The three-dimensional structure of prostaglandin H2 synthase-1, an integral membrane protein, has been determined at 3.5 A resolution by X-ray crystallography. This bifunctional enzyme comprises three independent folding units: an epidermal growth factor domain, a membrane-binding motif and an enzymatic domain. Two adjacent but spatially distinct active sites were found for its haem-dependent peroxidase and cyclooxygenase activities. The cyclooxygenase active site is created by a long, hydrophobic channel that is the site of non-steroidal anti-inflammatory drug binding. The conformation of the membrane-binding motif strongly suggests that the enzyme integrates into only one leaflet of the lipid bilayer and is thus a monotopic membrane protein.

Photosystems I and II (PSI and II) are reaction centres that capture light energy in order to drive oxygenic photosynthesis; however, they can only do so by interacting with the multisubunit cytochrome b(6)f complex. This complex receives electrons from PSII and passes them to PSI, pumping protons across the membrane and powering the Q-cycle. Unlike the mitochondrial and bacterial homologue cytochrome bc(1), cytochrome b(6)f can switch to a cyclic mode of electron transfer around PSI using an unknown pathway. Here we present the X-ray structure at 3.1 A of cytochrome b(6)f from the alga Chlamydomonas reinhardtii. The structure bears similarities to cytochrome bc(1) but also exhibits some unique features, such as binding chlorophyll, beta-carotene and an unexpected haem sharing a quinone site. This haem is atypical as it is covalently bound by one thioether linkage and has no axial amino acid ligand. This haem may be the missing link in oxygenic photosynthesis.

The understanding of integral membrane protein (IMP) structure and function is hampered by the difficulty of handling these proteins. Aqueous solubilization, necessary for many types of biophysical analysis, generally requires a detergent to shield the large lipophilic surfaces displayed by native IMPs. Many proteins remain difficult to study owing to a lack of suitable detergents. We introduce a class of amphiphiles, each of which is built around a central quaternary carbon atom derived from neopentyl glycol, with hydrophilic groups derived from maltose. Representatives of this maltose-neopentyl glycol (MNG) amphiphile family display favorable behavior relative to conventional detergents, as tested on multiple membrane protein systems, leading to enhanced structural stability and successful crystallization. MNG amphiphiles are promising tools for membrane protein science because of the ease with which they may be prepared and the facility with which their structures may be varied.

Aspirin exerts its anti-inflammatory effects through selective acetylation of serine 530 on prostaglandin H2 synthase (PGHS). Here we present the 3.4 A resolution X-ray crystal structure of PGHS isoform-1 inactivated by the potent aspirin analogue 2-bromoacetoxy-benzoic acid. Acetylation by this analogue abolishes cyclooxygenase activity by steric blockage of the active-site channel and not through a large conformational change. We observe two rotameric states of the acetyl-serine side chain which block the channel to different extents, a result which may explain the dissimilar effects of aspirin on the two PGHS isoforms. We also observe the product salicylic acid binding at a site consistent with its antagonistic effect on aspirin activity.