PcaK, a high-affinity permease for the aromatic compounds 4-hydroxybenzoate and protocatechuate from Pseudomonas putida

J Bacteriol. 1997 Aug;179(16):5056-61. doi: 10.1128/jb.179.16.5056-5061.1997.


PcaK is a transporter and chemoreceptor protein from Pseudomonas putida that is encoded as part of the beta-ketoadipate pathway regulon for aromatic acid degradation. When expressed in Escherichia coli, PcaK was localized to the membrane and catalyzed the accumulation of two aromatic substrates, 4-hydroxybenzoate and protocatechuate, against a concentration gradient. Benzoate inhibited 4-hydroxybenzoate uptake but was not a substrate for PcaK-catalyzed transport. A P. putida pcaK mutant was defective in its ability to accumulate micromolar amounts of 4-hydroxybenzoate and protocatechuate. The mutant was also impaired in growth on millimolar concentrations of these aromatic acids. In contrast, the pcaK mutant grew at wild-type rates on benzoate. The Vmax for uptake of 4-hydroxybenzoate was at least 25 nmol/min/mg of protein, and the Km was 6 microM. PcaK-mediated transport is energized by the proton motive force. These results show that although aromatic acids in the undissociated (uncharged) form can diffuse across bacterial membranes, high-specificity active transport systems probably also contribute to the ability of bacteria to grow on the micromolar concentrations of these compounds that are typically present in soil. A variety of aromatic molecules, including naturally occurring lignin derivatives and xenobiotics, are metabolized by bacteria and may be substrates for transport proteins. The characterization of PcaK provides a foundation for understanding active transport as a critical step in the metabolism of aromatic carbon sources.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Benzoates / metabolism
  • Benzoic Acid
  • Biological Transport, Active
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Hydrogen-Ion Concentration
  • Hydroxybenzoates / metabolism*
  • Kinetics
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism*
  • Mutation
  • Parabens / metabolism*
  • Proton-Motive Force
  • Pseudomonas putida / enzymology
  • Pseudomonas putida / growth & development
  • Pseudomonas putida / metabolism*


  • Bacterial Proteins
  • Benzoates
  • Carrier Proteins
  • Hydroxybenzoates
  • Membrane Transport Proteins
  • Parabens
  • PcaK protein, Pseudomonas
  • protocatechuic acid
  • Benzoic Acid
  • 4-hydroxybenzoic acid