Semaphorins are an important class of signalling molecules involved in axon guidance, immune function and angiogenesis. They are characterized by having an extracellular sema domain of about 500 residues. The steps involved in the determination of the structure of human semaphorin 4D are described here as a case study of selenium MAD phasing in a difficult case with low symmetry, moderate diffraction and low selenium content. A particular feature of this study was the large number of diffraction images required to give data of sufficient quality for structure determination and these data are re-analyzed here to investigate the effects of radiation damage on eventual data quality and to suggest strategies for successful MAD phasing in similar difficult cases.

Original publication

DOI

10.1107/s0907444905034992

Type

Journal article

Journal

Acta crystallographica. Section D, Biological crystallography

Publication Date

01/2006

Volume

62

Pages

108 - 115

Addresses

Division of Structural Biology, University of Oxford, Henry Wellcome Building for Genomic Medicine, Roosevelt Drive, Oxford OX3 7BN, England. robert@strubi.ox.ac.uk

Keywords

Humans, Selenium, Semaphorins, Antigens, CD, Antigens, Differentiation, T-Lymphocyte, Ligands, Crystallization, Crystallography, X-Ray, Binding Sites, Protein Conformation, Models, Molecular