Biomedical subjects

T Borén

Publications and source records attributed to T Borén.

7 recordsLinked to original sources

PubMed1992

Actinomyces tissue specificity may depend on differences in receptor specificity for GalNAc beta-containing glycoconjugates.

Actinomyces naeslundii 12104 and A. viscosus LY7 were compared for receptor specificities and adherence properties because these relate to their oral colonization sites. Both strains bind GalNAc beta-containing glycosphingolipids (GSLs) in a GalNAc beta 1-3Gal alpha Oethyl-sensitive fashion but differ with respect to the number of cells bound to GSLs and the effect of neighboring sugar groups on the binding. Their hemagglutination and saccharide inhibition profiles confirms the existence of two receptor specificities (for example, when GalNAc beta 1-3Gal alpha Oethyl is multivalently conjugated to albumin, its inhibitory activity increases fourfold toward strain 12104 but decreases fourfold toward strain LY7). Trypsin or chymotrypsin treatment of human erythrocytes, which possess receptor GSLs, improves their hemagglutination with strain 12104. In contrast, the same treatment of chicken erythrocytes, which lack receptor GSLs, abolishes their hemagglutination. These findings suggest that both GSLs and glycoproteins act as functional receptors on eukaryotic cells. The strains also differ with respect to the following GalNAc beta 1-3Gal alpha Oethyl-sensitive adherence properties: (i) strain LY7 adheres somewhat better than does strain 12104 to buccal epithelial cells; (ii) in spite of their similar overall coaggregation patterns with streptococci, strain 12104 coaggregates with Streptococcus oralis MPB1 but strain LY7 does not; (iii) strain 12104 alone shows GalNAc beta-sensitive saliva aggregation and adherence to saliva-coated hydroxyapatite. The GSL binding patterns of fresh Actinomyces isolates reveal a high prevalence of LY7-like specificities among buccal isolates, whereas 12104-like specificities are most prevalent among plaque isolates. These findings strongly suggest that fresh Actinomyces isolates use fine specificity for GalNAc beta-containing glycoconjugates in recognition and subsequent colonization of specific oral surfaces.

Acetylgalactosamine↗

PubMed1992

Salivary receptors for GalNAc beta-sensitive adherence of Actinomyces spp.: evidence for heterogeneous GalNAc beta and proline-rich protein receptor properties.

The receptors for GalNAc beta 1-3Gal alpha Oethyl (GalNAc beta)-sensitive adherence of Actinomyces strains to salivary pellicles were investigated. Parotid and submaxillary saliva from one individual was size fractionated and utilized in hydroxyapatite adherence assays with Actinomyces naeslundii 12104 and A. viscosus 19246 and LY7 with and without GalNAc beta. Three parotid salivary fractions, the high-molecular-weight, acidic proline-rich protein (PRP), and statherin fractions, promote GalNAc beta-sensitive adherence of strain 12104, whereas only the high-molecular-weight fraction of submaxillary saliva promotes such adherence. In contrast, strain LY7, possessing a variant GalNAc beta specificity, shows GalNAc beta-sensitive adherence to the leading and trailing regions of the submaxillary PRP fractions but less distinct adherence to the parotid and submaxillary high-molecular-weight fractions. In addition, the PRP and statherin fractions promote adherence of strains LY7 and 19246 that is not inhibited by GalNAc beta. However, whereas strain LY7 binds more strongly to the PRP fraction than to the statherin fraction, strain 19246 binds preferentially to the statherin fractions of parotid and submaxillary saliva. These salivary protein fractions were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunostained to detect glycosylated proteins. The different salivary receptor properties are paralleled by different glycosylation patterns. The variable GalNAc beta specificities may have evolved to match different salivary glycosylation patterns, and PRP and statherin binding properties seem to be heterogeneous among the Actinomyces strains.

Acetylgalactosamine↗

PubMed1990

Codon reading properties of an unmodified transfer RNA.

We have previously shown that the Mycoplasma mycoides glycine tRNA (anticodon UCC) effectively reads the codons GGU and GGC in violation of the classic codon reading rules. We have attempted to elucidate what structural elements in this tRNA molecule confer this translational property and in the course of this investigation T7 RNA polymerase transcription of the corresponding gene was used to produce a tRNA devoid of modified nucleosides. Using an in vitro translation system the ability of this tRNA to read the 4 glycine codons (GGU, GGC, and GGG) was tested and it was shown to be as efficient as its normal, fully modified counterpart in the reading of all four codons. This result demonstrates that a tRNA devoid of modified nucleosides is able to efficiently sustain protein synthesis in vitro and, furthermore, that the normal modification pattern of the Mycoplasma glycine tRNA is not essential for the ability of this tRNA to read the glycine codons GGU and GGC effectively.

Base Sequence↗

PubMed1989

Codon discrimination and anticodon structural context.

