In this issue

642 Small-angle scattering for structural biology—expanding the frontier while avoiding the pitfalls

David A. Jacques and Jill Trewhella

The number of protein scientists using small-angle scattering has dramatically increased in the past five years largely due to advances in data interpretation tools, but also due to the increasing demand for complementary structural techniques. Small-angle scattering can provide structural data from proteins and protein complexes in relatively dilute solution, including those with inherent structural flexibility. However, the data are inherently one-dimensional and inevitably the researcher wants an interpretation in terms of three-dimensional structures. Reliable interpretation of small-angle scattering data requires understanding of the limitations in the information content and careful practice. As was the case of NMR and crystallography, standards for practice and presentation of data can aid in community-wide acceptance of the reported results. This review provides a roadmap through the small-angle scattering experiment, with a particular focus on quality control and best practice for sample preparation and data analysis as well as critical issues to consider in data interpretation.

881 Structural insights into the molecular mechanism of H-NOX activation

Charles Olea Jr., Mark A. Herzik Jr., John Kuriyan, and Michael A. Marletta

The toxic gas nitric oxide (NO) acts as a signaling molecule in mammals. NO functions through activation of soluble guanylate cyclase (sGC), the mammalian receptor for NO, through binding to the heme cofactor that is contained within an isolable domain. The heme domain of sGC belongs to a larger class of proteins called Heme Nitric oxide/OXygen binding (H-NOX) proteins. NO binding severs the invariant Fe-His bond leading to a displacement away from the proximal helix. In this study, the crystal structure of a mutant that mimics rupture of the Fe-His was solved. This displacement induces heme flattening that is coupled to a significant protein conformational change, which may be a general activation mechanism in the H-NOX protein family.

808 A reported archaeal mechanosensitive channel is a structural homolog of MarR-like transcriptional regulators

Zhenfeng Liu, Troy A. Walton, and Douglas C. Rees

Several archaeal mechanosensitive channels have been reported that confer protection against osmotic downshock conditions, including one from Thermoplasma volcanium designated MscTV. Rather than a membrane protein, however, the crystal structure of this protein reveals a water-soluble protein exhibiting the fold characteristic of the multiple antibiotic resistance regulator (MarR) family of transcriptional regulators. A cell-based osmotic downshock assay further demonstrates that MscTV does not function as a mechanosensitive channel. While the actual biological function remains to be established, Liu, et al. propose that this protein be renamed MLPTv for MarR-like protein from T. volcanium.

631 Lessons from the lysozyme of phage T4

Walter A. Baase, Lijun Liu, Dale E. Tronrud, and Brian W. Matthews

Extensive use of T4 phage lysozyme as a model for protein folding and stability has led some to describe it as the “hydrogen atom” of structural biology. A major purpose of this review is to provide the reader with a complete tabulation of all of the variants that have been characterized, including melting temperatures, crystallographic data, Protein Data Bank access codes, and references to the original literature. Selected results are highlighted.