-Meier survival analysis revealed that patients exhibiting high CXCR4, CCR7, and EGFR expression experienced a shorter survival period compared with those with low expression.ConclusionsThe expression of CXCR4, CCR7, and EGFR may be associated with LN metastasis. Moreover, the expression of these receptors can serve as an indicator of undesirable prognosis in patients with breast cancer.

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