Site-directed mutagenesis has been used to change the nucleotide C in the wobble position of tRNA(1Gly) (CCC) to U. The mutated tRNA was tested for its ability to read glycine codons in an in vitro protein-synthesizing system programmed with the phage message MS2-RNA that had been modified by site-directed mutagenesis so as to make it possible to monitor conveniently the reading of all four glycine codons. The results showed that while the efficiency of tRNA(1Gly) (UCC) was comparable to that of mycoplasma tRNA(Gly) (UCC) in the reading of the codon GGA, the mycoplasma tRNA(Gly) was far more efficient than the tRNA(1Gly) (UCC) in the reading of the codons GGU and GGC. Thus, the anticodon UCC, when present in the structural context of the tRNA(1Gly) molecule, behaved as predicted by the wobble rules while in the structural context of the mycoplasma tRNA(Gly) it read without discrimination between the nucleotides in the third codon position, in violation of the wobble restrictions. The result with the codon GGG showed that the anticodon UCC, when present in tRNA(1Gly), was considerably less efficient in reading this codon than it was in the structural context of the mycoplasma tRNA(Gly). It would therefore seem that the anticodon UCC, when present in a certain tRNA, can be an efficient wobbler, while in the molecular environment of another tRNA it is markedly restricted in its ability to wobble.

Amino Acid Sequence↗

PubMed1988

Properties of a transfer RNA lacking modified nucleosides.

A transfer RNA complete devoid of modified nucleosides was synthesized by in vitro transcription, and some of its properties in aminoacylation and protein synthesis in vitro were studied. For this purpose, a plasmid was constructed which contained a glycine tRNA gene from Mycoplasma mycoides under the promoter of the T7 RNA polymerase, as well as a BstNI restriction site at the 3'-end of the tRNA gene. Cleavage of plasmid DNA with BstNI followed by T7 RNA polymerase transcription in vitro yielded an RNA which was processed with M1 RNA, the catalytic subunit of ribonuclease P, to give a tRNA of mature length. The tRNA synthesized in this manner can be esterified with glycine in vitro, and the rate of aminoacylation is the same as when using the corresponding fully modified glycine tRNA from M. mycoides. Furthermore, in protein synthesis in vitro, the tRNA lacking modified nucleosides was essentially as efficient as the corresponding normal glycine tRNA. However, the Escherichia coli extract used in our protein-synthesizing system introduced one modification, pseudouridine, into the in vitro-synthesized tRNA, and it cannot be excluded that this modification has an essential role in protein synthesis.

Adenosine↗

PubMed1987

Apparent lack of discrimination in the reading of certain codons in Mycoplasma mycoides.

We report a cluster of four tRNA genes from Mycoplasma mycoides as well as the sequence of the alanine, proline, and valine tRNAs and the serine tRNA reading the UCN codons (where N stands for G, A, C, or U). This brings the total number of tRNA genes that we have so far characterized in this organism to 14, 6 of which code for tRNAs that read the codons of family boxes. In each of these latter cases, we found only one gene per family box, and the gene sequence contains a thymidine in the position corresponding to the wobble nucleotide, with the exception of the arginine tRNA gene that has an adenosine in this position. Furthermore, all of the tRNA structures reported here have an unsubstituted uridine in the wobble position. These findings are similar to those reported for mitochondria, especially yeast mitochondria, that contain an arginine tRNA with the anticodon ACG. However, the resemblance is not complete since we have demonstrated the presence of two isoacceptor tRNAs for threonine having uridine and adenosine, respectively, in the wobble position. It is suggested that in the M. mycoides at least some of the family codon boxes are read by only one tRNA each, using an unconventional method without discrimination between the nucleotides in the third codon position.

Base Sequence↗

PubMed1983

Unconventional reading of the glycine codons.

We have used a protein-synthesizing in vitro system programmed with the phage message MS2-RNA to investigate the ability of glycyl-tRNAs with different anticodons to read the glycine codons. Under conditions of no competition, when the glycyl-tRNA analyzed was the only source of glycine for protein synthesis, each of the isoacceptors tested, tRNA1Gly (anticodon CCC), tRNA2Gly (anticodon N/UCC), tRNA3Gly (anticodon GCC) from Escherichia coli, and tRNAGly (anticodon UCC) from Mycoplasma mycoides, could read all of the glycine codons in the MS2 coat protein cistron (GGU, GGC, GGA, and GGG). However, tRNA1Gly seemed to have difficulties reading through the whole cistron. Experiments in which two glycyl-tRNAs competed for the same codon showed that the mycoplasma tRNAGly (anticodon UCC) was almost as efficient in the unorthodox reading of the codons GGU and GGC as it was in conventional reading. It would seem to be the only tRNAGly present in Mycoplasma mycoides and our results are consistent with this finding since the mycoplasma tRNAGly appears to have been designed to read all four glycine codons with approximately equal efficiency. The competition experiments furthermore showed that E. coli tRNA1Gly (anticodon CCC) reads the codon GGA more efficiently than it reads GGU and GGC suggesting that the mispair C . A between the wobble position of the anticodon and the third codon position might have appreciable stability.

Amino Acid Sequence↗