The year 2005 has been an extremely busy and productive year for the Macromolecular Crystallography (MX) Group. During the year we have seen the installation and commissioning of  the ESRF-EMBL sample changers on all seven end-stations that fall within the remit of the group. The sample changers will fundamentally alter the way in which the beamlines are utilised, and will facilitate the investigation of increasingly complex systems via the screening of a large number of samples.  The latest addition to the MX suite of beamlines became available for users during the autumn. This beamline (ID23-2) is a microfocus beamline 100%  dedicated to MX.  The beamline builds on in-house experience with Kirkpatrick-Baez focussing optics to provide a focal spot size of 9 µm (ultimately to be 5 µm), and is equipped with both a mini-diffractometer and a sample changer. A hectic year of beamline activity was completed by the installation of ADSC Q315r detectors on the beamlines ID23-1, ID29 and ID14-4.  Together with the increasingly reliable and sophisticated automated beamline alignment tools, these beamline developments are outlined in more detail by X. Thibault. The very busy year on the beamlines was complemented, in October, by the completion of the MX Group’s wet lab in the new PSB building. In January 2006 this building was inaugurated in honour of our late Director of Research Carl-Ivar Bränden, and the PSB building is now named in his honour.

The research programme in MX at the ESRF embraces that performed by the external MX community on both the public and CRG beamlines and that carried out by the ESRF in-house team. This latter includes structural biology and methods development as well as the technical developments already discussed.

As the highlights presented in this chapter demonstrate, the trend towards the study of  complex systems shows no sign of abating. The mechanisms of DNA repair in bacterial systems is characterised by the action of  the complex of proteins known as recBCD. The crystal structure analysis of recBCD in complex with DNA has allowed Singleton et al. to propose a mechanism for the process of homologous recombination in bacteria. The outlier in terms of complexity among these articles is the work of Nelson et al., where the ability to investigate microcrystals of the amyloid cross-ß spine has allowed the investigators to propose a mechanism for the formation of amyloid fibrils associated with neurodegenerative diseases.  The circadian rhythm is a fundamental biological mechanism that controls the functioning of our “body clock”. The operation of this system is the subject of the work of  Yidiz et al., where they are able to propose the mechanism of interaction of two of the key components in the circadian cycle of the fruit fly Drosophila. Nature has evolved a number of molecular motors to accomplish motility.  The myosin superfamily groups those motors that progress along an actin filament by conversion of chemical energy into movement. Within this family the action of myosin VI is anomalous due to the inversed directionality the system produces. Ménétry et al. propose an explanation for this apparent anomaly thanks to the high-resolution crystal structure they have obtained using ESRF MX facilities.

The strength of the science carried out on the CRG beamlines is reflected in the contribution of two of the highlights presented in this chapter. Pizarro et al. reveal the structure of Apical Membrane Antigen 1 (AMA1), a candidate for a malaria vaccine that is currently undergoing clinical trials. In the second, an example of combined ESRF/CRG research, Dong et al. report the native structure of a tryptophan 7-halogenase (PrnA) and the structures of PrnA in complex with substrate (tryptophan) and product (7-chloro-tryptophan). Together these structures allow the authors to propose a mechanism for the fantastic regioselectivity of these enzymes. Our examples of research from the public programme concludes with an example of the work that has for many years tested the limits of MX at synchrotron facilities: Wilson et al. have determined the X-ray structure of the ribosome binding domain of RRF (RRF-DI) bound to the large ribosomal subunit of the eubacterium Deinococcus radiodurans and are able to propose a mechanism for ribosomal recycling.

In-house research continues to develop the understanding of the physical and chemical processes underlying the interaction of X-rays with matter and two highlights are presented here. In the first, Nanao et al. turn the “problem” of radiation damage to macromolecular crystals into an opportunity for increased phasing power. It is expected that this method can be extended to become a routine tool for the enhancement of phasing information used in the de novo solution of crystal structures. Finally, Timmins et al. present the crystal structure and mechanism of  maltooligosyltrehalose trehalohydrolase (MTHase) from Deinococcus radiodurans. A presumed forerunner of the extreme radiation  tolerance of this organism to ionising radiation is its tolerance to desiccation. Trehalose appears to be the most effective stabiliser of dried proteins and membranes with the available evidence suggesting  that trehalose protects membranes and proteins by serving as a water substitute. In their report, the authors resolve key questions concerning how this enzyme produces the trehalose that is critical to the extremophile nature of Deinococcus radiodurans.

G. Leonard and S. McSweeney