Summary Protein folding in the cell relies on the orchestrated action of conserved families of molecular chaperones, the Hsp70 and Hsp90 systems. Hsp70 acts early and Hsp90 late in the folding path, yet the molecular basis of this timing is enigmatic, mainly because the substrate specificity of Hsp90 is poorly understood. Here we obtained a structural model of Hsp90 in complex with its natural disease-associated substrate, the intrinsically disordered Tau protein. Hsp90 binds to a broad region in Tau that includes the aggregation-prone repeats. Complementarily, a 106 Å long substrate-binding interface in Hsp90 enables many low affinity contacts. It allows recognition of scattered hydrophobic residues in late folding intermediates that remain after early burial of the Hsp70 sites. Our model resolves the paradox of how Hsp90 specifically selects for late folding intermediates but also for some intrinsically disordered proteins – through the eyes of Hsp90 they look the same.

Key indicators: single-crystal X-ray study; T = 293 K; mean (C-C) = 0.003 A ˚ ; R factor = 0.045; wR factor = 0.117; data-to-parameter ratio = 14.3. In the crystal structure of the title compound, C 12 H 10 N 6 , the molecules deviate slightly from planarity. The plane of the central triazole ring makes angles of 6.13 (9) and 3.28 (10) with the pyridyl ring planes. Intramolecular N-HÁ Á ÁN interactions form six-membered closed rings. The crystal packing also shows weak C-HÁ Á Á and C-HÁ Á ÁN interactions. Related literature For related literature, see: Dirtu et al. (2007); Faulmann et al. Experimental Crystal data C 12 H 10 N 6 M r = 238.26 Monoclinic, P2 1 =c a = 6.6191 (2) A ˚ b = 14.7136 (4) A ˚ c = 11.4703 (4) A ˚ = 95.474 (2) V = 1112.01 (6) A ˚ 3 Z = 4 Mo K radiation = 0.09 mm À1 T = 293 (2) K 0.20 Â 0.13 Â 0.12 mm Data collection Bruker APEX CCD area-detector diffractometer Absorption correction: multi-scan (SADABS; Sheldrick, 2000) T min = 0.91, T max = 0.99 23253 measured reflections 2751 independent reflections 1465 reflections with I > 2(I) R int = 0.052

Chemokines orchestrate leukocyte trafficking and function in health and disease. Heterophilic interactions between chemokines in a given microenvironment may amplify, inhibit, or modulate their activity; however, a systematic evaluation of the chemokine interactome has not been performed. We used immunoligand blotting and surface plasmon resonance to obtain a comprehensive map of chemokine-chemokine interactions and to confirm their specificity. Structure-function analyses revealed that chemokine activity can be enhanced by CC-type heterodimers but inhibited by CXC-type heterodimers. Functional synergism was achieved through receptor heteromerization induced by CCL5-CCL17 or receptor retention at the cell surface via auxiliary proteoglycan binding of CCL5-CXCL4. In contrast, inhibitory activity relied on conformational changes (in CXCL12), affecting receptor signaling. Obligate CC-type heterodimers showed high efficacy and potency and drove acute lung injury and atherosclerosis, processes abrogated by specific CCL5-derived peptide inhibitors or knock-in of an interaction-deficient CXCL4 variant. Atheroprotective effects of CCL17 deficiency were phenocopied by a CCL5-derived peptide disrupting CCL5-CCL17 heterodimers, whereas a CCL5 α-helix peptide mimicked inhibitory effects on CXCL12-driven platelet aggregation. Thus, formation of specific chemokine heterodimers differentially dictates functional activity and can be exploited for therapeutic targeting.

Amyloid is the result of an anomalous protein and peptide aggregation, leading to the formation of insoluble fibril deposits. At present, 18 human diseases have been associated with amyloid deposits-e.g., Alzheimer's disease and Prion-transmissible Spongiform Encephalopathies. The molecular structure of amyloid is to a large extent unknown, because of lack of high-resolution structural information within the amyloid state. However, from other experimental data it has been established that amyloid fibrils predominantly consist of ␤-strands arranged perpendicular to the fibril axis. Identification of residues involved in these secondary structural elements is therefore of vital importance to rationally designing appropriate inhibitors. We have designed a hydrogen͞ deuterium exchange NMR experiment that can be applied on mature amyloid to enable identification of the residues located inside the fibril core. Using a highly amyloidogenic peptide, corresponding to residues 25-35 within the Alzheimer A␤(1-43) peptide, we could establish that residues 28 -35 constitute the amyloid core, with residues 31 and 32 being the most protected. In addition, quantitative values for the solvent accessibility for each involved residue could be obtained. Based on our data, two models of peptide assembly are proposed. The method provides a general way to identify the core of amyloid structures and thereby pinpoint areas suitable for design of inhibitors.A myloid diseases have in common an abnormal folding of normally soluble proteins resulting in the formation of extracellular amyloid deposits (1). Examples are Alzheimer's Disease, Prion-transmissible Spongiform Encephalopathies, and Familial Amyloidotic Polyneuropathy (2). Through selfassembly these proteins produce regular fibrillar structures possessing a predominant ␤-sheet conformation (3). Structural information on the core of fibrils has mainly been elucidated from fiber-diffraction studies (4), mass-spectrometry (5), and solid-state NMR spectroscopy (6), resulting in a general picture consistent with parallel or antiparallel ␤-strands, placed perpendicularly to the fibril axis. However, a detailed structure of a fibril at the atomic level is still lacking. In this respect, more structural information-e.g., which specific amino acids make up the amyloid-forming core-becomes crucially important.In this article, we describe a NMR approach to determining the sequence-specific structural elements in the fibril stage of amyloid forming proteins. The method relies on the partial solvent protection of hydrogen-bonded amide protons connecting the ␤-strands throughout the length of the fibril. In aqueous solutions it is expected that amide protons located on the exterior of the fibril are more accessible to solvent and therefore experience a higher hydrogen exchange rate than amide protons buried within the fibril interior. Studies using mass spectrometry, in combination with deuterium exchange, have already pointed to this possibility (7). However, mass spectrometry does not allow spe...