Biomedical subjects

P Lubini

Publications and source records attributed to P Lubini.

4 recordsLinked to original sources

PubMed2000

Ab initio structure determination of the lantibiotic mersacidin.

The crystal structure of mersacidin, a potential novel antibiotic against methicillin- and vancomycin-resistant Staphylococcus aureus strains, has been determined by ab initio methods. Despite all crystals being merohedrally twinned, an accurate structural model with an R value of 13.4% has been obtained at atomic resolution. With six molecules in the asymmetric unit and no atom heavier than sulfur, the structure corresponds to a protein of 120 amino acids and is the largest approximately equal-atom unknown structure solved by direct methods. In the crystal, the molecule assumes a compact fold different from that found by NMR in solution. Comparison of the NCS-related molecules reveals regions of variable flexibility. The region highly homologous to the related antibiotic actagardine is very rigid and possibly defines an essential building block of this class of new antibacterial substances.

Alanine↗

PubMed1999

Ab initio solution and refinement of two high-potential iron protein structures at atomic resolution.

The crystal structure of the reduced high-potential iron protein (HiPIP) from Chromatium vinosum has been redetermined in a new orthorhombic crystal modification, and the structure of its H42Q mutant has been determined in orthorhombic (H42Q-1) and cubic (H42Q-2) modifications. The first two were solved by ab initio direct methods using data collected to atomic resolution (1.20 and 0. 93 A, respectively). The recombinant wild type (rc-WT) with two HiPIP molecules in the asymmetric unit has 1264 protein atoms and 335 solvent sites, and is the second largest structure reported so far that has been solved by pure direct methods. The solutions were obtained in a fully automated way and included more than 80% of the protein atoms. Restrained anisotropic refinement for rc-WT and H42Q-1 converged to R(1) = summation operator||F(o)| - |F(c)|| / summation operator|F(o)| of 12.0 and 13.6%, respectively [data with I > 2sigma(I)], and 12.8 and 15.5% (all data). H42Q-2 contains two molecules in the asymmetric unit and diffracted only to 2.6 A. In both molecules of rc-WT and in the single unique molecule of H42Q-1 the [Fe(4)S(4)](2+) cluster dimensions are very similar and show a characteristic tetragonal distortion with four short Fe-S bonds along four approximately parallel cube edges, and eight long Fe-S bonds. The unique protein molecules in H42Q-2 and rc-WT are also very similar in other respects, except for the hydrogen bonding around the mutated residue that is at the surface of the protein, supporting the hypothesis that the difference in redox potentials at lower pH values is caused primarily by differences in the charge distribution near the surface of the protein rather than by structural differences in the cluster region.

Animals↗

PubMed1997

The bi-loop, a new general four-stranded DNA motif.

The crystal structure of the cyclic octanucleotide d contains two independent molecules that form a novel quadruplex by means of intermolecular Watson-Crick A.T pairs and base stacking. A virtually identical quadruplex composed of G.C pairs was found by earlier x-ray analysis of the linear heptamer d(GCATGCT), when the DNA was looped in the crystal. The close correspondence between these two structures of markedly dissimilar oligonucleotides suggests that they are both examples of a previously unrecognized motif. Their nucleotide sequences have little in common except for two separated 5'-purine-pyrimidine dinucleotides forming the quadruplex, and by implication these so-called "bi-loops" could occur widely in natural DNA. Such structures provide a mechanism for noncovalent linking of polynucleotides in vivo. Their capacity to associate by base stacking, demonstrated in the crystal structure of d(GCATGCT), creates a compact molecular framework made up of four DNA chains within which strand exchange could take place.

Base Composition↗

PubMed1994

Stabilizing effects of the RNA 2'-substituent: crystal structure of an oligodeoxynucleotide duplex containing 2'-O-methylated adenosines.

BACKGROUND: The stability of hybrids of 2'-O-methyl-ribonucleotides with complementary RNA is considerably higher than that of the corresponding DNA.RNA duplexes. The 2'-O-modified ribonucleotides are thus an attractive class of compounds for antisense applications. Understanding how these substituents stabilize the structure of the hybrid duplex may be important in the design of ribonucleotides with novel properties. RESULTS: The crystal structure of a dimer of the self-complementary DNA strand d(GCGT)O2'mer(A)d(TACGC), which has a 2'-O-methylated ribonucleotide incorporated at position 5, was determined at 2.1 A resolution. This strand forms a duplex with an overall A-type conformation; the methyl groups of the two modified adenosines point into the relatively wide minor groove. Both 2'-methoxy groups are hydrogen-bonded to solvent molecules. These results allowed us to build a model of a fully 2'-O-methylated RNA double helix. CONCLUSIONS: Insertion of 2'-O-modified RNA residues into a stretch of DNA can nucleate a local A-type conformation, in part because modification with a bulky residue at this position stabilizes a C3'-endo type sugar pucker. The increased stability of fully 2'-O-methylated RNA may result from hydrophobic interactions between substituents in the minor groove. As the 2'-O-methyl groups are directed into the minor groove, it may be worthwhile to introduce tailor-made 2'-O-substituents into RNA; it might be possible to design groups that both stabilize the hybrid duplexes and carry a nuclease function, further improving the efficacy of these modified RNAs in antisense applications.

Adenosine↗