Integrins are important mammalian receptors involved in normal cellular functions as well as pathogenesis of chronic inflammation and cancer. We propose that integrins are exploited by the gastric pathogen and type-1 carcinogen Helicobacter pylori for injection of the bacterial oncoprotein cytotoxin-associated gene A (CagA) into gastric epithelial cells. Virulent H. pylori express a type-IV secretion pilus that injects CagA into the host cell; CagA then becomes tyrosine-phosphorylated by Src family kinases. However, the identity of the host cell receptor involved in this process has remained unknown. Here we show that the H. pylori CagL protein is a specialized adhesin that is targeted to the pilus surface, where it binds to and activates integrin alpha5beta1 receptor on gastric epithelial cells through an arginine-glycine-aspartate motif. This interaction triggers CagA delivery into target cells as well as activation of focal adhesion kinase and Src. Our findings provide insights into the role of integrins in H.-pylori-induced pathogenesis. CagL may be exploited as a new molecular tool for our further understanding of integrin signalling.

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Apomyoglobin undergoes a two-step unfolding transition when the pH is lowered from 6 to 2. The partly folded intermediate (I) state at pH 4 and low ionic strength has properties of a molten globule. We have studied structural features of this state, its compactness, content of secondary structure, and specific packing of aromatic side chains, using dynamic light scattering, and small-angle X-ray scattering and far- and near-ultraviolet circular dichroism spectroscopy. Particular attention was paid to temperature-dependent structural changes. The results are discussed with reference to the native-like (N) state and the highly unfolded (U) state. It turned out that the I-state is most compact near 30 degrees C, having a Stokes radius 20% larger and a radius of gyration 30% larger than those of the N-state. Both cooling and heating relative to 30 degrees C led to an expansion of the molecule, but the structural changes at low and high temperatures were of a different kind. At temperatures above 40 degrees C non co-operative melting of structural elements was observed, while the secondary structure was essentially retained on cooling. The results are discussed in context with theoretical predictions of the compactness and the stability of apomyoglobin by Alonso et al. [Alonso, D. O. V., Dill, K. A., and Stigter, D. (1991) Biopolymers 31:1631-1649]. Comparing the I-state of apomyoglobin with the molten globules of alpha-lactalbumin and cytochrome c, we found that the compactness of the molten globule states of the three proteins decreases in the order alpha-lactalbumin > apocytochrome c > apomyoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)

Selected HLA-B27 subtypes are associated with spondyloarthropathies, but the underlying mechanism is not understood. To explain this association in molecular terms, a comparison of peptide-dependent dynamic and structural properties of the differentially disease-associated subtypes HLA-B*2705 and HLA-B*2709 was carried out. These molecules differ only by a single amino acid at the floor of the peptide binding groove. The thermostabilities of a series of HLA-B27 molecules complexed with nonameric and decameric peptides were determined and revealed substantial differences depending on the subtype as well as the residues at the termini of the peptides. In addition we present the crystal structure of the B*2709 subtype complexed with a decameric peptide. This structure provides an explanation for the preference of HLA-B27 for a peptide with an N-terminal arginine as secondary anchor and the lack of preference for tyrosine as peptide C terminus in B*2709. The data show that differences in thermodynamic properties between peptide-complexed HLA-B27 subtypes are correlated with a variety of structural properties.

The temperature-dependent conformational equilibrium of 3-phosphoglycerate kinase has been studied in the temperature range from 1 to 30 degrees C by means of dynamic light scattering, small-angle X-ray scattering, differential scanning calorimetry, circular dichroism spectroscopy, and fluorescence spectroscopy. At 28 degrees C and in the presence of 0.7 M guanidine hydrochloride (GuHCl), the radius of gyration (RG) and the Stokes radius (RS) are 2.44 and 3.09 nm, respectively. Decreasing the temperature effects unfolding of the molecule, a process that involves two stages. The two stages correspond to the successive unfolding of the N-terminal and C-terminal domains. The peak maxima of the excess heat capacity, determined from differential calorimetric scans, extrapolated to 0 scan rate, are positioned at 16.5 degrees C for the N-terminal domain and at 6.3 degrees C for the C-terminal domain. At 4.5 degrees C, the radius of gyration and the Stokes radius increase to 7.8 and 4.8 nm, respectively. The persistence length and the length of the statistical chain segment of the unfolded polypeptide chain are 1.74 and 3.48 nm, corresponding to five and ten amino acids, respectively. At 1 degrees C, the dimensions of the unfolded chain nearly agree with the predicted dimensions under theta conditions. Thus, the conformational changes upon cold denaturation can be described by a transition from a compactly folded molecule to a random coil. The conformation-dependent ratio rho = RGRS-1 increases from rho = 0.79 to rho = 1.63. The volume of the unfolded chain is 30 times larger than that of the folded chain in the native state.(ABSTRACT TRUNCATED AT 250 WORDS)

Raman spectra of calf thymus DNA were measured in the pH interval 6.4 to 3.45 in the presence of divalent manganese ions. pH-dependent protonation of AT and GC base pairs and conformational changes were indicated in the spectra. Protonation of adenine residues becomes obvious at pH 4.4 and continues upon lowering the pH to 3.45. Adenine protonation is connected with the disruption of AT base pairs. Protonation of GC base pairs is indicated at somewhat lower pH than that of AT base pairs, namely at pH 3.8, and continues upon lowering the pH to 3.45. At pH 3.8 unstacking of thymine residues is indicated, and spectral markers for the unstacking of adenine and cytosine were found at pH 3.45. Changes of the DNA backbone are indicated by spectral changes of conformational marker bands at 898 and 1423 cm −1 .

Initiation factor IF21 is the largest (741 amino acids in Bacillus stearothermophilus; Ref.

The secondary structure of streptokinase (Sk) in aqueous solution was quantitatively examined by using Fourier transform infrared (FT-IR) spectroscopy. Resolution enhancement techniques, including Fourier deconvolution and derivative spectroscopy, were combined with band curve-fitting procedures to quantitate the spectral information from the amide I bands. Nine component bands were found under the broad, nearly featureless amide I bands which reflect the presence of various substructures. The relative areas of these component bands indicate an amount of beta-sheet between 30 and 37% and an alpha-helix content of only 12-13% in Sk. Further conformational substructures are assigned to turns (25-26%) and to "random" structures (15-16%). Additionally, the correlation of a pronounced component band near 1640 cm-1 (10-16% fractional area) with the possible presence of 3(10)-helices is discussed.