The BBA33 lipoprotein binds collagen and impacts Borrelia burgdorferi pathogenesis

Borrelia burgdorferi, the etiologic agent of Lyme disease, adapts to the mammalian hosts by differentially expressing several genes in the BosR and Rrp2‐RpoN‐RpoS dependent pathways, resulting in a distinct protein profile relative to that seen for survival in the Ixodes spp. tick. Previous studies indicate that a putative lipoprotein, BBA33, is produced in an RpoS‐dependent manner under conditions that mimic the mammalian component of the borrelial lifecycle. However, the significance and function for BBA33 is not known. Given its linkage to the BosR/Rrp2‐RpoN‐RpoS regulatory cascade, we hypothesized that BBA33 facilitates B. burgdorferi infection in the mammalian host. The deletion of bba33 eliminated B. burgdorferi infectivity in C3H mice, which was rescued by genetic complementation with intact bba33. With regard to function, a combinatorial peptide approach, coupled with subsequent in vitro binding assays, indicated that BBA33 binds to collagen type VI and, to a lesser extent, collagen type IV. Whole cell binding assays demonstrated BBA33‐dependent binding to human collagen type VI. Taken together, these results suggest that BBA33 interacts with collagenous structures and may function as an adhesin in a process that is required to prevent bacterial clearance.     

Structure and function of herpesvirus genomes. I. comparison of five HSV-1 and two HSV-2 strains by cleavage their DNA with eco R I restriction endonuclease.

The restriction endonuclease Eco R I cleaves HSV-1 and HSV-2 DNA into specific fragments that can be resolved by agarose gel electrophoresis. Comparison of HSV-1 strains KOS, 14-012, MP, F, and CI 101, and HSV-2 strains 333 and 186, suggests that the DNAs from type 1 strains are similar but not identical, and that the type 2 strains differ greatly from type 1 strains. The molecular lengths of the fragments have been determined by electron microscopy and can be used to calibrate gel electrophoretic analyses of DNA fragments.     

Microsatellite evolution in congeneric mammals: domestic and bighorn sheep

We compared genotypes at eight (AC)n microsatellite loci in domestic sheep (Ovis aries) and wild Rocky Mountain bighorn sheep (O. canadensis). The domestic sheep had greater genetic variation, higher allele-size variances, and larger allele sizes than the wild sheep. Accumulating evidence from higher taxonomic comparisons shows that these parameters are biased if microsatellite loci are selected in one taxon and used in another. Our results demonstrate similar biases between congeneric species. We compared standard measures of genetic variation, differentiation, and distance within and between species (H, D, FST) to newer measures based on allele-size variance (SW, SB, RST). The size-based distances better detected species-level divergence, but standard measures better distinguished allopatric populations. Empirical calibration of these measures at the subspecies level is needed to establish their useful ranges.      

Porin activity of the native and recombinant outer membrane protein Oms28 of Borrelia burgdorferi.

The outer membrane-spanning (Oms) proteins of Borrelia burgdorferi have been visualized by freeze-fracture analysis but, until recently, not further characterized. We developed a method for the isolation of B. burgdorferi outer membrane vesicles and described porin activities with single-channel conductances of 0.6 and 12.6 nS in 1 M KCI. By using both nondenaturing isoelectric focusing gel electrophoresis and fast-performance liquid chromatography separation after detergent solubilization, we found that the 0.6-nS porin activity resided in a 28-kDa protein, designated Oms28. The oms28 gene was cloned, and its nucleotide sequence was determined. The deduced amino acid sequence of Oms28 predicted a 257-amino-acid precursor protein with a putative 24-amino-acid leader peptidase I signal sequence. Processed Oms28 yielded a mature protein with a predicted molecular mass of 25,363 Da. When overproduced in Escherichia coli, the Oms28 porin fractionated in part to the outer membrane. Sodium dodecyl sulfate-polyacrylamide gel-purified recombinant Oms28 from E. coli retained functional activity as demonstrated by an average single-channel conductance of 1.1 nS in the planar lipid bilayer assay. These findings confirmed that Oms28 is a B. burgdorferi porin, the first to be described. As such, it is potential relevance to the pathogenesis of Lyme borreliosis and to the physiology of the spirochete.     

A mutation in the amino terminus of a hybrid TrpC-TonB protein relieves overproduction lethality and results in cytoplasmic accumulation.

We have developed a selection for mutations in a trpC-tonB gene fusion that takes advantage of the properties of the plasmid-encoded TrpC-TonB hybrid protein. The TrpC-TonB hybrid protein consists of amino acids 1 through 25 of the normally cytoplasmic protein, TrpC, fused to amino acids 12 through 239 of TonB. It is expressed from the trp promoter and is regulated by the trpR gene and the presence or absence of tryptophan. Under repressing conditions in the presence of tryptophan, the trpC-tonB gene can restore phi 80 sensitivity to a tonB deletion mutant, which indicates that TrpC-TonB can be exported and is functional. High-level expression of TrpC-TonB protein in the absence of tryptophan results in virtually immediate cessation of growth for strains carrying the trpC-tonB plasmid. By selecting for survivors of the induced growth inhibition (overproduction lethality), we have isolated a variety of mutations. Many of the mutations decrease expression of the TrpC-TonB protein, as expected. In addition, three independently isolated mutants expressing normal levels of TrpC-TonB protein result in a Gly----Asp substitution within the hydrophobic amino terminus of TonB. The mutant proteins are designated TrpC-TonBG26D. The mutations are suppressed by prlA alleles, known to suppress export (signal sequence) mutations. TrpC-TonB proteins carrying the Gly----Asp substitution accumulate in the cytoplasm. We conclude that the Gly----Asp substitution is an export mutation. TrpC-TonBG26D protein has been purified and used to raise polyclonal antibodies that specifically recognize both TrpC-TonB protein and wild-type TonB protein.     

