Courtesy of Amersham Pharmacia Biotech

Detail of the electron density map of deacetoxycephalosporin C synthase from Streptomyces clavuligerus.

Two important approaches can be used to determine the three-dimensional structure of macromolecules. Nuclear magnetic resonance (NMR) spectroscopy yields information on the structure of proteins in solution, but it has a size limitation of approximately 150 amino acid residues (about 16,500 daltons), thereby limiting its usefulness to smaller proteins. In contrast, X-ray crystallography has no apparent size limit for generation of structural data, but it requires crystallization of the target molecule. Owing to recent technical advances, X-ray crystallography is now the preferred method for precise structural determination of proteins.1

In the last five years, researchers have published reports on the nucleotide sequences of several eukaryotic genomes. However, the functions of the majority of gene products from these genomes, including those from the human genome,...

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