The complete primary structure of pilin fromHaemophilus influenzae type b strain Eagan

Adherence ofHaemophilus influenzae type b (Hib) to human oropharyngeal cells is mediated by pili which are proteinaceous filaments that extend outward from the bacterial cell surface. Pili from Hib strain Eagan were purified, and the primary structure of the major subunit, pilin, was determined. Sequencing of overlapping peptides showed the mature protein to be comprised of 196 amino acids and to have an M_r of 21,152. The amino terminal sequence was found to be homologous with the sequence previously reported for Hib strain M43 and also to have significant homology to pilins of other gram-negative pathogenic bacteria. Furthermore, Hib pilin had two cysteinyl residues in the amino terminal portion of the protein which were separated by 40 residues (positions 21 and 61); a motif found in other bacterial pilins. The data show that Hib pilin has structural features common to other bacterial pilins.     

Hydrogen peroxide scavenging is not a virulence determinant in the pathogenesis of Haemophilus influenzae type b strain Eagan

Background  

A potentially lethal flux of hydrogen peroxide (H₂O₂) is continuously generated during aerobic metabolism. It follows that aerobic organisms have equipped themselves with specific H₂O₂ dismutases and H₂O₂ reductases, of which catalase and the alkyl hydroperoxide reductase (AhpR) are the best-studied prokaryotic members. The sequenced Haemophilus influenzae Rd genome reveals one catalase, designated HktE, and no AhpR. However, Haemophilus influenzae type b strain Eagan (Hib), a causative agent of bacterial sepsis and meningitis in young children, disrupted in its hktE gene is not attenuated in virulence, and retains the ability to rapidly scavenge H₂O₂. This redundancy in H₂O₂-scavenging is accounted for by peroxidatic activity which specifically uses glutathione as the reducing substrate.     

The role of lic2B in lipopolysaccharide biosynthesis in Haemophilus influenzae strain Eagan

Lipopolysaccharide (LPS) biosynthesis in Haemophilus influenzae involves genes from the lic2 locus that are required for chain extension from the middle heptose (HepII) of the conserved triheptosyl inner-core moiety. Lic2C initiates the process by attaching the first glucose to HepII, but the gene encoding for the enzyme adding the next β-d-Glcp- is uncharacterized. Lic2B is the candidate glucosyltransferase; however, in previous investigations, mutation of lic2B resulted in no hexose extension from HepII, likely due to a polar effect on the lic2C gene.In this study we complemented a lic2B knock-out mutant of H. influenzae strain Eagan with a functional lic2C gene and investigated its LPS by mass spectrometry and 2D NMR spectroscopy. Lic2B was found to encode a glucosyltransferase responsible for the linkage of β-d-Glcp-(1→4)-α-d-Glcp-(1→ extending from O-3 of the central heptose of the triheptosyl inner-core moiety, l-α-d-Hepp-(1→2)-[PEtn→6]-l-α-d-Hepp-(1→3)-l-α-d-Hepp-(1→5)-[PPEtn→4]-α-Kdo-(2→6)-lipid A.     

Structural elucidation of the major Hex4 lipopolysaccharide glycoform from the lgtC mutant of Haemophilus influenzae strain Eagan

Lipopolysaccharide (LPS) oligosaccharide epitopes are major virulence factors of Haemophilus influenzae. The structure of LPS glycoforms of H. influenzae type b strain Eagan containing a mutation in the gene lgtC is investigated. LgtC is involved in the biosynthesis of globoside trisaccharide [alpha-D-Galp-(1-->4)-beta-d-Galp-(1-->4)-beta-D-Glcp-(1-->], an LPS epitope implicated in the virulence of this organism. Glycose and methylation analyses provided information on the composition while electrospray ionization mass spectrometry (ESI-MS) on O-deacylated LPS (LPS-OH) indicated the major glycoform to contain 4 hexoses attached to the common H. influenzae triheptosyl inner-core unit. The structure of the Hex4 glycoform in LPS-OH and core oligosaccharide samples was determined by NMR. It consists of an l-alpha-D-HepIIIp-(1-->2)-[PEtn-->6]-l-alpha-D-HepIIp-(1-->3)-l-alpha-D-HepIp-(1-->5)-[P-->4]-alpha-D-Kdop-(2--> to which a beta-D-Glcp-(1-->4)-alpha-D-Glcp disaccharide unit is extended from HepII at the C-3 position, while HepI and HepIII are substituted at the C-4 and C-2 positions with beta-D-Glcp and beta-D-Galp, respectively. This structure corresponds to that expressed as a subpopulation in the parent strain. 31P NMR studies permitted the identification of subpopulations of LPS containing Kdo substituted at the C-4 position with monophosphate or pyrophosphoethanolamine (PPEtn). HepIII was found to be substituted with either phosphate at the C-4 position or acetate at the C-3 position, but not both of them together in the same subpopulation. The subpopulations containing phosphate and acetate at HepIII and their location have not previously been reported.     

