Biomedical subjects

Bart Hazes

Publications and source records attributed to Bart Hazes.

6 recordsLinked to original sources

PubMed2004

Crystallographic analysis of the Pseudomonas aeruginosa strain K122-4 monomeric pilin reveals a conserved receptor-binding architecture.

Adherence of pathogens to host cells is critical for the initiation of infection and is thus an attractive target for anti-infective therapeutics and vaccines. In the opportunistic human pathogen Pseudomonas aeruginosa, host-cell adherence is achieved predominantly by type IV pili. Analysis of several clinical strains of P. aeruginosa reveals poor sequence conservation between pilin genes, including the residues in the receptor-binding site. Interestingly, the receptor-binding sites appear to retain a conserved surface epitope because all Pseudomonas type IV pili recognize the same receptor on the host cell and cross-reactive antibodies specific for the receptor-binding site exist. Here, we present the crystallographic analysis of two crystal forms of truncated pilin from P. aeruginosa strain K122-4 (DeltaK122-4) at 1.54 and 1.8 A resolution, respectively. The DeltaK122-4 structure is compared to other crystallographically determined type IV pilin structures and an NMR structure of DeltaK122-4 pilin. A comparison with the structure of the highly divergent P. aeruginosa strain K (DeltaPAK) pilin indicates that the receptor-binding loop in both pilins forms a shallow depression with a surface that is formed by main-chain atoms. Conservation of this putative binding site is independent of the sequence as long as the main-chain conformation is conserved and could therefore explain the shared receptor specificity and antibody cross reactivity of highly divergent Pseudomonas type IV pilins.

Binding Sites↗

PubMed2003

Reciprocal transfer of class I MHC allele specificity between activating Ly-49P and Ly-49W receptors by exchange of beta 4-beta 5 loop residues.

Receptors of the Ly-49 multigene family regulate rodent NK cell functions. Ly-49Rs are highly polymorphic and exist in either activating or inhibitory forms. Examples of both Ly-49 receptor types have been shown to recognize class I MHC ligands. Ly-49Rs can distinguish between class I alleles, but the molecular basis of this discrimination is unknown. Two activating receptors, Ly-49P and Ly-49W, differ in class I recognition, recognizing H-2D(d), or H-2D(d) and D(k), respectively. In this report, we demonstrate that specificity for H-2D(k) can be transferred from Ly-49W to Ly-49P by substituting 3 aa predicted to reside in the beta4-beta5 loop of Ly-49W into Ly-49P. Replacement of these same residues of Ly-49W with corresponding residues in Ly-49P eliminates H-2D(k) recognition while still preserving H-2D(d) recognition. Further mutagenesis indicates that all 3 aa facilitate optimal class I specificity exchange. These results provide the first evidence for a specific site on Ly-49Rs, the beta4-beta5 loop, in determining class I MHC allele specificity.

Alleles↗

PubMed2003

When less is more: a more efficient vapour-diffusion protocol.

Reducing protein consumption during crystallization screening is of utmost importance to crystallographers because of the time, effort and money that goes into producing pure protein. One approach is to reduce sample volumes with robotics, but a patent and the high cost of equipment limits access. Here, it is shown that the same result can be obtained by reducing the sample concentration in a modified vapour-diffusion protocol, the dilution method. In this protocol, the protein and mother liquor in the crystallization drop are both diluted, while the mother liquor in the well remains undiluted. Vapour diffusion will shrink the initial volume of the crystallization drop, e.g. 1 micro l or more, to a drop size equivalent to one dispensed by a robot. This new crystallization method circumvents some of the current problems associated with robotic crystallization screening trials. Because of the large initial volume of the crystallization drop, the evaporation problem is eliminated and dispensing accuracy is improved. In addition, the likelihood that the crystallization experiment starts in the undersaturated region is increased.

Aldose-Ketose Isomerases↗

PubMed2003

Purification, crystallization and preliminary diffraction studies of the Pseudomonas aeruginosa strain K122-4 monomeric pilin.

