Fe(III) binding to Bacillus PS3 F(1)ATPase, alphabeta subcomplexes and isolated alpha- and beta-subunits

Isolated alpha- and beta-subunits of Thermophilic Bacillus PS3 F(1)ATPase (TF(1)) bind about 1 Fe(III) equivalent. Upon reassembling in the symmetric alpha(3)beta(3) hexamer, Fe(III) binding capacity decreases, as this complex binds about three Fe(III) equivalents. In accordance, when the hexamer is dissociated in the alpha(1)beta(1) heterodimer, each heterodimer binds about one Fe(III) equivalent. On the contrary, native TF(1) exhibits a single Fe(III) site. CD spectra in far UV indicate that upon Fe(III) binding both the whole complex and the isolated beta-subunit undergo structural modifications accompanied by decrease of alpha-helix content, while alpha-subunit doesn't. As in alpha(3)beta(3) and in the whole enzyme the number of bound Fe(III) equivalents is consistent with the number of beta-subunits in the "empty" conformation, it is inferred that the single Fe(III) site in TF(1) is probably located in beta(E).

Dynamics of iron uptake and Fe3O4 biomineralization during aerobic and microaerobic growth of Magnetospirillum gryphiswaldense

Iron uptake and magnetite (Fe3O4) crystal formation could be studied in the microaerophilic magnetic bacterium Magnetospirillum gryphiswaldense by using a radioactive tracer method for iron transport and a differential light-scattering technique for magnetism. Magnetite formation occurred only in a narrow range of low oxygen concentration, i.e., 2 to 7 microM O2 at 30 degrees C. Magnetic cells stored up to 2% iron as magnetite crystals in intracytoplasmic vesicles. This extraordinary uptake of iron was coupled tightly to the biomineralization of up to 60 magnetite crystals with diameters of 42 to 45 nm.

Iron-limited growth and kinetics of iron uptake in Magnetospirillum gryphiswaldense

Growth and magnetite formation in Magnetospirillum gryphiswaldense MSR-1 were found close to the maximum at an extracellular iron concentration of 15-20 microM. Ferrous iron was incorporated by a slow, diffusion-like process. Several iron chelators including various microbial siderophores were unable to promote transport of iron into the cells. In contrast, spent culture fluids stimulated the uptake of ferric iron in iron-depleted cells at a high rate, whereas fresh medium and transport buffer were unable to promote iron uptake. However, no siderophore-like compound could be detected in spent culture fluids by the Chrome Azurol S assay. Ferric iron uptake followed Michaelis-Menten kinetics with a Km of 3 microM and a Vmax of 0.86 nmol min-1 (mg dry weight)-1, suggesting a comparatively low-affinity, but high-velocity transport system. Iron incorporation was sensitive to 2,4-dinitrophenol and carbonylcyanide-m-chlorophenylhydrazone, indicating an energy-dependent transport process.

Conserved machinery of the bacterial flagellar motor

Novel periplasmic and cytoplasmic structural modules of the bases of bacterial flagella have been observed in situ and isolated using new biochemical protocols. Flagellar rotation may depend upon interactions of these modules with the intramembrane particle rings, a ubiquitous feature of flagellar bases necessary for torque generation. The outer membrane-associated basal disk of the Wolinella succinogenes polar flagellum has architecture well suited for interaction with the ring particles. However, antibody against the main W. succinogenes basal disk protein did not cross-react with flagella-enriched fractions from Salmonella typhimurium and Bacillus firmus; nor have such structures been observed in these species thus far. Antibodies against two S. typhimurium proteins, FliG and FliM, known to be involved in motor function and part of the cytoplasmic module in this species cross-reacted with flagella-enriched fractions from both W. succinogenes and B. firmus. In addition, flagellar cytoplasmic structure could be isolated from B. firmus. The basal disk may anchor the flagellar motor to the cell wall in some polar bacteria, but this does not seem to be a unique strategy. In contrast, the data indicate that the cytoplasmic module is conserved.

Nucleotide sequence of the Wolinella succinogenes flagellin, which contains in the antigenic domain two conserved regions also present in Campylobacter spp. and Helicobacter pylori

Wolinella succinogenes possesses one polar flagellum, which shows a characteristic surface pattern of parallel lines along the axis of the filament in electron microscopic images. We determined the gene sequence of the Wolinella flagellin, which is, as in most other bacteria, the only structural component of the filament. Sequence comparison with other members of the Proteobacteria revealed two highly conserved regions in the central part of the flagellin molecule among Campylobacter spp. and Helicobacter pylori, an area that had previously been described as highly variable. Similar surface patterns are found in related polarly flagellated bacteria, but not in Escherichia coli and Bacillus subtilis, which also lack these conserved regions.