Haemophilus influenzae type b strain A2 has multiple sialyltransferases involved in lipooligosaccharide sialylation

The lipooligosaccharide (LOS) of Haemophilus influenzae contains sialylated glycoforms, and a sialyltransferase, Lic3A, has been previously identified. We report evidence for two additional sialyltransferases, SiaA, and LsgB, that affect N-acetyllactosamine containing glycoforms. Mutations in genes we have designated siaA and lsgB affected only the sialylated glycoforms containing N-acetylhexosamine. A mutation in siaA resulted in the loss of glycoforms terminating in sialyl-N-acetylhexosamine and the appearance of higher molecular weight glycoforms, containing the addition of phosphoethanolamine, N-acetylgalactosamine, and N-acetylneuraminic acid. Chromosomal complementation of the siaA mutant resulted in the expression of the original sialylated LOS phenotype. A mutation in lic3A resulted in the loss of sialylation only in glycoforms lacking N-acetylhexosamine and had no effect on sialylation of the terminal N-acetyllactosamine epitope. A double mutant in siaA and lic3A resulted in the complete loss of sialylation of the terminal N-acetyllactosamine epitope and expression of the higher molecular weight sialylated glycoforms seen in the siaA mutant. Mutation of lsgB resulted in persistence of sialylated glycoforms but a reduction in N-acetyllactosamine containing glycoforms. A triple mutant of siaA, lic3A, and lsgB contained no sialylated glycoforms. These results demonstrate that the sialylation of the LOS of H. influenzae is a complex process involving multiple sialyltransferases.     

The complete primary structure of HLA-Bw58

Serological studies indicate that HLA-B17 molecules are unusually cross-reactive with products of the HLA-A locus. In particular, a mouse monoclonal antibody MA2.1 defines an epitope that is shared by HLA-A2 and the two subtypes (Bw57 and Bw58) of B17. To investigate these relationships at the structural level, we have isolated a gene coding for Bw58 from the WT49 B cell line. The gene was transfected into mouse L cells and its protein product was characterized with a panel of monoclonal anti-HLA antibodies. The nucleotide sequence of 3520 base pairs of DNA encompassing the seven exons coding for Bw58 and associated introns was determined. The deduced protein sequences for Bw58 and eight other HLA-A,B,C molecules were compared. In the first polymorphic domain (alpha 1), Bw58 is unusual in that it is as homologous to HLA-A locus products as to HLA-B locus products. In the second polymorphic domain (alpha 2), Bw58 has greater homology to B locus products. In the alpha 1 domain of Bw58, small segments of amino acid and nucleotide sequence homology with A2 (residues 62-65) and with Aw24 (residues 75-83) are found in the major region of polymorphic diversity (residues 62-83). These similarities provide structural correlates for the serological relationships between Bw58 and A locus molecules, with residues 62-65 possibly being involved in the MA2.1 epitope. From comparisons of four HLA-A and four HLA-B sequences, there is a difference in the patterns of variation for A and B locus molecules. For B locus molecules there is greater variation in the alpha 1 domain than in the alpha 2 domain. For A locus molecules, variation in the two domains is similar and like that for B locus alpha 2 domains. In comparison to other HLA-A,B,C genes, novel inverted repeat sequences were found in the nucleotide sequence of HLA-Bw58. These sequences flank the putative RNA splicing sites at the 3' end of the exons encoding the alpha 2 and alpha 3 protein domains.     

Lipoproteins of Haemophilus influenzae type b.

Haemophilus influenzae type b Minn A produced 12 lipoproteins with apparent molecular weights of between 14,000 and 67,000. The lipoproteins were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography of delipidated extracts of cells grown in [3H]palmitate. When the delipidated cell extracts were subjected to acid methanolysis, tritium was quantitatively recovered as palmitate and methyl palmitate, indicating that the [3H]palmitate had not been degraded and reincorporated into nonlipid material during cell growth. One of the lipoproteins comigrated with outer membrane protein (OMP) P6. OMP P6 was purified from [3H]palmitate-labeled cells. The purified protein preparation contained both amide- and ester-linked fatty acids. We conclude that (i) H. influenzae type b produces several lipoproteins, and (ii) one of these lipoproteins is OMP P6, a protein under consideration as a vaccine component.     

