ABSTRACT
The sgaTBA genes of Escherichia coli encode a putative 12-transmembrane α-helical segment (12 TMS) transporter, an enzyme IIB-like protein and an enzyme IIA-like protein of the phosphotransferase system (PTS), respectively. We show that all three proteins as well as the energy-coupling PTS proteins, enzyme I and HPr, are required for the anaerobic utilization and uptake of l-ascorbate in vivo and its phosphoenolpyruvate-dependent phosphorylation in vitro. The transporter exhibits an apparent Km
for l-ascorbate of 9 μM and is highly specific. The sgaTBA genes are regulated at the transcriptional level by the yjfQ gene product, as well as by Crp and Fnr. The yjfR gene product is essential for l-ascorbate utilization and probably encodes a cytoplasmic l-ascorbate 6-phosphate lactonase. We conclude that SgaT represents a novel prototypical enzyme IIC that functions with SgaA and SgaB to allow phosphoryl transfer from HPr(his-P) to l-ascorbate via the phosphoryl transfer pathway: PEP → enzyme I-P → HPr-P → IIA-
\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\stackrel{\mathrm{SgaA}}{\mathrm{P}}\) \end{document}
→ IIB-
\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\stackrel{\mathrm{SgaB}}{\mathrm{P}}\) \end{document}
\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\stackrel{\textstyle{\mathrm{IIC^{SgaT}}}}{{\rightarrow}}\) \end{document}
l-ascorbate-6-P.
Escherichia coli phosphoenolpyruvate dependent phosphotransferase system. NMR studies of the conformation of HPr and P-HPr and the mechanism of energy coupling