The prokaryotic thermophilic TF1-ATPase is functionally compatible with the eukaryotic CFo-part of the chloroplast ATP-synthase

The ATP synthase from chloroplasts, CFo.F1, was reconstituted into liposomes, from which most of CF1 was removed by a short treatment with guanidinium chloride. ATP-dependent proton uptake was restored with these CFo-liposomes even better by the addition of the bacterial TF1-than of the related CF1-part. This proton uptake was prevented by tentoxin, a specific inhibitor of the CF1-ATPase, in these CFo.F1-liposomes, but not in the hybrid CFo.TF1-liposomes. Venturicidin, a specific inhibitor of proton flow through CFo, was able to block it in both the hybrid CFo.TF1-liposomes and reconstituted CFo.F1-liposomes. These results indicate that the bacterial TF1-part binds to the eukaryotic CFo-part of four subunits forming a functional CFo.TF1-ATPase.

An archimedian spiral: the basal disk of the Wolinella flagellar motor

The motor that powers the rotation of the bacterial flagellum reaches through both membranes into the cytoplasm of Gram-negative bacteria. The flagellum is connected by a flexible link (hook) to the motor axis, which passes through the center of a structure called the basal disk. The basal disk functions with the L-P ring complex as a bushing, enabling the rotation of the motor in the cell wall. The protein subunits of the basal disk of Wolinella succinogenes form an Archimedian spiral. The polymerization of subunits from a nucleation point at the motor in the form of a spiral allows constant growth of the basal disk. The disk is thought to provide a reinforcement at the flagellar insertion at the cell pole and to disperse forces that are generated by the momentum of the flagellar rotation.

Location of the basal disk and a ringlike cytoplasmic structure, two additional structures of the flagellar apparatus of Wolinella succinogenes

The basal body of Wolinella succinogenes consists of a central rod, a set of two rings (L and P rings), a basal disk from 70 to 200 nm in diameter, and a terminal knob. In negatively stained preparations of flagellar hook-basal body complexes, some disks remain fixed perpendicularly to the grid and show that such a disk is located on the distal side of the P ring. The basal disks have been isolated with and without the P ring; in both cases there is a hole in the center of the disk. The diameter of the disk is smaller in the presence of the P ring. The L-P ring complex is therefore assumed to be a bushing for the rod. Thin sections of whole bacteria and spheroplasts reveal that the disk is attached to the inner surface of the outer membrane. At the insertions of the flagellar hook-basal body-basal disk complexes, depressions are visible in negatively stained preparations of whole bacteria and spheroplasts. A new ringlike structure is connected to an elongation of the basal body into the cytoplasm in both preparations. Its diameter (60 nm) is larger than that of the M ring. A heavily stained compartment can be seen in between the new ringlike structure and the basal disk, which may be formed by the energy transducing units.

Basal-body-associated disks are additional structural elements of the flagellar apparatus isolated from Wolinella succinogenes

The intact flagella of Wolinella succinogenes, a gram-negative, anaerobic bacterium with a single polar flagellum, were obtained by an improved procedure, introduced recently by Aizawa et al. (S.-J. Aizawa, G. E. Dean, C. J. Jones, R. M. Macnab, and S. Yamaguchi, J. Bacteriol. 161:836-849, 1985) for the flagellum of Salmonella typhimurium. Disks with a diameter of 130 +/- 30 nm, which were attached to the basal body of the isolated intact flagella, could be identified by electron microscopy as additional structural elements of the bacterial flagellar apparatus. In freeze-dried and metal-shadowed samples, two rings of the basal body were detected on one side and a terminal knob was located on the other side of the disks. Suspension of the flagellar apparatus in acidic solution dissociated the flagellar filaments, yielding hook-basal body complexes with and without the associated disks. If whole cells were subjected to low pH, double disks of the same diameter and with a central hole of about 13 nm could be isolated. Similar parallel disks could be seen also in negatively stained whole cells. When uranyl acetate was used for negative staining of the intact flagella, concentric rings were detected on the disks, similar to the concentric membrane rings found by Coulton and Murray (J. W. Coulton and R. G. E. Murray, J. Bacteriol. 136:1037-1049, 1978) on platelike arrays of proteins in outer membrane preparations of Aquaspirillum serpens. Because the disks of W. succinogenes can be isolated together with the flagellar hook-basal body complex, they appear to be basal-body-rather than secondary membrane-associated structures. It is possible that these disks are the bearing or stator of this rotary device.

1H-NMR studies on nucleotide binding to the catalytic sites of bovine mitochondrial F1-ATPase

The conformation of adenine nucleotides bound to bovine mitochondrial F1-ATPase was investigated using transfer nuclear Overhauser enhancement measurements. It is shown that all nucleotides investigated adopt a predominantly anti conformation when bound to the catalytic sites. Furthermore, the experiment suggests that 8-azido-ADP and 8-azido-ATP, which are predominantly in the syn conformation in solution, are in the anti conformation when bound to F1 catalytic sites.