Whereas much of organic chemistry has classically dealt with the preparation and study of the properties of individual molecules, an increasingly significant portion of the activity in chemical research involves understanding and utilizing the nature of the interactions bet w e n molecules. Two representative areas of this evolution are supramolecular chemistry and molecular recognition. The interactions between molecules are governed by intermolecular forces whose energetic and geometric properties are much less well understood than those of classical chemical bonds between atoms. Among the strongest of these interactions, however, are hydrogen bonds, whose directional properties are better understood on the local level (that is, for a single hydrogen bond) than many other types of nonbonded interactions. Nevertheless, the means by which to characterize, understand, and predict the consequences of many hydrogen bonds among molecules, and the resulting formation of molecular aggregates (on the microscopic scale) or crystals (on the macroscopic scale) has remained largely enigmatic. One of the most promising systematic approaches to resolving this enigma was initially developed by the late M. C. Etter, who applied graph theory to recognize, and then utilize, patterns of hydrogen bonding for the understanding and design of molecular crystals. In working with Etter's original ideas the power and potential utility of this approach on one hand, and on the other, the need to develop and extend the initial Etter formalism was generally recognized. It with that latter purpose that we originally undertook the present review.

No abstract

deren Freundschaft in ihre Tage als Mannschaftskameraden im Softball-Team des Yale University Chemistry Department Anfang der sechziger Jahre zuriickreicht.Muster von H-Brucken in organischen Kristallen pladiertL2 -' 1. Es gab betrachtliches Interesse an dieser MethodeC7]. und es erschien uns notwendig, unsere fruheren formalen Darstellungen der Regeln zur Bestimmung von Graphensatzen zu erweitern. Dariiber hinaus erkannten wir in dem MaDe, in dem wir selbst Erfahrungen sammelten, und als Ergebnis zahlreicher Anfragen anderer, die ebenfalls versuchten, diese Methoden anzuwenden, eine Reihe von Problemen, MiBverstandnissen und Zweideutigkeiten in den Anleitungen, die fruher zur Bestimmung der Graphensatze gegeben worden ~a r e n [~' 'I. Wir hielten es daher fur angebracht, diese Regeln hier unter mehr praktischen Gesichtspunkten zusammenzufassen und eine Reihe von Beispielen zu prasentieren, die zusatzliche Hilfestellung geben und als Richtlinie fur diejenigen dienen konnten, die diese Methode anwenden mochten.Es ist uns wohl bewuBt, daB sich der graphentheoretische Ansatz, sol1 er von Nutzen sein, einer klaren und einheitlichen Sprache bedienen muD. Bestimmungen, die Anwender an verschiedenen Orten treffen, mussen auf klar verstandlichen und allgemein anerkannten Regeln beruhen, sie mussen einfach zu treffen und reproduzierbar sein. Ein Weg, diese Situation zu garantieren, ware, allgemein zugangliche Computerprogramme zur Verfugung zu stellen, um die Ermittlung von Graphensatzen zu unterstutzen. Dies ist sicherlich ein Ziel, das wir anstreben,uiid wir arbeiten zur Zeit auch an der Entwicklung von Software, die diesen Anforderungen gerecht wird. In der Zwischenzeit halten wir es jedoch fur wichtig, die Verbreitung von MiBverstandnissen und falschen Vorstellungen iiber die Arbeit mit dieser Methode und ihre Anwendungsmoglichkeiten zu verhindern; ebenso mochten wir die Weitergabe von falsch bestimmten Graphensatzen vermeiden. Dies waren die Grunde fur uns, diese Veroffentlichung zu schreiben. Wir werden zuerst kurz die wesentlichen Merkmale des graphentheoretischen Ansatzes zusammenfassen, dabei aber auf den bereits veroffentlichten, mehr formalen Ansatz verweisen. AnschlieRend folgt eine Reihe von ausgearbeiteten Beispielen fur die Ermittlung von Graphensltzen, wobei wir auch auf einige Schwierigkeiten und Fallstricke sowie deren Vermeidung eingehen mochten. Zum SchluR mochten wir die Nutzlichkeit der graphentheoretischen Analyse bei der Entdeckung der Funktionalitat von H-Brucken-Mustern diskutieren, die die traditionellen Grenzen chemischer Funktionalitat iiberschreiten. Die Definition yon GraphensatzenVielleicht das Bemerkenswerteste am graphentheoretischen Ansatz zur Analyse von H-Brucken-Mustern ist die Tatsache, daR selbst komplizierte molekulare Netzwerke auf Kombinationen aus vier Mustern reduziert werden konnen, die durch Designatoren beschrieben werden: Ketten (C), Ringe (R), Muster von intramolekularen H-Briicken (S) und andere finite Muster (D). Die Spezifikation eines Musters wird erweitert durch die Z...

