The molecular symmetry of bovine liver catalase.

A rotation function study of bovine liver catalase at 10 Å resolution has shown the enzyme to have at least one 2-fold axis, although a molecular symmetry of 222 is likely and the molecular point group 4 is possible. The orientation of the molecular axes with respect to the crystallographic axes has also been determined.     

New Pyrimidine Cyclonucleosides with Hydrogenated Aglycones: Synthesis and X-Ray Structures

Abstract

Acid catalysed transformations of (6S)-6,5′-anhydro-6-hydroxy-1-(2′,3′-O-isopropylidene-β-D-ribofuranosyl)hexahydropyrimidine-2-thione are studied. (6R)-6,2′-anhydro-6-hydroxy-1-(α-D-ribofuranosyl)hexahydropyrimidine-2-thione was formed as a thermodynamically stable product. Two intermediates, (6S)-6,5′-anhydro-6-hydroxy-1-(β-D-ribofuranosyl)hexahydropyrimidine-2-thione and 6-hydroxy-1-(D-ribosyl)hexahydropyrimidine-2-thione and products of cleavage of glycosidic bond were identified in the reaction mixtures. Results of X-ray structural determination of the synthesised nucleosides are presented.     

Interdomain interactions in aspartic proteases of higher organisms and their analogs in retroviral enzymes

On recent evidence, the efficiency of catalysis and the specificity of aspartic proteases depend considerably on the dynamic properties of particular molecular regions and their correlations. Analysis of the three-dimensional structures of these enzymes showed the presence of a continuous chain of hydrogen-bonded groups, which connects regions with highly correlated dynamic parameters and provides for a “cross-hand” interaction between domains. This chain includes the inner oxygens of the active carboxyls and the conserved internal water molecules. The so-called “fireman grip” interdomain hydrogen bonding is part of this chain. Such networks are abortive in retroviral proteases. The role of these interactions in the functions of aspartic proteases is discussed.     

Programmed type movement in patients with lesion to different cerebellar systems

The contribution of the lateral and intermediate cerebellar systems to fast voluntary movement control was investigated in man. The trial consisted of executing a series of dorsal or plantar flexions of increasing amplitude with minimal difference from that of other local movements. A close connection was found between the intermediate cerebellar system and information processing and proprioception. The lateral cerebellar system was shown to make a direct contribution to programming movements, tailoring these to the requirements of a given task. Lesioning of the pyramidal tract is accompanied by severe impairment in the execution of programmed mechanisms (or of the system of carrying out the programs): it is impossible to execute programmed movements when the pyramidal system is damaged.Institute for Disorders of Information Transmission, Academy of Sciences of the USSR, Moscow. Institute of Neurology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 233–241, March–April, 1986.     

Identification of the amino acid residues responsible for the reversible photoconversion of the monomeric red fluorescent protein TagRFP

The site-directed mutagenesis of the monomeric red fluorescent protein TagRFP and its variants was performed with the goal of generating reversibly photoactivatable fluorescent proteins. Amino acids at positions 69, 148, 165, 179, and 181 (enumeration according to the green fluorescent protein GFP) were shown to play a key role in the manifestation of the photoactivatable properties. A reversibly photoactivatable red fluorescent protein KFP-HC with excitation and emission maxima at 585 and 615 nm, respectively, was generated. The KFP-HC fluorescent intensity was decreased by 5–10 times under green light (530–560 nm) irradiation (due to the fall of the fluorescence quantum yield) and restored under irradiation with blue light (450–490 nm) or after incubation in the dark (recovery half-time of 30 min).     

Photoconversion of the Chromophore of a Fluorescent Protein from Dendronephthya sp.

