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Small-angle scattering makes it possible to solve structural biology problems without special sample preparation, which is typical for such methods as X-ray diffraction on protein crystals or cryoelectronic microscopy of proteins. This review provides examples of using small-angle scattering to solve biological problems. It is proposed to introduce into practice the use of small-angle scattering as a method of quality control of the assembly of proteins and protein complexes, as well as testing the identity of the structural organization of biological objects in the native state in prepared samples before measurements by X-ray diffraction or cryo-electron microscopy. The possibilities of the YUMO small-angle neutron scattering spectrometer on the IBR-2 pulse reactor (Laboratory of Neutron Physics of the Joint Institute for Nuclear Research, Dubna, Russia) for solving a wide range of problems, including in biophysics, structural biology, and biotechnology are shown. The main results of studies of various biological systems using small-angle neutron scattering at the YUMO installation are considered. The possibilities of developing methods of structural biology using small-angle scattering, including protein crystallization, are shown. [ABSTRACT FROM AUTHOR]

Abstract: A correlation between the transition of the oxidative phosphorylation system into a supercomplex state and a change of the functional state of mitochondrial energetics upon the transition from aerobic respiration to hypoxic conditions has been established for the first time. The effect was observed by two different methods in liver and heart mitochondria. The occurrence of highly ordered structures in the membranes of heart mitochondria under hypoxic conditions has been detected by small-angle neutron scattering and electron microscopy during the transition of oxidative phosphorylation into the supercomplex state. The structural parameters of cristae inferred from the data of small-angle neutron scattering and electron microscopy have been compared. The results of measurements using the two methods coincided. Successive exposure to hypoxia and weak osmotic stress signals showed a qualitative difference between these signals. Successive exposure to two signals, with hypoxia as the first one and weak osmotic stress as the second one, was shown to cause impairment of mitochondrial integrity. The effect was observed by small-angle neutron scattering and electron microscopy. Thus, we demonstrated the existence of two qualitatively different signals (hypoxia and osmotic stress), which altered the oxidative phosphorylation system and induced its transition into the supercomplex state. [ABSTRACT FROM AUTHOR]

According to previous studies, ADP/ATP carrier (AAC) can possibly exist as a monomer or in a dimer state in the inner mitochondrial membrane; however, the question on its functional oligomeric state is still open. The aim of the present work is to establish the external factors that could control the functional oligomeric state of AAC (i.e., monomer or dimer). The study is based on the results of our previous work, which revealed that the volume regulation system of mitochondria (MVRS) affects the oxidative phosphorylation (OXPHOS) system: MVRS could transfer OXPHOS system functioning in a state of supercomplex. Consequently, one may expect that the volume regulation system could also control the functional state of AAC during phosphorylation. Here, on rat liver mitochondria we show that, depending on the incubation medium tonicity, AAC functions in two different ways: either as a monomer (in hypotonic and isotonic media) or as a dimer (in a hypertonic medium). Thus, the transition between the monomeric and dimeric forms of AAC is regulated by MVRS, as well as by functioning of OXPHOS. We conclude that the structural reorganization of AAC is associated with the entire OXPHOS reorganization into a supercomplex. It was also found that dimerization of AAC can occur not only due to the action of MVRS (in hypotonic media) but also under hypoxic conditions. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy (TEM) and small-angle neutron scattering (SANS) studies showed that model peptides QNALVCGLRQ (G33) and QNALVCGLRG (G31) corresponding to region 551-560 of the GP protein of the Sudan Ebola virus are prone to oligomerization in solution. Both peptides can form amyloid-like fibrills. The G33 peptide forms fibrils within one day of incubation, whereas the fibrillogenesis of the G31 peptide is observed only after incubation for several months. The possible role of the observed processes in the pathogenesis and the possibility of applying a combination of the TEM and SANS techniques to search for new compounds that are able to influence the protein oligomerization are discussed. [ABSTRACT FROM AUTHOR]

Supramolecular organization of rhodopsin in the photoreceptor membrane was investigated by small-angle neutron scattering method. The experiments, which were performed with mixtures of heavy/light water as solvent (contrast variation method), were aimed at obtaining information about the lipid and protein components of the photoreceptor disc membrane separately. It was shown that the packaging density of the rhodopsin molecules in the photoreceptor membrane was unusually high: the distance between the centers of the molecules was approximately 56 Å. The probability of the monomeric state of rhodopsin molecules in the photoreceptor membrane, according to the data obtained, is rather high. [ABSTRACT FROM AUTHOR]

The structure of the oligomeric protein α-crystallin from bovine eye lens was investigated by small-angle neutron scattering (SANS) with contrast variation. Based on the SANS curves, the match point for α-crystallin (43% DO) and its average scattering length density at this point (2.4•1010 cm) were evaluated. The radius of gyration and the distance distri- bution functions for α-crystallin were calculated. On the basis of these calculations, it was concluded that α-crystallin is characterized by homogeneous distribution of scattering density in the domains inaccessible for water penetration, and all polypeptide subunits in α-crystallin oligomers undergo equal deuteration. The latter indicates that all α-crystallin subunits are equally accessible for water and presumably for some other low molecular weight substances. These conclusions on the α-crystallin structure (homogeneous distribution of scattering density and equal accessibility of all subunits for low molecular weight substances) should be taken into account when elaborating a-crystallin quaternary structure models. [ABSTRACT FROM AUTHOR]

For the first time, the surface of mitoplasts (mitochondria devoid of an outer membrane) was investigated by atomic-force microscopy (AFM). AFM has revealed folds on the surface of mitoplasts with thicknesses of 30–40 nm, which coincides with that of “dry cristae” in mitochondria measured with small-angle neutron scattering and electron microscopy. These results indicate the existence of a specific system maintaining the configuration of a mitoplast membrane similar to that of the inner membrane of intact mitochondria under their swelling in hypotonic conditions. The prospects of using AFM to study the configuration of the surface of the mitochondrial inner membrane and other biological membrane systems were demonstrated. [ABSTRACT FROM AUTHOR]

The ultrastructure of cristae of intact mitochondria, in which the activity of the oxidative phosphorylation system was retained, was investigated by small-angle neutron scattering. Osmotic swelling of organelles was found to cause ultrastructural rearrangements of the inner mitochondrial membrane in rat liver and heart mitochondria. This process was accompanied by the appearance of diffraction peaks indicative of the formation of ordered structures. The lamellar packing of the membranes in heart mitochondria, which is observed under normal conditions, was found to undergo a transition to a nonlamellar hexagonal packing, whose scattering curve shows two peaks with the scattering vectors characterized by a spacing ratio of 1:√3. The electron-microscopy results confirm the possibility of the formation of a hexagonal packing of the inner membrane in heart mitochondria. [ABSTRACT FROM AUTHOR]

The structure of mitochondrial cristae has been studied for the first time by the method of small-angle neutron scattering. Experiments were performed on intact (functioning) mitochondria from rat liver. Mitochondrial cristae are usually considered to be folds of the inner membrane with arbitrary variable intermembrane distances. Under conditions of low-amplitude swelling, mitochondrial cristae transformed into double-membrane structures with a distance of 190 Å between the central planes of the membranes. The formation of double-membrane structures and their structural parameters did not depend on the method for inducing swelling which was accomplished either by placing the mitochondria into a hypotonic medium or through the opening of nonspecific pores. [ABSTRACT FROM AUTHOR]