Two constitutional structural schemes are proposed attempting to unify and rationalize a series of focused NMR and chromatographic determinations aimed at providing an integrated picture for the structure of softwood kraft lignin.

Quick quantitative HSQC (QQ-HSQC) was applied to quantitative evaluation of different inter-unit linkages in an array of milled softwood and hardwood and technical lignins by using the guaiacyl C2 and syringyl C2-C6 signals as internal standards. The results were found to be highly reproducible and comparable with earlier literature reports. The advantage of QQ-HSQC NMR analysis of lignin is contemporary detection and quantification of lignin inter-unit linkages with a direct, non-destructive method requiring short acquisition times.

The degree of polymerization (DP) of softwood and hardwood milled wood lignin samples and their branching degrees were quantitatively evaluated by a novel end-group titration approach composed of QQ-HSQC, (31)P NMR, and DFRC coupled with (31)P NMR analysis techniques. The DP of lignin can be calculated when the C9 formula, the amounts of phenolic groups, pinoresinol (β-β), diphenylethane (β-1), and phenolic diphenyl (5-5') lignin subunits have been determined. Data on the degree of polymerization of lignin obtained by NMR techniques were not affected by supramolecular aggregation processes. (31)P NMR analysis coupled with DFRC and QQ-HSQC allowed a detailed evaluation of the occurrence of condensed units in lignin and showed the terminal nature of diphenyl ether and diphenyl subunits. The resulting data unequivocally show that milled wood lignin is a linear oligomer.

Initiation factor IF1, the smallest of the three factors, (Cummings and Hershey, 1994), indicating that one or more of the activities of IF1 must The structure of the translational initiation factor be essential for the cell. Maurizio IF1 from Escherichia coli has been determined withSeveral functions have been reported for IF1. These multidimensional NMR spectroscopy. Using 1041 disinclude: (i) the enhancement of the rate of 70S ribosome tance and 78 dihedral constraints, 40 distance geometry dissociation and subunit association (Godefroy-Colburn structures were calculated, which were refined by et al., 1975); (ii) the stimulation of the activity of IF2 restrained molecular dynamics. From this set, 19 strucand IF3 in the formation of the 30S initiation complex tures were selected, having low constraint energy and (Wintermeyer and Gualerzi, 1983; Pon and Gualerzi, few constraint violations. The ensemble of 19 structures 1984); and (iii) the modulation of the interaction of IF2 displays a root-mean-square deviation versus the averwith the ribosome, increasing its affinity for the 30S age of 0.49 Å for the backbone atoms and 1.12 Å for ribosomal subunit when IF1 is bound and indirectly all atoms for residues 6-36 and 46-67. The structure favouring its release when IF1 is ejected (Stringer et al., of IF1 is characterized by a five-stranded β-barrel.1977; Celano et al., 1988). In addition, by binding to the The loop connecting strands three and four contains a A-site of the 30S ribosomal subunit, IF1 may contribute short 3 10 helix but this region shows considerably to the fidelity of the selection of the initiation site of the higher flexibility than the β-barrel. The fold of IF1 is mRNA (Moazed et al., 1995). very similar to that found in the bacterial cold shock Equilibrium binding studies have shown that IF1 binds proteins CspA and CspB, the N-terminal domain of to the 30S ribosomal subunit in a 1:1 ratio (Zucker and aspartyl-tRNA synthetase and the staphylococcal Hershey, 1986;Celano et al., 1988). The binding affinity nuclease, and can be identified as the oligomer-binding depends strongly upon the ionic strength and upon the motif. Several proteins of this family are nucleic acidpresence of IF2 and IF3 which increase its affinity for the binding proteins. This suggests that IF1 plays its role ribosome; the K a ranging from 5ϫ10 5 to 2.5ϫ10 8 M -1 . in the initiation of protein synthesis by nucleic acid Interaction with 50S ribosomal subunits was also observed, interactions. Specific changes of NMR signals of IF1 but the affinity is considerably lower than for the 30S upon titration with 30S ribosomal subunit identifies ribosomal subunits. Stable interaction with 70S ribosomes several residues that are involved in the interaction has never been observed; in fact, the addition of 50S to with ribosomes.

The salivary antimicrobial peptide histatin-5 is able to aggregate and fuse negatively charged small unilamellar vesicles, and this fusogenic activity is selectively induced by the presence of zinc ions. Circular dichroism spectroscopy shows that histatin-5, in the presence of negatively charged vesicles and zinc ions, undergoes a conformational change leading to the stabilization of an alpha-helical secondary structure. We attribute the specific action of the zinc ions to the presence of a consensus sequence, HEXXH, located in the C-terminal functional domain of histatin-5, a recognized zinc-binding motif in many proteins. Two-dimensional proton NMR spectroscopy of histatin-5 in a trifluoroethanol/water mixture (a membrane mimetic environment) has been performed and the results analyzed by means of distance geometry and restrained molecular dynamics simulations. Our results reveal that the peptide chain, including the Zn-binding consensus sequence corresponding to residues 15-19, is in a helicoidal conformation. Comparison of the chemical shifts of the individual amino acids in histatin-5 with those recently reported in other solvents indicates that trifluoroethanol/water has a structuring capability somewhere between water and dimethyl sulfoxide. The mechanism of action of this antimicrobial peptide is discussed on the basis of its structural characteristics with particular attention to the Zn-binding motif.