A green fluorescent protein from the coral Dendronephthya sp. (Dend FP) is characterized by an irreversible light-dependent conversion to a red-emitting form. The molecular basis of this phenomenon was studied in the present work. Upon UV-irradiation at 366 nm, the absorption maximum of the protein shifted from 494 nm (the green form) to 557 nm (the red form). Concurrently, in the fluorescence spectra the emission maximum shifted from 508 to 575 nm. The green form of native Dend FP was shown to be a dimer, and the oligomerization state of the protein did not change during its conversion to the red form. By contrast, UV-irradiation caused significant intramolecular changes. Unlike the green form, which migrates in SDS-polyacrylamide gels as a single band corresponding to a full-length 28-kD protein, the red form of Dend FP migrated as two fragments of 18- and 10-kD. To determine the chemical basis of these events, the denatured red form of Dend FP was subjected to proteolysis with trypsin. From the resulting hydrolyzate, a chromophore-containing peptide was isolated by HPLC. The structure of the chromophore from the Dend FP red form was established by methods of ESI, tandem mass spectrometry (ESI/MS/MS), and NMR-spectroscopy. The findings suggest that the light-dependent conversion of Dend FP is caused by generation of an additional double bond in the side chain of His65 and a resulting extension of the conjugated system of the green form chromophore. Thus, classified by the chromophore structure, Dend FP should be referred to the Kaede subfamily of GFP-like proteins.     

A purple-blue chromoprotein from Goniopora tenuidens belongs to the DsRed subfamily of GFP-like proteins

A number of recently cloned chromoproteins homologous to the green fluorescent protein show a substantial bathochromic shift in absorption spectra. Compared with red fluorescent protein from Discosoma sp. (DsRed), mutants of these so-called far-red proteins exhibit a clear red shift in emission spectra as well. Here we report that a far-red chromoprotein from Goniopora tenuidens (gtCP) contains a chromophore of the same chemical structure as DsRed. Denaturation kinetics of both DsRed and gtCP under acidic conditions indicates that the red form of the chromophore (absorption maximum at 436 nm) converts to the GFP-like form (384 nm) by a one-stage reaction. Upon neutralization, the 436-nm form of gtCP, but not the 384-nm form, renaturates instantly, implying that the former includes a chromophore in its intact state. gtCP represents a single-chain protein and, upon harsh denaturing conditions, shows three major bands in SDS/PAGE, two of which apparently result from hydrolysis of an acylimine C=N bond. Instead of having absorption maxima at 384 nm and 450 nm, which are characteristic for a GFP-like chromophore, fragmented gtCP shows a different spectrum, which presumably corresponds to a 2-keto derivative of imidazolidinone. Mass spectra of the chromophore-containing peptide from gtCP reveal an additional loss of 2 Da relative to the GFP-like chromophore. Tandem mass spectrometry of the chromopeptide shows that an additional bond is dehydrogenated in gtCP at the same position as in DsRed. Altogether, these data suggest that gtCP belongs to the same subfamily as DsRed (in the classification of GFP-like proteins based on the chromophore structure type).     

Natural animal coloration can Be determined by a nonfluorescent green fluorescent protein homolog

It is generally accepted that the colors displayed by living organisms are determined by low molecular weight pigments or chromoproteins that require a prosthetic group. The exception to this rule is green fluorescent protein (GFP) from Aequorea victoria that forms a fluorophore by self-catalyzed protein backbone modification. Here we found a naturally nonfluorescent homolog of GFP to determine strong purple coloration of tentacles in the sea anemone Anemonia sulcata. Under certain conditions, this novel chromoprotein produces a trace amount of red fluorescence (emission lambda(max) = 595 nm). The fluorescence demonstrates unique behavior: its intensity increases in the presence of green light but is inhibited by blue light. The quantum yield of fluorescence can be enhanced dramatically by single amino acid replacement, which probably restores the ancestral fluorescent state of the protein. Other fluorescent variants of the novel protein have emission peaks that are red-shifted up to 610 nm. They demonstrate that long wavelength fluorescence is attainable in GFP-like fluorescent proteins.     

DNA-binding antibiotics. X-ray structure of the distamycin A analog.

The crystal structure of the antibiotic distamycin A analog containing two pyrrol carboxamide fragments has been determined. The space group of the crystals is P21/b; the unit-cell dimensions are a = 11.169, b = 21.535, c = 7.863 A, alpha = beta = 90 degrees, gamma = 122.45 degrees, Z = 4. The structure is solved by direct methods, and refined with the full-matrix least-squares procedure. The data on the structure of the pyrrol carboxamide backbone allow the following conclusions to be made about the molecular structure of the distamycin type antibiotics: (i) the amide groups have normal trans-configuration with slightly shortened C-C and C-N bonds adjacent to the pyrrol rings, (ii) the N-methyl groups of the pyrrol rings and the oxygen atoms of the amide groups have the same orientation with respect to the backbone. In the distamycin A analog molecule the pyrrol rings and amide group between them are approximately coplanar.