Biomedical subjects

Dieter Oesterhelt

Publications and source records attributed to Dieter Oesterhelt.

39 records · Page 3Linked to original sources

PubMed2002

Discovery of two novel families of proteins that are proposed to interact with prokaryotic SMC proteins, and characterization of the Bacillus subtilis family members ScpA and ScpB.

Structural maintenance of chromosomes (SMC) proteins are present in all eukaryotes and in many prokaryotes. Eukaryotic SMC proteins form complexes with various non-SMC subunits, which affect their function, whereas the prokaryotic homologues had no known non-SMC partners and were thought to act as simple homodimers. Here we describe two novel families of proteins, widespread in archaea and (Gram-positive) bacteria, which we denote 'segregation and condensation proteins' (Scps). ScpA genes are localized next to smc genes in nearly all SMC- containing archaea, suggesting that they belong to the same operon and are thus involved in a common process in the cell. The function of ScpA was studied in Bacillus subtilis, which also harbours a well characterized smc gene. Here we show that scpA mutants display characteristic phenotypes nearly identical to those of smc mutants, including temperature- sensitive growth, production of anucleate cells, formation of aberrant nucleoids, and chromosome splitting by the so-called guillotine effect. Thus, both SMC and ScpA are required for chromosome segregation and condensation. Interestingly, mutants of another B. subtilis gene, scpB, which is localized downstream from scpA, display the same phenotypes, which indicate that ScpB is also involved in these functions. ScpB is generally present in species that also encode ScpA. The physical interaction of ScpA and SMC was proven (i) by the use of the yeast two-hybrid system and (ii) by the isolation of a complex containing both proteins from cell extracts of B. subtilis. By extension, we speculate that interaction of orthologues of the two proteins is important for chromosome segregation in many archaea and bacteria, and propose that SMC proteins generally have non-SMC protein partners that affect their function not only in eukaryotes but also in prokaryotes.

Amino Acid Sequence↗

PubMed2002

Role of the N- and C-terminal regions of the PufX protein in the structural organization of the photosynthetic core complex of Rhodobacter sphaeroides.

The core complex of Rhodobacter sphaeroides is formed by the association of the light-harvesting antenna 1 (LH1) and the reaction center (RC). The PufX protein is essential for photosynthetic growth; it is located within the core in a 1 : 1 stoichiometry with the RC. PufX is required for a fast ubiquinol exchange between the Q(B) site of the RC and the Qo site of the cytochrome bc1 complex. In vivo the LH1-PufX-RC complex is assembled in a dimeric form, where PufX is involved as a structural organizer. We have modified the PufX protein at the N and the C-terminus with progressive deletions. The nine mutants obtained have been characterized for their ability for photosynthetic growth, the insertion of PufX in the core LH1-RC complex, the stability of the dimers and the kinetics of flash-induced reduction of cytochrome b561 of the cytochrome bc1 complex. Deletion of 18 residues at the N-terminus destabilizes the dimer in vitro without preventing photosynthetic growth. The dimer (or a stable dimer) does not seem to be a necessary requisite for the photosynthetic phenotype. Partial C-terminal deletions impede the insertion of PufX, while the complete absence of the C-terminus leads to the insertion of a PufX protein composed of only its first 53 residues and does not affect the photosynthetic growth of the bacterium. Overall, the results point to a complex role of the N and C domains in the structural organization of the core complex; the N-terminus is suggested to be responsible mainly for dimerization, while the C-terminus is thought to be involved mainly in PufX assembly.

Amino Acid Sequence↗

PubMedDate not supplied

The crystal structure of the L1 intermediate of halorhodopsin at 1.9 angstroms resolution.

The mutant T203V of the light driven chloride pump halorhodopsin from Halobacterium salinarum was crystallized and the X-ray structure was solved at 1.6 angstroms resolution. The T203V structure turned out to be nearly identical to the wild type protein with a root mean square deviation of 0.43 angstroms for the carbon alpha atoms of the protein backbone. Two chloride binding (CB) sites were demonstrated by a substitution of chloride with bromide and an analysis of anomalous difference Fourier maps. The CB1 site was found at the same position as in the wild type structure. In addition, a second chloride binding site CB2 was identified around Q105 due to higher resolution in the mutant crystal. As T203V showed a 10 times slower decay of its photocycle intermediate L, this intermediate could be trapped with an occupancy of 60% upon illumination at room temperature and subsequent cooling to 120 degrees K. Fourier transform infrared spectroscopy clearly identified the crystal to be trapped in the L1 intermediate state and the X-ray structure was solved to 1.9 angstroms resolution. In this intermediate, the chloride moved by 0.3 angstroms within binding site CB1 as indicated by peaks in difference Fourier density maps. The chloride in the second binding site CB2 remained unchanged. Thus, intraproteinous chloride translocation from the extracellular to the cytoplasmic part of the protein must occur in reaction steps following the L1 intermediate in the catalytic cycle of halorhodopsin.

Amino Acid Substitution↗