Copper resistance determinants in bacteria.

Copper is an essential trace element that is utilized in a number of oxygenases and electron transport proteins, but it is also a highly toxic heavy metal, against which all organisms must protect themselves. Known bacterial determinants of copper resistance are plasmid-encoded. The mechanisms which confer resistance must be integrated with the normal metabolism of copper. Different bacteria have adopted diverse strategies for copper resistance, and this review outlines what is known about bacterial copper resistance mechanisms and their genetic regulation.     

The aacA-aphD gentamicin and kanamycin resistance determinant of Tn4001 from Staphylococcus aureus: expression and nucleotide sequence analysis

The aacA-aphD aminoglycoside resistance determinant of the Staphylococcus aureus transposon Tn4001, which specifies resistance to gentamicin, tobramycin and kanamycin, has been cloned and shown to express these resistances in Escherichia coli. The determinant encoded a single protein with an apparent size of 59 kDa which specified both aminoglycoside acetyltransferase [AAC(6')] and aminoglycoside phosphotransferase [APH(2")] activities. Nucleotide sequence analysis of the determinant showed it to be capable of encoding a 479-amino-acid protein of 56.9 kDa. analysis of Tn1725 insertion mutants of the determinant indicated that resistance to tobramycin and kanamycin is due to the AAC activity specified by, approximately, the first 170 amino acids of the predicted protein sequence and is consistent with the gentamicin resistance, specified by the APH activity, being encoded within the C-terminal region of the protein. Comparison of the C-terminal end of the predicted amino acid sequence with the reported sequences of 13 APHs and a viomycin phosphotransferase revealed a region which is highly conserved among these phosphotransferases.     

Membrane transport proteins: implications of sequence comparisons.

Analyses of the sequences and structures of many transport proteins that differ in substrate specificity, direction of transport and mechanism of transport suggest that they form a family of related proteins. Their sequence similarities imply a common mechanism of action. This hypothesis provides an objective basis for examining their mechanisms of action and relationships to other transporters.     

Nucleotide sequence analysis of IS256 from the Staphylococcus aureus gentamicin-tobramycin-kanamycin-resistance transposon Tn4001

Resistance to the aminoglycosides gentamicin, tobramycin and kanamycin (GmTmKmR) in Australian clinical strains of Staphylococcus aureus is commonly carried on the composite transposon Tn4001. The resistance gene aacA-aphD of Tn4001, which encodes a bifunctional AAC(6')-APH(2") modifying enzyme, is flanked by two 1324-bp inverted repeats, IS256L and IS256R, that are identical in sequence. Analysis of the IS256 sequence revealed structural features characteristic of IS elements including 26-bp imperfect terminal inverted repeats and a single open reading frame with coding capacity for a 45.6 kDa protein. The nucleotide sequence of IS256 described here, together with the sequence of the aacA-aphD gene reported previously [Rouch et al., J. Gen. Microbiol. 133 (1987) 3039-3052], completes the entire sequence of Tn4001, which totals 4566 bp.     

IS257 from Staphylococcus aureus: member of an insertion sequence superfamily prevalent among gram-positive and gram-negative bacteria

The nucleotide sequences for the IS257 family of insertion sequences from Staphylococcus aureus were compared with those of the ISS1 family from Streptococcus lactis and the IS15 family which is widespread amongst Gram-negative bacteria. These elements have a striking degree of similarity in both their putative transposase polypeptide sequences and their nucleotide sequences (40 to 64% between pairs), including 12 out of 14 bp conservation in their terminal inverted repeats. The evolutionary distance between the IS15 family and the IS257 and ISS1 families of Gram-positive origin is approximately twice that between the IS257 and ISS1 families. Analysis of base substitutions in the three sequences has provided insights into the effect of selection for the G + C content of immigrant genes to conform to that of their hosts, and into the evolution of biases in overall amino acid composition of cellular proteins in prokaryotes and eukaryotes. The IS257, ISS1, IS15 families form a superfamily of insertion sequences that has been involved in the spread of a number of antimicrobial resistance determinants in Gram-positive and Gram-negative pathogens.     

The Chlamydia trachomatis Mip-like protein is a lipoprotein.

The Mip-like protein of Chlamydia trachomatis is similar to the Mip protein of Legionella pneumophila and may be equally important for the initiation of intracellular infection. This article presents data which identify the chlamydial Mip-like protein as a lipoprotein. The amino acid sequence of the Mip-like protein contains a signal peptidase II recognition sequence, as is seen in procaryotic lipoproteins. Palmitic acid was incorporated into the recombinant chlamydial Mip-like protein. Globomycin, known to inhibit signal peptidase II, inhibited processing of the recombinant Mip-like protein. Labelling of chlamydial organisms with palmitic acid revealed incorporation into the native Mip-like protein.