Transport of hemin byHaemophilus influenzae type b

Haemophilus influenzae may be distinguished from other gram-negative bacteria by its growth requirement for hemin. The ability of this bacterium to accumulate hemin while growing in a fully defined medium has been partially characterized.Haemophilus influenzae type b ATCC 9795 transported hemin at a rate of 1.2 pmol/min/10⁹ cells during logarithmic growth. The kinetics of active transport of doubly radiolabeled hemin indicated that both iron and the porphyrin ring were taken up at the same rate. Hemin satisfied some of the total iron requirement ofHaemophilus as determined by starving the cells for iron with the addition of ethylenediamine-di-(o-hydroxyphenylacetic acid) (EDDA) and by limiting the porphyrin supply. Outer membrane proteins were compared from cells grown under hemin sufficiency versus cells grown under hemin starvation: in the latter case, a protein of molecular weight 43,000 was present in enhanced amounts; this protein may play a role in the permeability of hemin across the cell envelope ofH. influenzae type b.     

Haemophilus influenzae type b polysaccharide-protein conjugate vaccine

An Haemophilus influenzae type b capsular polysaccharide-protein conjugate has been prepared. The polysaccharide was coupled to the serotype II protein of group B meningococcus through the spacer 6-aminocaproic acid using cyanogen bromide and water soluble carbodiimide. The conjugate can be shown to be reproducible and is stable and highly immunogenic in mice and African green monkeys. Clinical evaluation of this conjugate in children 3 months to 4 years of age showed that it elicited an antibody titer to the polysaccharide moiety greater than 1000 ng/ml in children 8 months of age or older.     

Outer membrane porin protein of Haemophilus influenzae type b: pore size and subunit structure

The 40-kDa porin protein of Haemophilus influenzae type b was reconstituted into proteoliposomes. The relative rates of diffusion of small uncharged sugars across the channels formed by this protein were determined by measuring the rates of osmotic swelling of the liposomes. From these rates, a pore diameter of 1.8 nm was estimated using the Renkin equation. A chemical cross-linking technique was used to investigate the oligomeric structure of the 40-kDa porin. Sodium dodecyl sulfate - polyacrylamide gel electrophoresis revealed the presence of porin dimers and trimers after reaction of the protein with dithio-bis-(succinimidyl propionate). These results confirmed that the porin of H. influenzae forms large water-filled channels and indicated that it probably exists as trimers in the outer membrane.     

Identification of a novel structural motif in the lipopolysaccharide of the galE/galK double mutant of Haemophilus influenzae strain Eagan

Defined mutants of the galactose biosynthetic (Leloir) pathway were employed to investigate lipopolysaccharide (LPS) oligosaccharide expression in Haemophilus influenzae type b strain Eagan. The structures of the low-molecular-mass LPS glycoforms from strains with mutations in the genes that encode galactose epimerase (galE) and galactose kinase (galK) were determined by NMR spectroscopy on O- and N-deacylated and dephosphorylated LPS-backbone, and O-deacylated oligosaccharide samples in conjunction with electrospray mass spectrometric, glycose and methylation analyses. The structural profile of LPS glycoforms from the galK mutant was found to be identical to that of the galactose and glucose-containing Hex5 glycoform previously identified in the parent strain [Masoud, H.; Moxon, E. R.; Martin, A.; Krajcarski, D.; Richards, J. C. Biochemistry1997, 36, 2091-2103]. LPS from the H. influenzae strain bearing mutations in both galK and galE (galE/galK double mutant) was devoid of galactose. In the double mutant, Hex3 and Hex4 glycoforms containing di- and tri-glucan side chains from the central heptose of the triheptosyl inner-core unit were identified as the major glycoforms. The triglucoside chain extension, β-d-Glcp-(1→4)-β-d-Glcp-(1→4)-α-d-Glcp, identified in the Hex4 glycoform has not been previously reported as a structural element of H. influenzae LPS. In the parent strain, it is the galactose-containing trisaccharide, β-d-Galp-(1→4)-β-d-Glcp-(1→4)-α-d-Glcp, and further extended analogues thereof, that substitute the central heptose. When grown in galactose deficient media, the galE single mutant was found to expresses the same population of LPS glycoforms as the double mutant.     

The complete primary structure of bovine stefin B.

A new stefin B-type low-Mr CPI was isolated from bovine thymus and subjected to structural analysis. The inhibitor consisted of 98 amino acids and its Mr was calculated to be 11,178. The NH2-terminal amino acid residue was blocked. The sequence was determined by automated sequencing of peptides derived by cleavage with cyanogen bromide and fragments of the inhibitor resulting from enzymatic digestion with beta-trypsin and Staphylococcus aureus V-8 proteinase. The NH2-terminal blocking group was established with mass spectrometry. The inhibitor exhibits considerable sequence homology with inhibitors from the stefin family. Furthermore, a highly conserved QVVAG region within the stefin family is for the first time replaced by the QLVAG sequence.