No abstract

Inherited retinal degeneration due to loss of photoreceptor cells is a leading cause of human blindness. These cells possess a photosensitive outer segment linked to the cell body through the connecting cilium (CC). While structural defects of the CC have been associated with retinal degeneration, its nanoscale molecular composition, assembly, and function are barely known. Here, using expansion microscopy and electron microscopy, we reveal the molecular architecture of the CC and demonstrate that microtubules are linked together by a CC inner scaffold containing POC5, CENTRIN, and FAM161A. Dissecting CC inner scaffold assembly during photoreceptor development in mouse revealed that it acts as a structural zipper, progressively bridging microtubule doublets and straightening the CC. Furthermore, we show that Fam161a disruption in mouse leads to specific CC inner scaffold loss and triggers microtubule doublet spreading, prior to outer segment collapse and photoreceptor degeneration, suggesting a molecular mechanism for a subtype of retinitis pigmentosa.

We presented an extensible multidimensional sensor with conjugated nonspecific dye-labeled DNA sequences absorbed onto gold nanoparticles (DNA-AuNPs) as receptors. At the presence of target protein, DNA was removed from the surface of AuNPs due to the competitive binding, which resulted in a red-to-blue color change along with salt-induced aggregation of AuNPs for colorimetric analysis and fluorescent "turn-on" signal of the labeled dye for fluorescence analysis. The orthogonal and complementary fluorescent and colorimetric signals obtained from each protein were applied to distinguish different proteins. By simply changing the DNA sequences, more dual-channel sensing elements could be easily obtained and added into this multidimensional sensor. This enhanced its discriminating power to the proteins. With three sensing elements, our extensible multidimensional sensing platform exhibited excellent discrimination ability. Eleven proteins at the concentration of 50 nM had been classified with accuracies of 100% by using linear discriminant analysis (LDA). Remarkably, two similar proteins [bovine serum albumin (BSA) and human serum albumin (HSA)] at various concentrations and the mixture of these two proteins with different molar ratios had been successfully discriminated in one LDA plot as well. Furthermore, in the presence of human urine sample, 10 proteins at 1.0 μM could also be well-discriminated. The accuracy of discrimination of unknown samples was all 100% for these experiments. This strategy is a complement of the multidimensional sensing system and traditional sensor platform, offering a new way to develop sensitive array sensing systems.

Chloroplasts divide by binary fission, which is accomplished by the simultaneous constriction of the FtsZ ring on the stromal side of the inner envelope membrane, and the ARC5 ring on the cytosolic side of the outer envelope membrane. The two rings are connected and coordinated mainly by the interaction between the inner envelope membrane protein ARC6 and the outer envelope membrane protein PDV2 in the intermembrane space. The underlying mechanism of this coordination is unclear to date. Here, we solved the crystal structure of the intermembrane space region of the ARC6-PDV2 complex. The results indicated that PDV2 inserts its carboxy terminus into a pocket formed in ARC6, and this interaction further induces the dimerization of the intermembrane space regions of two ARC6 molecules. A pdv2 mutant attenuating PDV2-induced ARC6 dimerization showed abnormal morphology of ARC6 rings and compromised chloroplast division in plant cells. Together, our data reveal that PDV2-induced dimerization of ARC6 plays a critical role in chloroplast division and provide insights into the coordination mechanism of the internal and external plastid division machineries.

In all organisms the only known ab initio pathway leading to synthesis of myoinositol is conversion of D-glucose-6-phosphate to L-myo-inositol-1-phosphate (via inositol-1-phosphate synthase, IPS), followed by specific dephosphorylation via inositol monophosphatase (IMPase). We have investigated both enzymes involved in synthesis of myo-inositol in the hyperthermophilic sulfate reducer Archaeoglobus fulgidus. The structures of both enzymes were obtained to better than 2 Å resolution. The structure solution process and the resulting structures of both enzymes will be described in detail and compared with corresponding enzymes from other species. Insights into catalysis and possible evolutionary changes will be discussed. In particular, we will focus on the use of metal ions in the IPS catalytic cycle and the basis for dual activity of the IMPase.