The monomeric pilin from Pseudomonas aeruginosa strain K122-4 has been crystallized and preliminary X-ray diffraction data have been collected. Pilin is the monomeric subunit of the type IV pilus, the dominant adhesin of the opportunistic pathogen P. aeruginosa. The K122-4 pilin crystallizes as a dimer in space group P1, with unit-cell parameters a = 40.19, b = 38.93, c = 37.22 A, alpha = 66.38, beta = 111.12, gamma = 93.74 degrees. Diffraction data were collected using a synchrotron-radiation source and were processed to 1.54 A d-spacing.

Adhesins, Bacterial↗

PubMed2003

C-terminal amino acids of Helicobacter pylori alpha1,3/4 fucosyltransferases determine type I and type II transfer.

The alpha1,3/4 fucosyltransferase (FucT) enzyme from Helicobacter pylori catalyzes fucose transfer from donor GDP-beta-l-fucose to the GlcNAc group of two series of acceptor substrates in H. pylori lipopolysaccharide: betaGal1,3betaGlcNAc (Type I) or betaGal1,4betaGlcNAc (Type II). Fucose is added either in alpha1,3 linkage of Type II acceptor to produce Lewis X or in alpha1,4 linkage of Type I acceptor to produce Lewis A, respectively. H. pylori FucTs from different strains have distinct Type I or Type II substrate specificities. FucT in H. pylori strain NCTC11639 has an exclusive alpha1,3 activity because it recognizes only Type II substrates, whereas FucT in H. pylori strain UA948 can utilize both Type II and Type I acceptors; thus it has both alpha1,3 and alpha1,4 activity, respectively. To identify elements conferring substrate specificity, 12 chimeric FucTs were constructed by domain swapping between 11639FucT and UA948FucT and characterized for their ability to transfer fucose to Type I and Type II acceptors. Our results indicate that the C-terminal region of H. pylori FucTs controls Type I and Type II acceptor specificity. In particular, the highly divergent C-terminal portion, seven amino acids DNPFIFC at positions 347-353 in 11639FucT, and the corresponding 10 amino acids CNDAHYSALH at positions 345-354 in UA948FucT, controls the Type I and Type II acceptor recognition. This is the opposite of mammalian FucTs where acceptor preference is determined primarily by the N-terminal residues in the hypervariable stem domain.

Amino Acid Sequence↗

PubMed2002

Allelic variation in the ectodomain of the inhibitory Ly-49G2 receptor alters its specificity for allogeneic and xenogeneic ligands.

The Ly-49 multigene receptor family regulates mouse NK cell functions. A number of Ly-49 genes exhibit allelic variation, but the functional significance of allelic differences in extracellular domains of Ly-49 receptors regarding ligand specificity is largely unknown. Amino acid differences exist in the extracellular domains of the B6 and BALB/c allele products of the inhibitory Ly-49G receptor. We constructed chimeric Ly-49 receptors consisting of common cytoplasmic and transmembrane regions of the activating Ly-49W receptor fused with the ectodomains of the B6 and BALB/c alleles of Ly-49G. Expression of these chimeras in the RNK-16 rat NK cell line allowed us to study the specificity of inhibitory receptor ectodomains as they stimulated NK lytic activity. We found that the ectodomain of the BALB/c allele of Ly-49G recognizes both H-2D(d) and D(k) class I MHC alleles, whereas the ectodomain of the B6 allele of Ly-49G recognizes D(d), and not D(k). The specificity for D(k) as well as D(d) of the wild-type Ly-49G(BALB/c) allele product was confirmed with RNK-16 transfectants of this inhibitory receptor. Furthermore, the ectodomain of the Ly-49G(BALB/c) allele recognizes a distinct repertoire of xenogeneic ligands that only partially overlaps with that recognized by Ly-49G(B6). Our results indicate that allelic variation in Ly-49 extracellular domains can have functional significance by altering Ly-49 receptor specificity for mouse class I MHC and xenogeneic ligands.

Alleles↗