Kishiko Nikaido

Crystal structure of the ATP-binding subunit of an ABC transporter.

ABC transporters (also known as traffic ATPases) form a large family of proteins responsible for the translocation of a variety ofcompounds across membranes of both prokaryotes and eukaryotes. The recently completed Escherichia coli genome sequence revealed that the largest family of paralogous E. coli proteins is composed of ABC transporters. Many eukaryotic proteins of medical significance belong to this family, such as the cystic fibrosis transmembrane conductance regulator (CFTR), the P-glycoprotein (or multidrug-resistance protein) and the heterodimeric transporter associated with antigen processing (Tap1–Tap2). Here we report the crystal structure at 1.5 Å resolution of HisP, the ATP-binding subunit of the histidine permease, which is an ABC transporter from Salmonella typhimurium. We correlate the details of this structure with the biochemical, genetic and biophysical properties of the wild-type and several mutant HisP proteins. The structure provides a basis for understanding properties of ABC transporters and of defective CFTR proteins.

Purification and Characterization of HisP, the ATP-binding Subunit of a Traffic ATPase (ABC Transporter), the Histidine Permease of Salmonella typhimurium SOLUBILITY, DIMERIZATION, AND ATPase ACTIVITY

The nucleotide-binding subunit, HisP, of the histidine permease, a traffic ATPase (ABC transporter), has been purified as a soluble protein and characterized. Addition of a 6-histidine extension (HisP(His6)) allows a rapid and effective metal affinity purification, giving a 30-fold purification with a yield of 50%. HisP(his6) is indistinguishable from underivatized HisP when incorporated into the permease membrane-bound complex, HisQMP2. Purified HisP(his6) has a strong tendency to precipitate; 5 mm ATP and 20% glycerol maintain it in solution at a high protein concentration. HisP(his6) is active as a dimer, binds ATP with aK d value of 205 μm, and hydrolyzes it at a rate comparable to that of HisQMP2; in contrast to the latter, it does not display cooperativity for ATP. HisP(his6) has been characterized with respect to substrate and inhibitor specificity and various physico-chemical characteristics. Its pH optimum is 7 and it requires a cation for activity, with Co2+ and Mn2+ being more effective than Mg2+ at lower concentrations but inhibitory in the higher concentration range. In contrast to the intact complex, HisP(his6) is not inhibited by vanadate but is inhibited byN-ethylmaleimide. Neither the soluble receptor, HisJ, nor the transport substrate, histidine, has any effect on the activity.

One Intact ATP-binding Subunit Is Sufficient to Support ATP Hydrolysis and Translocation in an ABC Transporter, the Histidine Permease

The membrane-bound complex of theSalmonella typhimurium histidine permease, a member of the ABC transporters (or traffic ATPases) superfamily, is composed of two integral membrane proteins, HisQ and HisM, and two copies of an ATP-binding subunit, HisP, which hydrolyze ATP, thus supplying the energy for translocation. The three-dimensional structure of HisP has been resolved. Extensive evidence indicates that the HisP subunits form a dimer. We investigated the mechanism of action of such a dimer, both within the complex and in soluble form, by creating heterodimers between the wild type and mutant HisP proteins. The data strongly suggest that within the complex both subunits hydrolyze ATP and that one subunit is activated by the other. In a heterodimer containing one wild type and one hydrolysis defective subunit both hydrolysis and ligand translocation occur at half the rate of the wild type. Soluble HisP also hydrolyzes ATP if one subunit is inactive; its specific activity is identical to that of the wild type, indicating that only one of the subunits in a soluble dimer is involved in hydrolysis. We show that the activating ability varies depending on the nature of the substitution of a well conserved residue, His-211.

Nitrogen regulation in Salmonella typhimurium. Identification of an ntrC protein-binding site and definition of a consensus binding sequence.

