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J. Bacteriol., 06 1997, 3697-3705, Vol 179, No. 11
L Tang, AC Weissborn and EP Kennedy
Acyl carrier protein participates in a number of biosynthetic pathways in
Escherichia coli: fatty acid biosynthesis, phospholipid biosynthesis,
lipopolysaccharide biosynthesis, activation of prohemolysin, and
membrane-derived oligosaccharide biosynthesis. The first four pathways
require the protein's prosthetic group, phosphopantetheine, to assemble an
acyl chain or to transfer an acyl group from the thioester linkage to a
specific substrate. By contrast, the phosphopantetheine prosthetic group is
not required for membrane- derived oligosaccharide biosynthesis, and the
function of acyl carrier protein in this biosynthetic scheme is currently
unknown. We have combined biochemical and molecular biological approaches
to investigate domains of acyl carrier protein that are important for
membrane-derived oligosaccharide biosynthesis. Proteolytic removal of the
first 6 amino acids from acyl carrier protein or chemical synthesis of a
partial peptide encompassing residues 26 to 50 resulted in losses of
secondary and tertiary structure and consequent loss of activity in the
membrane glucosyltransferase reaction of membrane-derived oligosaccharide
biosynthesis. These peptide fragments, however, inhibited the action of
intact acyl carrier protein in the enzymatic reaction. This suggests a role
for the loop regions of the E. coli acyl carrier protein and the need for
at least two regions of the protein for participation in the
glucosyltransferase reaction. We have purified acyl carrier protein from
eight species of Proteobacteria (including representatives from all four
subgroups) and characterized the proteins as active or inhibitory in the
membrane glucosyltransferase reaction. The complete or partial amino acid
sequences of these acyl carrier proteins were determined. The results of
site-directed mutagenesis to change amino acids conserved in active, and
altered in inactive, acyl carrier proteins suggest the importance of
residues Glu-4, Gln-14, Glu-21, and Asp-51. The first 3 of these residues
define a face of acyl carrier protein that includes the beginning of the
loop region, residues 16 to 36. Additionally, screening for membrane
glucosyltransferase activity in membranes from bacterial species that had
acyl carrier proteins that were active with E. coli membranes revealed the
presence of glucosyltransferase activity only in the species most closely
related to E. coli. Thus, it seems likely that only bacteria from the
Proteobacteria subgroup gamma-3 have periplasmic glucans synthesized by the
mechanism found in E. coli.
Copyright © 1997, American Society for Microbiology
Domains of Escherichia coli acyl carrier protein important for membrane- derived-oligosaccharide biosynthesis
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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