Isolation, purification and characterization of histidino-threosidine, a novel Maillard reaction protein crosslink from threose, lysine and histidine

We isolated a novel acid-labile yellow chromophore from the incubation of lysine, histidine and d-threose and identified its chemical structure by one and two-dimensional NMR spectroscopy combined with LC-tandem mass spectrometry. This new cross-link exhibits a UV absorbance maximum at 305 nm and a molecular mass of 451 Da. The proposed structure is 2-amino-5-(3-((4-(2-amino-2-carboxyethyl)-1H-imidazol-1-yl)methyl)-4-(1,2-dihydroxyethyl)-2-formyl-1H-pyrrol-1-yl)pentatonic acid, a cross-link between lysine and histidine with addition of two threose molecules. It was in part deduced and confirmed through synthesis of the analogous compound from n-butylamine, imidazole and d-threose. We assigned the compound the trivial name histidino-threosidine. Systemic incubation revealed that histidino-threosidine can be formed in low amounts from fructose, glyceraldehyde, methylglyoxal, glycolaldehyde, ascorbic acid, and dehydroascorbic acid, but at a much higher yield with degradation products of ascorbic acid, i.e. threose, erythrose, and erythrulose. Bovine lens protein incubated with 10 and 50 mM threose for two weeks yielded 560 and 2840 pmol/mg histidino-threosidine. Histidino-threosidine is to our knowledge the first Maillard reaction product known to involve histidine in a crosslink.     

Body shape vs. colour associated initial divergence in the Telmatherina radiation in Lake Matano, Sulawesi, Indonesia

Highly polymorphic colouration patterns are often associated with sexual selection in fish and can be the initial cause of divergence among closely related taxa. Here we use genetic, body colour and geometric morphometric data collected on 118 fish from Lake Matano, Sulawesi, Indonesia to test if colouration is the initial cause of divergence in the radiating Telmatherina genus. Results reveal that all Telmatherina previously described in this system can be categorized into three mitochondrial lineages and that colouration is only weakly associated with early divergence. Clade-specific body shapes, however, likely adapted to microenvironments are key to the initial divergence in this system. Data also show that although colourations were not likely instrumental in seeding divergence in these fish, they appear to have developed in parallel within each clade. Our results are consistent with an emerging pattern repeated in many vertebrate radiations, whereby divergence by colouration or other display traits is preceded by specialization to environmental adaptive peaks.     

Chiroptical properties and conformation of chiral enamines of 2-(2′-pyrido,or quinolino) acetophenone

CD study of the chiral enamines 4-9 revealed the presence of the azastil-bene-like chromophore, and exciton coupling between this chromophore (A) and aromatic chromophore B . Coupled excitons in 5 and 8 suggest M (−) absolute conformation between chromophores A and B . © 1996 Wiley-Liss, Inc.     

Chirality sensing of bioactive compounds with amino alcohol unit via circular dichroism

The aim of the present work was to test various chiroptical techniques, including in particular the in situ dirhodium methodology, to assign the absolute configuration of 1,2‐ and 1,3‐amino alcohols. As models, we selected mainly compounds that have both an additional strongly absorbing and interfering chromophoric system and application in medicinal chemistry. Determination of the absolute configuration (AC) of the tested molecules such as cinchona alkaloids, Tamiflu, and others was carried out using a combination of electronic and vibrational circular dichroism (ECD, VCD) spectroscopy. It has been demonstrated that both 1,2‐ and 1,3‐aminol moieties are subject to the same sector rule correlating stereostructure of formed Rh₂‐complex with chiroptical properties, and that the changes in the position of the stereogenic center do not affect its proper use.     

A spitting image: specializations in archerfish eyes for vision at the interface between air and water

Archerfish are famous for spitting jets of water to capture terrestrial insects, a task that not only requires oral dexterity, but also the ability to detect small camouflaged prey against a visually complex background of overhanging foliage. Because detection of olfactory, auditory and tactile cues is diminished at air–water interfaces, archerfish must depend almost entirely on visual cues to mediate their sensory interactions with the aerial world. During spitting, their eyes remain below the water''s surface and must adapt to the optical demands of both aquatic and aerial fields of view. These challenges suggest that archerfish eyes may be specially adapted to life at the interface between air and water. Using microspectrophotometry to characterize the spectral absorbance of photoreceptors, we find that archerfish have differentially tuned their rods and cones across their retina, correlated with spectral differences in aquatic and aerial fields of view. Spatial resolving power also differs for aquatic and aerial fields of view with maximum visual resolution (6.9 cycles per degree) aligned with their preferred spitting angle. These measurements provide insight into the functional significance of intraretinal variability in archerfish and infer intraretinal variability may be expected among surface fishes or vertebrates where different fields of view vary markedly.     

A modified equilibrium dialysis method for studying fatty acid binding to proteins

A modified equilibrium dialysis method is described which is suitable for investigating the binding of fatty acids in the form of aqueous micellar dispersions to proteins. The method uses a permeant chromophore which complexes reversibly with free fatty acid within the dialysis bag. The concentration outside the dialysis bag is determined spectrophotometrically. Binding of oleic acid to bovine serum albumin is given as an example. A simplified analysis of fatty acid binding is given and used to indicate the potential of the method.     

