An ongoing public health challenge is to develop vaccines that are effective against infectious diseases that have global relevance. Vaccines against serotypes of group B Streptococcus (GBS) that are prevalent in the United States and Europe are not optimally efficacious against serotypes common to other parts of the world. New technologies and innovative approaches are being used to identify GBS antigens that overcome serotype-specificity and that could form the basis of a globally effective vaccine against this opportunistic pathogen. This Review highlights efforts towards this goal and describes a template that can be followed to develop vaccines against other bacterial pathogens.

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Because pure cultures and a stable transformation system are not available for arbuscular mycorrhizal fungi, the role of their phosphate transporters for the symbiotic interaction with the plant up till now could not be studied. Here we report the cloning and the functional analysis of a gene encoding a phosphate transporter (PiPT) from the root endophytic fungus Piriformospora indica, which can be grown axenically. The PiPT polypeptide belongs to the major facilitator superfamily. Homology modeling reveals that PiPT exhibits twelve transmembrane helices divided into two halves connected by a large hydrophilic loop in the middle. The function of the protein encoded by PiPT was confirmed by complementation of a yeast phosphate transporter mutant. The kinetic analysis of PiPT (K m 25 M) reveals that it belongs to the high affinity phosphate transporter family (Pht1). Expression of PiPT was localized to the external hyphae of P. indica colonized with maize plant root, which suggests that external hyphae are the initial site of phosphate uptake from the soil. To understand the physiological role of PiPT, knockdown transformants of the gene were prepared using electroporation and RNA interference. Knockdown transformants transported a significantly lower amount of phosphate to the host plant than wild-type P. indica. Higher amounts of phosphate were found in plants colonized with wild-type P. indica than that of non-colonized and plants colonized with knockdown PiPT P. indica. These observations suggest that PiPT is actively involved in the phosphate transportation and, in turn, P. indica helps improve the nutritional status of the host plant.

Here we describe the X-ray crystal structure of a double-Trp mutant (Gly46→Trp/Gly262→Trp) of the lactose permease of Escherichia coli (LacY) with a bound, high-affinity lactose analog. Although thought to be arrested in an open-outward conformation, the structure is almost occluded and is partially open to the periplasmic side; the cytoplasmic side is tightly sealed. Surprisingly, the opening on the periplasmic side is sufficiently narrow that sugar cannot get in or out of the binding site. Clearly defined density for a bound sugar is observed at the apex of the almost occluded cavity in the middle of the protein, and the side chains shown to ligate the galactopyranoside strongly confirm more than two decades of biochemical and spectroscopic findings. Comparison of the current structure with a previous structure of LacY with a covalently bound inactivator suggests that the galactopyranoside must be fully ligated to induce an occluded conformation. We conclude that protonated LacY binds D-galactopyranosides specifically, inducing an occluded state that can open to either side of the membrane.T he lactose permease of Escherichia coli (LacY), a paradigm for the major facilitator superfamily (MFS), binds and catalyzes transport of D-galactose and D-galactopyranosides specifically with an H + (1, 2). In contrast, LacY does not recognize D-glucose or D-glucopyranosides, which differ only in the orientation of the C4-OH of the pyranosyl ring. By using the free energy released from the energetically downhill movement of H + in response to the electrochemical H + gradient (Δμ H +), LacY catalyzes the uphill (active) transport of galactosides against a concentration gradient. Because coupling between sugar and H + translocation is obligatory, in the absence of Δμ H +, LacY also can transduce the energy released from the downhill transport of sugar to drive uphill H + transport with the generation of Δμ H +, the polarity of which depends upon the direction of the sugar gradient.It also has been shown that LacY binds sugar with a pK a of ∼10.5 and that sugar binding does not induce a change in ambient pH; both findings indicate that the protein is protonated over the physiological range of pH (3-5). These observations and many others (1, 2) provide evidence for an ordered kinetic mechanism in which protonation precedes galactoside binding on one side of the membrane and follows sugar dissociation on the other side. Recent considerations (6) suggest that a similar ordered mechanism may be common to other members of the MFS.Because equilibrium exchange and counterflow are unaffected by imposition of Δμ H +, it is apparent that the alternating accessibility of sugar-and H + -binding sites to either side of the membrane is the result of sugar binding and dissociation and not of Δμ H + (reviewed in refs. 1 and 2). Moreover, downhill lactose/ H + symport from a high to a low lactose concentration exhibits a primary deuterium isotope effect that is not observed for Δμ H +-driven lactose/H + symport, equilibrium exchange, or count...