Mutation of a single residue, β-glutamate-20, alters protein–lipid interactions of light harvesting complex II

It is well established that assembly of the peripheral antenna complex, LH2, is required for proper photosynthetic membrane biogenesis in the purple bacterium Rhodobacter sphaeroides. The underlying interactions are, as yet, not understood. Here we examined the relationship between the morphology of the photosynthetic membrane and the lipid–protein interactions at the LH2–lipid interface. The non-bilayer lipid, phosphatidylethanolamine, is shown to be highly enriched in the boundary lipid phase of LH2. Sequence alignments indicate a putative lipid binding site, which includes β-glutamate-20 and the adjacent carotenoid end group. Replacement of β-glutamate-20 with alanine results in significant reduction of phosphatidylethanolamine and concomitant raise in phosphatidylcholine in the boundary lipid phase of LH2 without altering the lipid composition of the bulk phase. The morphology of the LH2 housing membrane is, however, unaffected by the amino acid replacement. In contrast, simultaneous modification of glutamate-20 and exchange of the carotenoid sphaeroidenone with neurosporene results in significant enlargement of the vesicular membrane invaginations. These findings suggest that the LH2 complex, specifically β-glutamate-20 and the carotenoids' polar head group, contribute to the shaping of the photosynthetic membrane by specific interactions with surrounding lipid molecules

ELECTRONIC AREA DETECTOR DATA REDUCTION SYSTEM AT THE SRS

With the current detector and computer technology, data collection at synchrotron x-radiation sources poses special problems. Fast data collection rates are essential for kinetic experiments at room temperatures. If maximum reflection measuring rates of 102-103 reflections per second for monochromatic and 105 reflections per second with white beam are to become feasible, some simplifications at data collection time must be made, at the expense of possible complications during data reduction at a later stage. The main benefit of EAD's over film is that a 3D profile scan of each reflection can maximise the peak-to-background ratio. The benefits are even more marked on synchrotron sources since the intrinsic mosaicity of protein crystals can be small. With optimum collimation the angular spread of a reflection can be reduced 5-fold over a conventional source, thus giving further improvement in signal-to-noise. Brief details are given of the EAD system (hardware and software) for protein crystallography at the SRS wiggler beam line, based on a TV system for 0.5 ≲ λ ≲ 1.5 Å

The three-dimensional structure of bovine odorant binding protein and its mechanism of odor recognition

Odorant binding protein (OBP) is the major odorant binding component of mammalian nasal mucosa. The two structures of bovine OBP reported in this paper (one crystallized as purified and one soaked in the presence of a selenium-containing odorant) show that: (i) the OBP dimer is composed of two compact domains related by an approximate two-fold axis of symmetry; (ii) between residues 122 and 123 the polypeptide chains cross from one domain to the other such that each domain is formed by residues from both monomers; (iii) purified OBP already contains two bound odorant molecules (one per monomer)—odorant binding occurs by replacement of these molecules with the added odorant; and (iv) the structure of the odorant binding site can explain OBP's extraordinarily broad odorant specificity