Early events in the cellular formation of proparathyroid hormone

Early events in the cellular synthesis and subsequent transfer into membrane-limited compartments of pre-proparathyroid hormone (pre-proPTH) and proparathyroid hormone (proPTH) were investigated by electrophoretic analyses of newly synthesized proteins in subcellular fractions of parthyroid gland slices pulse-labeled for 0.5-5 min with [(35)S] methionine. During these short times of incubation, both pre-proPTH and proPTH were confined to the microsomal fraction. Labeled pre-proPTH and proPTH were detected in a 30-s interval between 0.5 and 1.0 min of incubation. The radioactivity in proPTH became relatively constant between 3 and 5 min, whereas the radioactivity in ProPTH increased markedly over this period. When corrected for the known content of methionine in the prohormone and the prohormone, we found four times as much radiolabeled prohormone as prehormone between 0.5 and 1.0 min of synthesis. Sequestration of labeled prohomrone into endoplasmic reticulum compartments was shown by treatment of the microsomal fraction with chymotrypsin and trypsin, which resulted in the degradation of the prehormone but not of the prohormones. Approximately 50 percent of pre-prohormone and 25 percent of prohormone were released from the microsomes by their extraction with 1.0 M KCl, whereas 80-90 percent of both was released by treatment with Triton X-100. These results in intact cells support the signal hypothesis proposed by Blobel and his co-workers in studies utilizing cell-free systems, inasmuch as the results indicate transfer of prohormone into the cisternal space of the rough endoplasmic reticulum concomitant with the growth of the nascent polypeptide chain. Appearance of membrane-sequestered proPTH takes place without entry of pre-proPTH into the cisternal space, suggesting that proteolytic removal of the leader peptide occurs during transfer of the polypeptide through the lipid bilayer. Further evidence in support of this process is that pre-proPTH is only partly extracted from the microsomes by treatment with 1.0 M KCl, suggesting that a substantial fraction of the nascent pre-proPTH is integrally inserted into the membranes before it is cleaved to form proPTH.     

Sequence analysis and characterization of a 40-kilodalton Borrelia hermsii glycerophosphodiester phosphodiesterase homolog.

We report the purification, molecular cloning, and characterization of a 40-kDa glycerophosphodiester phosphodiesterase homolog from Borrelia hermsii. The 40-kDa protein was solubilized from whole organisms with 0.1% Triton X-100, phase partitioned into the Triton X-114 detergent phase, and purified by fast-performance liquid chromatography (FPLC). The gene encoding the 40-kDa protein was cloned from a B. hermsii chromosomal DNA lambda EXlox expression library and identified by using affinity antibodies generated against the purified native protein. The deduced amino acid sequence included a 20-amino-acid signal peptide encoding a putative leader peptidase II cleavage site, indicating that the 40-kDa protein was a lipoprotein. Based on significant homology (31 to 52% identity) of the 40-kDa protein to glycerophosphodiester phosphodiesterases of Escherichia coli (GlpQ), Bacillus subtilis (GlpQ), and Haemophilus influenzae (Hpd; protein D), we have designated this B. hermsii 40-kDa lipoprotein a glycerophosphodiester phosphodiesterase (Gpd) homolog, the first B. hermsii lipoprotein to have a putative functional assignment. A nonlipidated form of the Gpd homolog was overproduced as a fusion protein in E. coli BL21(DE3)(pLysE) and was used to immunize rabbits to generate specific antiserum. Immunoblot analysis with anti-Gpd serum recognized recombinant H. influenzae protein D, and conversely, antiserum to H. influenzae protein D recognized recombinant B. hermsii Gpd (rGpd), indicating antigenic conservation between these proteins. Antiserum to rGpd also identified native Gpd as a constituent of purified outer membrane vesicles prepared from B. hermsii. Screening of other pathogenic spirochetes with anti-rGpd serum revealed the presence of antigenically related proteins in Borrelia burgdorferi, Treponema pallidum, and Leptospira kirschneri. Further sequence analysis both upstream and downstream of the Gpd homolog showed additional homologs of glycerol metabolism, including a glycerol-3-phosphate transporter (GlpT), a glycerol-3-phosphate dehydrogenase (GlpD), and a thioredoxin reductase (TrxB).     

A new mutation causing familial amyloidotic polyneuropathy

The DNA from an individual with familial amyloidotic polyneuropathy was examined. It did not possess any of the mutations which have previously been associated with familial amyloidotic polyneuropathy. However, a novel 7.0 kb Sph I restriction fragment was discovered, and the mutation creating it was localized to exon 3 of the transthyretin gene. This mutation was inherited from a parent, and may result in an amino acid substitution for glu89, his90 or ala91. The patient's transthyretin has a lower pI than normal transthyretin.     

Inhibition of crossed caudal interneurons by lateral interneurons in lamprey spinal cord during fictive locomotion

Templates of the membrane potential profiles from lateral (LI) interneurons and motoneurons during glutamate- and N-methyl-D-aspartate (NMDA)-induced fictive locomotion showed pronounced plateau phases. In contrast, crossed caudal (CC) interneurons had a less obvious and steeper plateau region that was followed by a clear notch coinciding with the end of the lateral interneuron plateau phase. These results indicate a significant inhibitory input from LI to CC interneurons.