Studying protein-protein interactions using peptide arrays

Screening of arrays and libraries of compounds is well-established as a high-throughput method for detecting and analyzing interactions in both biological and chemical systems. Arrays and libraries can be composed from various types of molecules, ranging from small organic compounds to DNA, proteins and peptides. The applications of libraries for detecting and characterizing biological interactions are wide and diverse, including for example epitope mapping, carbohydrate arrays, enzyme binding and protein-protein interactions. Here, we will focus on the use of peptide arrays to study protein-protein interactions. Characterization of protein-protein interactions is crucial for understanding cell functionality. Using peptides, it is possible to map the precise binding sites in such complexes. Peptide array libraries usually contain partly overlapping peptides derived from the sequence of one protein from the complex of interest. The peptides are attached to a solid support using various techniques such as SPOT-synthesis and photolithography. Then, the array is incubated with the partner protein from the complex of interest. Finally, the detection of the protein-bound peptides is carried out by using immunodetection assays. Peptide array screening is semi-quantitative, and quantitative studies with selected peptides in solution are required to validate and complement the screening results. These studies can improve our fundamental understanding of cellular processes by characterizing amino acid patterns of protein-protein interactions, which may even develop into prediction algorithms. The binding peptides can then serve as a basis for the design of drugs that inhibit or activate the target protein-protein interactions. In the current review, we will introduce the recent work on this subject performed in our and in other laboratories. We will discuss the applications, advantages and disadvantages of using peptide arrays as a tool to study protein-protein interactions.     

On solution of higher approximations to boundary layer flows

Résumé Pour trouver des approximations d'un ordre élevé dans les problèmes de couche limite, l'auteur propose une méthode qui unifie le approches de Meksyn et Görtler. Les valeurs initiales, pour les approximations successives de Görtler, sont evaluées à l'aide de la methode de Meksyn. Toutes les valeurs initiales sont obtaneues par différentiation d'une seule équation. Les résultats obtenus sont au moins équivalent à ceux obtenus par la méthode de Hsu, avec considérablement moins de calculs.     

Synthesis and Stereochemical Assignment of Crypto‐Optically Active 2H6‐Neopentane

The determination of the absolute configuration of chiral molecules is at the heart of asymmetric synthesis. Here we probe the spectroscopic limits for chiral discrimination with NMR spectroscopy in chiral aligned media and with vibrational circular dichroism spectroscopy of the sixfold‐deuterated chiral neopentane. The study of this compound presents formidable challenges since its stereogenicity is only due to small mass differences. For this purpose, we selectively prepared both enantiomers of ²H₆‐ 1 through a concise synthesis utilizing multifunctional intermediates. While NMR spectroscopy in chiral aligned media could be used to characterize the precursors to ²H₆‐ 1 , the final assignment could only be accomplished with VCD spectroscopy, despite the fleetingly small dichroic properties of 1 . Both enantiomers were assigned by matching the VCD spectra with those computed with density functional theory.     

Suzuki-miyaura cross-coupling of 1,1-dichloro-1-alkenes with 9-alkyl-9-BBN

We addressed an unexplored application of the Suzuki-Miyaura protocol to the cross-coupling of 1,1-dichloro-1-alkenes with 9-alkyl-9-BBN. The use of bisphosphine ligands with a large P-Pd-P bite angle allowed us to synthesize Z-chlorinated internal alkenes in good yields resulting from a selective monocoupling process, a recurrent challenge with 1,1-dichloro-1-alkenes. Moreover, these monochlorinated olefins could be further transformed providing stereospecifically trisubstituted olefins.     

Bacterial and eukaryotic phenylalanyl-tRNA synthetases catalyze misaminoacylation of tRNA(Phe) with 3,4-dihydroxy-L-phenylalanine

Aminoacyl-tRNA synthetases exert control over the accuracy of translation by selective pairing the correct amino acids with their cognate tRNAs, and proofreading the misacylated products. Here we show that three existing, structurally different phenylalanyl-tRNA synthetases-human mitochondrial (HsmtPheRS), human cytoplasmic (HsctPheRS), and eubacterial from Thermus thermophilus (TtPheRS), catalyze mischarging of tRNA(Phe) with an oxidized analog of tyrosine-L-dopa. The lowest level of L-dopa discrimination over the cognate amino acid, exhibited by HsmtPheRS, is comparable to that of tyrosyl-tRNA synthetase. HsmtPheRS and TtPheRS complexes with L-dopa revealed in the active sites an electron density shaping this ligand. HsctPheRS and TtPheRS possessing editing activity are capable of hydrolyzing the exogenous L-dopa-tRNA(Phe) as efficiently as Tyr-tRNA(Phe). However, editing activity of PheRS does not guarantee reduction of the aminoacylation error rate to escape misincorporation of L-dopa into polypeptide chains.     

Compacted UHMWPE fiber composites: Morphology and X‐ray microdiffraction experiments

The effect of compaction conditions on UHMWPE fibers is examined by microbeam X‐ray diffraction (WAXS) and scanning electron microscopy (SEM). The morphological observations indicate that melting occurs during compaction both on the surface of the fiber as well as in its internal regions. In addition, the recrystallized phase is nucleated on the fiber surface, possibly epitaxially. The recrystallized phase that originates from the internal regions of the fiber retains the initial highly oriented structure. WAXS microbeam measurements do not show any significant core‐shell structure in compacted single fibers. Considering the overall characteristics of the melting process during compaction, we can conclude that the hexagonal phase that appears upon heating of the fibers under moderate pressure is responsible for good adhesion of the fibers to each other, even more significantly than surface melting, especially because of its ability to retain the high orientation of the chains in the fibers. This information is relevant for understanding the formation and microstructure of the matrix component in the self‐reinforced composites fabricated by compaction. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1535–1541, 2007