Inspecting the ensemble revealed that the models ranked in the top 10% were highly clustered and shared a tight binding interface and single interacting orientation. and complementary capabilities exhibited by methods employed in dynamics studies. We discuss critical factors to be addressed for completing effective structural determinations and expose possible pitfalls of chemical methods. We survey programs developed for facilitating the interpretation of experimental data and discuss possible computational strategies for translating sparse spatial constraints into all-atom models. Examples are provided to illustrate how the concerted application of very diverse probing techniques can lead to the solution of actual biological substrates. Keywords:crosslinking, footprinting, solvent accessibility probes, covalent labeling, structural probing, molecular modeling, structural biology In the last decade, several factors have reawakened a keen interest in the development of chemical methods for the structural elucidation of biopolymers and their assemblies. Driven by the need to understand the function of new gene NVP-LCQ195 NVP-LCQ195 products identified at unprecedented rates, the demand for structural information has greatly intensified as a result of the completion of the Human Genome Project13and large scale proteomics initiatives.4,5The need for 3D-structure elucidation has been further stimulated by the discovery of riboswitches6,7and the realization that sequence information alone is not sufficient to deduce the function of the estimated 98.5% of human genome that does not code for actual proteins.8,9In response to the growing demand, large research centers dedicated to structural genomics have been created in the U.S. and abroad to expand the availability of high-resolution structures and to reduce the cost of structural information.10The weight of these efforts is carried by established high-resolution techniques, such as X-ray crystallography and nuclear magnetic resonance (NMR), which are applicable to a broad range of biopolymers, but present also distinctive restrictions regarding solubility, quantity, size, heterogeneity, and structural flexibility of viable substrates. These intrinsic limitations have been hindering the pursuit of membrane proteins that are marginally soluble in aqueous solvents and highly prone to losing their native fold when removed from the natural lipid bilayer. Size and heterogeneity represent major obstacles to solving larger macromolecular assemblies that are known to support complex cellular functions by clustering together all the necessary components.11The elucidation of these types of substrates could greatly benefit from the implementation of complementary approaches capable of circumventing such limitations. Chemical probing represents an excellent source of structural information for substrates that are not directly amenable to established techniques. Different types of reagents can be employed to identify with NVP-LCQ195 excellent accuracy any susceptible functional group that may be NVP-LCQ195 accessible around the substrate surface, or juxtaposed by its fold.12,13In this way, chemical probing is capable of complementing the classic structural approaches and, ever more frequently, compensating for their inability to obtain high-resolution data, thus enabling the comprehensive structural determination of previously intractable substrates. In the case of known structures, the ability to assess the Rabbit polyclonal to Aquaporin10 yield of modification can provide very valuable information about their dynamics, thus providing the sought-after insights necessary to understand their function. In recent years, the advances made by mass spectrometry (MS) in the characterization of chemically modified biopolymers have presented an excellent opportunity for revisiting structural probing, for increasing its range of applicability, and for exploring new strategies to tackle biological systems of ever increasing complexity. The concomitant development of powerful computational techniques for generating full-fledged models from sparse experimental constraints14,15has greatly increased the value of relatively low-resolution data afforded by chemical probing, thus realizing the possibility of obtaining the actual 3D structure of biopolymers by MS-based technologies (MS3D). In NVP-LCQ195 thisPerspective, we describe the advances fostered by the implementation of MS detection in chemical probing approaches. We discuss experimental considerations to be taken in account when seeking spatial constraints for actual structure determination and point out critical differences with those addressed when investigating structure dynamics. We highlight the progress made by the development of computational tools to support the acquisition of experimental constraints and to translate this type of information into accurate 3D models. == The evolving trajectory of chemical methods in structural biology == Assessing the susceptibility of functional groups to specific chemical reagents constitutes a very versatile strategy.