Synthesis and spectroscopic properties of 4-ethoxymethylene-2-(1)-naphthyl-5(4H)-oxazolone-labeled fluorescent peptides

Strategies for the preparation of new fluorescent oligopeptide conjugates labeled with 4-ethoxymethylene-2-[1]-naphthyl-5(4H)-oxazolone (naOx-OEt) at the N-terminal on solid support or in solution have been devised. These procedures are simple and easy to carry out by reacting naOx-OEt or N(alpha)-naOx-amino acid with side chain protected peptide chains attached to resins. The integrity of the N-alkyl bond was maintained even after the trifluoracetic acid or HF based cleavages procedures. Our data show that the naOx fluorophore is compatible with both Fmoc/tBu and Boc/Bzl methods and also suggest that naOx-amino acid could be utilized as building blocks for solid phase peptide synthesis. Comparative analysis of fluorescence properties of naOx-conjugates indicated that the spectral properties of the fluorophore do not change after incorporating into peptides. The compact size, the definite chemical reaction for its introduction in combination with the appropriate spectral features (e.g., intense emission, pH independent fluorescent characteristics, and beneficial photobleaching dose constant and rates) and with chemical and spectral stability, naOx-based labeling could be attractive for novel cellular fluorescent techniques (e.g., in laser scanning confocal FRET) to study peptide-protein and protein-protein interactions even in biological matrices.     

Unique Mechanisms of Excitation Energy Transfer, Electron Transfer and Photoisomerization in Biological Systems

We discuss unique mechanisms typical in the elementary processes ofbiological functions. We focus on three topics. Excitation energytransfer in the light-harvesting antenna systems of photosyntheticbacteria is unique in its structure and the energy transfer mechanism. Inthe case of LH2 of Rhodopseudomonas acidophila, the B850 intra-ringenergy transfer and the inter-ring energy transfer between B800 and B850take place by the intermediate coupling mechanism of energy transfer. Theexcitonic coherent domain shows a wave-like movement along the ring, andthis property is expected to play a significant role in the inter-ringenergy transfer between LH2's. The electron transfer in biological systemsis mostly long-range electron transfer that occurs by the electrontunneling through the protein media. There is a long-standing problem thatwhich part of protein media is used for the electron tunneling root. As aresult of our detailed analysis, we found that the global electron tunnelingroot is a little winded with a width of a few angstrom, reflecting theproperty of tertiary and secondary structures of the protein and it isaffected by the thermal fluctuation of protein structure. Photoisomerizationof rhodopsin is very unique: The cis-transphotoisomerization ofrhodopsin occurs only around the C11 = C12 bond in the counterclockwisedirection. Its molecular mechanism is resolved by our MD simulation studyusing the structure of rhodopsin which was recently obtained by the X-raycrystallographic analysis.     

含Dsred类似生色团的红色荧光蛋白的发展及应用

自从绿色荧光蛋白(GFP)被发现以来,荧光蛋白在生物医学领域已经成为一种重要的荧光成像工具．随着红色荧光蛋白DsRed的出现,各种优化的DsRed突变体和远红荧光蛋白也不断涌现．其中荧光蛋白生色团的形成机制对改建更优的荧光蛋白变种影响很大,对于红色荧光蛋白而言,大多数的红色荧光蛋白的生色团类型为DsRed类似生色团,在此基础上又出现了Far-red DsRed类似生色团．目前,含DsRed类似生色团的荧光蛋白主要有单体红色荧光蛋白、光转换荧光蛋白、斯托克斯红移蛋白、荧光计时器等．这些优化的荧光蛋白作为分子探针可以实现对活细胞、细胞器或胞内分子的时空标记和追踪,已经在生物工程学、细胞生物学、基础医学领域得到广泛应用．本文综述了含DsRed类似生色团的荧光蛋白的研究进展及其应用,以及由此发展起来的远红荧光蛋白在活体显微成像技术中的应用,并展望了荧光探针技术研究的新方向．     

Structural Basis of Stable Bending in DNA Containing An Tracts. Different Types of Bending

Abstract

Structural determinants of DNA bending of different types have been studied by theoretical conformational analysis of duplexes. Their terminal parts were fixed either in an ordinary low-energy B-like conformation or in “anomalous” conformations with a narrowed minor groove typical of A_n tracts. The anomalous conformations had different negative tilt angles (up to about zero), different propeller twists and minor groove widths. Calculations have been performed for DNA fragments A_nT_m, T_nA_m, A_nGCT_m, A_nCGT_m, T_mGCA_n, T_mCGA_n which are the models of the junction of two anomalous structures on A_n and T_m tracts. On the AT step of the A_nT_m fragment the minor groove can be easily narrowed so that a whole unbent fragment of anomalous structure is formed on A_n T_m. According to our energy estimates, there should not be any reliable bending on A_nT_m. In contrast, in all other cases there was a pronounced roll-like bending into the major groove in the chemical symmetry region. Calculations of the junction between the anomalous and ordinary B-like structure for G_nT_m and C_nA_m have shown that there is an equilibrium bending with a tilt component towards the chain having the anomalous structure at the 5′-end. From our calculations it is impossible to determine precisely the direction of bending, though it can be suggested that the roll component of bending might be directed towards the major groove. The anomalous structure is the main reason of bending; alternations of pyrimidines and purines can modulate the value and the direction of equilibrium bending (only the value in the case of self-complemantary fragments).

The results are consistent with the experimental data and promote a better understanding of the problem of DNA bending.