The CCP4 (Collaborative Computational Project, Number 4) software suite is a collection of programs and associated data and software libraries which can be used for macromolecular structure determination by X-ray crystallography. The suite is designed to be flexible, allowing users a number of methods of achieving their aims. The programs are from a wide variety of sources but are connected by a common infrastructure provided by standard file formats, data objects and graphical interfaces. Structure solution by macromolecular crystallography is becoming increasingly automated and the CCP4 suite includes several automation pipelines. After giving a brief description of the evolution of CCP4 over the last 30 years, an overview of the current suite is given. While detailed descriptions are given in the accompanying articles, here it is shown how the individual programs contribute to a complete software package.

In the crystal structure of bovine mitochondrial F1-ATPase determined at 2.8 A resolution, the three catalytic beta-subunits differ in conformation and in the bound nucleotide. The structure supports a catalytic mechanism in intact ATP synthase in which the three catalytic subunits are in different states of the catalytic cycle at any instant. Interconversion of the states may be achieved by rotation of the alpha 3 beta 3 subassembly relative to an alpha-helical domain of the gamma-subunit.

iMOSFLM is a graphical user interface to the diffraction dataintegration program MOSFLM. It is designed to simplify data processing by dividing the process into a series of steps, which are normally carried out sequentially. Each step has its own display pane, allowing control over parameters that influence that step and providing graphical feedback to the user. Suitable values for integration parameters are set automatically, but additional menus provide a detailed level of control for experienced users. The image display and the interfaces to the different tasks (indexing, strategy calculation, cell refinement, integration and history) are described. The most important parameters for each step and the best way of assessing success or failure are discussed.

SummaryG protein-coupled receptors play a major role in transmembrane signalling in higher organisms and many are important drug targets. We report the 2.7 Å resolution crystal structure of a β 1 -adrenergic receptor in complex with the high-affinity antagonist cyanopindolol. The modified turkey receptor had been selected to be in its antagonist conformation and its thermostability improved by earlier limited mutagenesis. The ligand-binding pocket comprises 15 side chains from amino acid residues in 4 transmembrane α-helices and extracellular loop 2. This loop defines the entrance of the ligand-binding pocket and is stabilised by two disulphide bonds and a sodium ion. Cyanopindolol binding to the β 1 -adrenergic receptor and carazolol binding to the β 2 -adrenergic receptor involve similar interactions. A short well-defined helix in cytoplasmic loop 2, not observed in either rhodopsin or the β 2 -adrenergic receptor, directly interacts via a tyrosine with the highly conserved DRY motif at the end of helix 3 that is essential for receptor activation.G protein-coupled receptors (GPCRs) are a large family of integral membrane proteins that are prevalent in eukaryotes from yeast to man, and which function as key intermediaries in the transduction of signals from outside to inside the cell1. Activating molecules (agonists), such as hormones and neurotransmitters, bind to GPCRs from the extracellular side of the cell membrane and induce a large conformational change which propagates to the cytoplasmic surface2,3, resulting in activation of G proteins and a consequent change in the level of intracellular messengers such as cAMP, Ca 2+ or signalling lipids. There are over 800 different human GPCRs4, all sharing the characteristic arrangement of 7 transmembrane α-helices with the polypeptide N-terminus on the extracellular side of the plasma membrane5. Analysis of their primary amino acid sequences has resulted in the definition of a number of families6, the largest of which, family A, includes the archetypal GPCR, rhodopsin. The three human β-adrenergic receptor (βAR) subtypes, β 1 , β 2 and β 3 , belong to family A and share 51% sequence identity between Trp 1.31 -Asp 5.73 and Glu 6.30 -Cys H8-Cterm i.e. excluding the N-and C-termini and most of cytoplasmic loop 3 ( Supplementary Fig 1; superscripts refer to Ballesteros-Weinstein numbering7). Drugs that * Joint corresponding authors MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK cgt@mrc-lmb.cam.ac.ukgfx@mrc-lmb.cam.ac.uk Telephone +44-(0)1223-402338 +44-(0)1223-402328 Fax +44-(0)1223-213556 . Author contributions. TW devised and carried out receptor expression, purification, crystallisation and cryo-cooling of the crystals. Receptor stabilisation and baculovirus expression were performed by MJSV; both authors were also involved in data collection and preliminary crystallographic analyses of the crystals. PE helped with the crystal cryo-cooling strategy and in diffraction data collection. JGB performed the functional cAMP and reporter gene assays...