Affiliation:
1. Department of Biochemistry, Chicago College of Osteopathic Medicine, Midwestern University, 555 31st Street, Downers Grove, Illinois 60515
Abstract
ABSTRACT
Escherichia coli
AbgT was first identified as a structural protein enabling the growth of
p
-aminobenzoate auxotrophs on exogenous
p
-aminobenzoyl-glutamate (M. J. Hussein, J. M. Green, and B. P. Nichols, J. Bacteriol. 180:6260-6268, 1998). The
abg
region includes
abgA
,
abgB
,
abgT
, and
ogt
; these genes may be regulated by AbgR, a divergently transcribed LysR-type protein. Wild-type cells transformed with a high-copy-number plasmid encoding
abgT
demonstrate saturable uptake of
p
-aminobenzoyl-glutamate (
K
T
= 123 μM); control cells expressing vector demonstrate negligible uptake. The addition of metabolic poisons inhibited uptake of
p
-aminobenzoyl-glutamate, consistent with this process requiring energy.
p-
Aminobenzoyl-glutamate taken in by cells expressing large amounts of AbgT alone is not rapidly metabolized to a form that is trapped in the cell, as the addition of nonradioactive
p-
aminobenzoyl-glutamate to these cells results in a rapid loss of intracellular label. The addition of nonradioactive
p
-aminobenzoate has no effect. The
abgA
,
abgB
, and
abgAB
genes were cloned into the medium-copy-number plasmid pACYC184;
p
-aminobenzoate auxotrophs transformed with the clone encoding
abgAB
demonstrated enhanced ability to grow on low levels of
p
-aminobenzoyl-glutamate. When transformed with complementary plasmids encoding high-copy levels of
abgT
and medium-copy levels of
abgAB
,
p
-aminobenzoate auxotrophs grew on 50 nM
p
-aminobenzoyl-glutamate. Our data are consistent with a model of
p
-aminobenzoyl-glutamate utilization in which AbgT catalyzes transport of
p
-aminobenzoyl-glutamate, followed by cleavage to
p
-aminobenzoate by a protein composed of subunits encoded by
abgA
and
abgB.
While endogenous expression of these genes is very low under the conditions in which we performed our experiments, these genes may be induced by AbgR bound to an unknown molecule. The true physiological role of this region may be related to some molecule similar to
p
-aminobenzoyl-glutamate, such as a dipeptide.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
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