Structures of the multidrug exporter AcrB reveal a proximal multisite drug-binding pocket

AcrB and its homologues are the principal multidrug transporters in Gram-negative bacteria and are important in antibiotic drug tolerance. AcrB is a homotrimer that acts as a tripartite complex with the outer membrane channel TolC and the membrane fusion protein AcrA. Minocycline and doxorubicin have been shown to bind to the phenylalanine cluster region of the binding monomer. Here we report the crystal structures of AcrB bound to the high-molecular-mass drugs rifampicin and erythromycin. These drugs bind to the access monomer, and the binding sites are located in the proximal multisite binding pocket, which is separated from the phenylalanine cluster region (distal pocket) by the Phe-617 loop. Our structures indicate that there are two discrete multisite binding pockets along the intramolecular channel. High-molecular-mass drugs first bind to the proximal pocket in the access state and are then forced into the distal pocket in the binding state by a peristaltic mechanism involving subdomain movements that include a shift of the Phe-617 loop. By contrast, low-molecular-mass drugs, such as minocycline and doxorubicin, travel through the proximal pocket without specific binding and immediately bind to the distal pocket. The presence of two discrete, high-volume multisite binding pockets contributes to the remarkably broad substrate recognition of AcrB.     

CXorf6 is a causative gene for hypospadias

46,XY disorders of sex development (DSD) refer to a wide range of abnormal genitalia, including hypospadias, which affects approximately 0.5% of male newborns. We identified three different nonsense mutations of CXorf6 in individuals with hypospadias and found that its mouse homolog was specifically expressed in fetal Sertoli and Leydig cells around the critical period for sex development. These data imply that CXorf6 is a causative gene for hypospadias.     

Fluctuation and response in biology

In 1905, Albert Einstein proposed that the forces that cause the random Brownian motion of a particle also underlie the resistance to macroscopic motion when a force is applied. This insight, of a coupling between fluctuation (stochastic behavior) and responsiveness (non-stochastic behavior), founded an important branch of physics. Here we argue that his insight may also be relevant for understanding evolved biological systems, and we present a ‘fluctuation–response relationship’ for biology. The relationship is consistent with the idea that biological systems are similarly canalized to stochastic, environmental, and genetic perturbations. It is also supported by in silico evolution experiments, and by the observation that ‘noisy’ gene expression is often both more responsive and more ‘evolvable’. More generally, we argue that in biology there is (and always has been) an important role for macroscopic theory that considers the general behavior of systems without concern for their intimate molecular details.     

Insulin-like effect of dichloroacetic acid on hexose transport in Swiss 3T3 cells

Summary Hexose transport in Swiss 3T3 cells was increased by treatment with dichloroacetic acid as well as by treatment with insulin. Neither extra-nor intracellular Ca²⁺ was found to be involved in their stimulatory action. On the other hand, the removal of intracellular Mg²⁺ resulted in a loss of the stimulation. These results suggest that dichloroacetic acid stimulates the hexose transport in Mg²⁺-dependent manner, similar to that of insulin.This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Science and Culture, and the Ministry of Health and Welfare of Japan.     

Chiral influence of sex pheromonal substances on responses of the male American cockroach

Summary In order to elucidate the roles of optical enantiomers of sex pheromonal substances of the American cockroach, behavioral assays with a single enantiomer and with mixtures of enantiomers of sex pheromone mimics were carried out. Inactive enantiomers [(–)-enantiomers] had no influence on the potency of enantiomers active as sex pheromones [(+)-enantiomers]. By analysis of the results from EAG recordings with single and mixed sample of the enantiomers, it was confirmed that (–)-enantiomers did not react with the sex pheromone receptors which are responsive to (+)-enantiomers.We acknowledge technical assistance from Miss R. Kimura.     

A record of Permian subaqueous vent activity in southeastern Brazil

The remarkable occurrence of more than 4,500 conical siliceous mounds in an area of less than 1.5 square kilometres has been reported in the Paraná basin, near Anhembi, S?o Paulo, in southeastern Brazil. These structures, which are up to two metres high, are thought to have been formed at the margin of a very shallow, broad but waning internal sea, and it was originally suggested that they are stromatolites. Yet their restricted occurrence, unusual abundance and nearly pure siliceous composition have never been satisfactorily explained by this hypothesis. Here we report field and laboratory observations on their shape, construction, composition and mineralogy. On the basis of our data we suggest that the conical mounds are the result of subaqueous Late Permian vent activity in southwestern Gondwana. The present siliceous cone field differs considerably from other Palaeozoic siliceous hot spring deposits, such as those at Rhynie, Scotland, and the Drummond basin, Australia, and therefore represents an unusual occurrence of vent activity.     

Possible involvement of protein kinase C in the stimulation of amino acid transport by phorbol ester,platelet-derived growth factor and A23187 in Swiss 3T3 cells

Summary Stimulation of amino acid transport induced by phorbol-12, 13-dibutyrate, platelet-derived growth factor or A23187 was not observed in cells lacking protein kinase C. On the other hand, stimulation of transport by epidermal growth factor or insulin was not affected. These results suggested that the stimulation of amino acid transport is mediated by at least two separate pathways.This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Science and Culture, and the Ministry of Health and Welfare of Japan.     

Possible involvement of protein kinase C in the stimulation of amino acid transport by phorbol ester, platelet-derived growth factor and A23187 in Swiss 3T3 cells

Stimulation of amino acid transport induced by phorbol-12,13-dibutyrate, platelet-derived growth factor or A23187 was not observed in cells lacking protein kinase C. On the other hand, stimulation of transport by epidermal growth factor or insulin was not affected. These results suggested that the stimulation of amino acid transport is mediated by at least two separate pathways.