Identification of two intestinal vitamin D-dependent calcium-binding proteins in the X-linked hypophosphataemic mouse

Two vitamin D-dependent calcium binding proteins (CaBP) of molecular weight approximately 10,000 and 30,000 daltons have been identified in the intestinal mucosal cell cytosol of genetically hypophosphataemic (Hyp) male mice and their normal littermates. Similar amounts of vitamin D-dependent CaBP were found in the two groups of animals. The possible significance of this observation is discussed.     

A new florally dimorphic hexaploid, Echinocereus yavapaiensis sp. nov. (section Triglochidiatus, Cactaceae) from central Arizona

A florally dimorphic hexaploid (n=33), Echinocereus yavapaiensis M. A. Baker, is newly described and possesses the highest number of chromosomes known within the genus. Populations of E. yavapaiensis occur in central Arizona between 1025 and 1860 m elevation and are associated with volcanic bedrock. Fifty three percent of the individuals studied produce only pollen-sterile flowers, which fail to undergo meiosis within the microspore mother cells, while 47% develop only pollen-fertile flowers. Chromosome determinations are presented for 41 populations of Echinocereus, including E. arizonicus (n=11), E. canyonensis (n=22), E. coccineus (n=22), E. matudae (n=11), E. pacificus (n=22), E. mombergerianus (n=22), E. santaritensis (n=22), and E. yavapaiensis. A phenetic analysis compares morphological variability among populations of E. yavapaiensis to those of its closest allies.     

Mutations in Escherichia coli ExbB Transmembrane Domains Identify Scaffolding and Signal Transduction Functions and Exclude Participation in a Proton Pathway

The TonB system couples cytoplasmic membrane proton motive force (pmf) to active transport of diverse nutrients across the outer membrane. Current data suggest that cytoplasmic membrane proteins ExbB and ExbD harness pmf energy. Transmembrane domain (TMD) interactions between TonB and ExbD allow the ExbD C terminus to modulate conformational rearrangements of the periplasmic TonB C terminus in vivo. These conformational changes somehow allow energization of high-affinity TonB-gated transporters by direct interaction with TonB. While ExbB is essential for energy transduction, its role is not well understood. ExbB has N-terminus-out, C-terminus-in topology with three TMDs. TMDs 1 and 2 are punctuated by a cytoplasmic loop, with the C-terminal tail also occupying the cytoplasm. We tested the hypothesis that ExbB TMD residues play roles in proton translocation. Reassessment of TMD boundaries based on hydrophobic character and residue conservation among distantly related ExbB proteins brought earlier widely divergent predictions into congruence. All TMD residues with potentially function-specific side chains (Lys, Cys, Ser, Thr, Tyr, Glu, and Asn) and residues with probable structure-specific side chains (Trp, Gly, and Pro) were substituted with Ala and evaluated in multiple assays. While all three TMDs were essential, they had different roles: TMD1 was a region through which ExbB interacted with the TonB TMD. TMD2 and TMD3, the most conserved among the ExbB/TolQ/MotA/PomA family, played roles in signal transduction between cytoplasm and periplasm and the transition from ExbB homodimers to homotetramers. Consideration of combined data excludes ExbB TMD residues from direct participation in a proton pathway.