We have investigated the DNA‐binding ability of a nitrogen regulatory protein, the product of the ntrC gene, to several nitrogen‐regulated promoters in Salmonella typhimurium. The ntrC protein is able to bind to the regulatory region (dhuA) of an operon coding for genes involved in the active transport of histidine, but not to another transport‐related regulatory region, argTr. It bound to two different sites within the regulatory region of glnA (glutamine synthetase) and to one site in the regulatory region for the ntrBC operon. A consensus sequence has been derived from these four binding sites. The binding sequence displays dyad symmetry, as expected for the dimeric ntrC protein. The relationship of the binding sites to regulation of transcription initiation and termination, and to published homologies within the sequences of regulatory sites for nif genes is discussed.

Purification and Characterization of the Membrane-Bound Complex of an ABC Transporter, the Histidine Permease

The bacterial histidine permease, an ABC transporter, from Salmonella typhimurium is composed of a membrane-bound complex, HisQMP2, comprising two hydrophobic subunits (HisQ and HisM), two copies of an ATP-hydrolyzing subunit, HisP, and a soluble receptor, HisJ. We describe the purification and characterization of HisQMP2 using a 6-histidines extension at the carboxy terminus of HisP [HisQMP2(his6)]. The purification is rapid and effective, giving a seven–fold purification with a yield of 85 and 98% purity. Two procedures are described differing in the detergent used (decanoylsucrose and octylglucoside, respectively) and in the presence of phospholipid. HisQMP2(his6) has ATPase and transport activities upon reconstitution into proteoliposomes (PLS). HisQMP2(his6) has a low level ATPase activity (intrinsic activity), which is stimulated to a different extent by the receptor—liganded and unliganded. Its pH optimum is 7.8–8.0, it requires a cation for activity and it displays cooperativity for ATP. The effect of various ATP analogs was analyzed. Determination of the molecular size of HisQMP2(his6) indicates that it is a monomer. The permeability properties of two kinds of reconstituted PLS preparations are described.

Regulation of a transport operon promoter in Salmonella typhimurium: identification of sites essential for nitrogen regulation.

SummaryThe promoter of nitrogen-regulated transport, argTr, has been mutationally altered in order to determine the features that are essential for its response to nitrogen availability. Deletions of all sequences upstream of position-44 or downstream of position +2 had no effect no nitrogen regulation of argTr. These deletions define a small region of 44 bp where all necessary features for nitrogen regulation are located. This region includes for nitrogen regulation are located. This region includes sequences highly homologous to the nif consensus promoter. Alteration of this particular sequence caused drastic changes in the response to changes of nitrogen availability, thus indicating that they are directly involved in regulation. This implies that the NtrC protein must also act within this small region of the promoter. The data are discussed in terms of current-hypotheses concerning nitrogen regulation. In addition, we have shown 1. that carbon regulation at this promoter must occur at a site upstream from the nitrogen promoter; 2. that nifA can replace ntrC in the regulation of argTr.

Crystallization and preliminary X-ray studies of HisJ and LAO periplasmic proteins from Salmonella typhimurium☆

Two periplasmic binding proteins, HisJ and LAO, which are involved in histidine and arginine transport, respectively, have been crystallized. Preliminary X-ray diffraction studies of the HisJ and LAO crystals show that both belong to the orthorhombic space group P2(1)2(1)2(1) and have unit cell dimensions of a = 39.26 A, b = 66.17 A, c = 88.33 A and a = 36.08 A, b = 78.34 A, c = 102.02 A, respectively. Both HisJ and LAO crystals diffract beyond 2.0 A resolution.

Overproduction of the membrane-bound components of the histidine permease from Salmonella typhimurium: Identification of the M protein

The periplasmic histidine permease of Salmonella typhimurium is composed of a soluble histidine-binding protein and three membrane-bound components. These latter are produced in very small amounts and only two, the Q and the P protein, have been previously identified. This paper describes the construction of a plasmid carrying the hisQ, hisM, and hisP genes under the control of the lambda PL promoter, thus allowing great overproduction of those gene products. The M protein has been identified in such overproducing strains and its nature confirmed by constructing in vitro hisM deletions within the plasmid. With these results the identification of all components of the histidine permease has been completed.