The element selenium is incorporated into proteins through the 21st amino acid selenocysteine (Sec). Such selenoproteins are critically important to all types of life, suggesting that being able to accurately decode the Sec codon and correctly placing this amino acid in proteins is biologically fundamental. However, little is known about biosynthesis of selenoproteins in eukaryotic cells. To better understand this process, a team of researchers used data gathered at two APS sectors to determine the crystal structure of the human translational elongation factor responsible for recognizing and delivering the transfer rnA (trnA) carrying Sec to the ribosome …

TAP binding protein, related (TAPbPr), a novel protein chaperone, plays a role in loading peptides onto major histocompatibility class i (mhc i) molecules during the process of immune surveillance. However, until now, how TAPbPr functions in antigen presentation has been unknown. Researchers investigated the biochemical function of TAPbPr, comparing it with tapasin, another chaperone with a similar protein sequence. Using direct binding studies, they demonstrated that TAPbPr functions as a peptide editor, and binds mhc i molecules that are either peptide-free or complexed with low affinity peptides. Because macromolecular crystallography has so far proven unsuccessful for obtaining high-resolution structural information on TAPbPr, the researchers instead collected small-angle x-ray scattering (SAxS) data at the APS. This allowed them to confirm the structural similarities between TAPbPr and tapasin. The results of this study could lead to ways to modulate peptide loading in vaccine design, improving T-cell recognition.

TAPbPr is involved in the intracellular loading of peptides onto mhc i …

Our cells are brilliant biochemists that solve all sorts of chemistry problems under difficult conditions. They speed up slow reactions by orders of magnitude, stuff miles of DNA into tiny spaces, and carefully balance the solubility of different kinds of molecules in a jam-packed cellular solution. A good example is the storage of glucose energy in cells in the form of glycogen. Cells can store up to 55,000 glucose units in water-soluble spheres of branched, polymeric glycogen. This provides ready energy for rapid response to cellular needs but also must be managed carefully because too much glycogen accumulation can activate programmed cell death. This is especially true of neurons, which consume large amounts of glucose but are particularly sensitive to glycogen build-up. One example of what can happen when this basic metabolic process goes awry is observed in Lafora disease, a devastating fatal epilepsy in which mutations in a single key enzyme result in the formation of insoluble glucan inclusion bodies that cause neuronal death. Research conducted at two x-ray beamlines at the U.S. Department of Energy’s Advanced Photon Source (APS), an Office of Science user facility at Argonne solved the structure of the enzyme responsible, the …

The Frank-Starling law of the heart is a basic physiological principle first observed more than 100 years ago. it describes how the heart is able to move blood through the body in a regulated way by pumping out as much blood as it receives. To understand the nature of the molecular mechanism underlying this important regulatory process, researchers from Loyola University together with colleagues from the Illinois Institute of Technology and the University of Wisconsin–Madison conducted x-ray diffraction experiments at the APS to examine myocardial muscles of rats deficient in length-dependent activation (ldA) of muscle fibers in the heart. Their work shows that the protein titin is critically important for transmitting the stretch-induced signals within the heart’s muscles known to impact the strength with which the heart contracts. This work not only solves a piece of …

The dimer structure of an important tumor-suppressing protein, phosphatase and tensin homolog (PTEN), the second most frequently mutated protein found in human cancer, has been established by an international group of researchers carrying out studies using the BioCAT beamline 18ID at the U.S. Department of Energy’s Advanced Photon Source (APS), an Office of Science user facility. Their findings provide new insights into how the protein regulates cell growth and how mutations in the gene that encodes the protein can lead to cancer. The study was published online in Structure, and appeared in the October 6, 2015 issue.

Phosphatase and tensin homolog is a known tumor suppressing protein that is encoded by the PTEN gene. When expressed normally, the protein acts as an enzyme at the cell membrane, instigating a complex biochemical reaction that regulates the cell cycle and prevents cells from growing or dividing in an unregulated fashion. Each …

For many proteins, the ability to change shape is essential for their proper functioning within cells. One longstanding question concerns the process proteins follow when shifting from an unfolded to a three-dimensional globular form. Most previous studies have supported the idea that when an unfolded protein is exposed to native conditions (i.e., to an environment favoring its typically fully-folded, physiological form) a continuous unfolded-to-semi-folded collapse ensues. However, other studies suggest that there is an energetic bottleneck to this step that renders it an all-or-none transition. To resolve the issue, researchers from the University of Massachusetts Medical School and the Illinois Institute of Technology probed the folding stages of cytochrome c, an archetype for protein folding behavior. Its microsecond-scale folding dynamics were unambiguously characterized with Förster resonance energy transfer (FRET) complimented by small angle x-ray scattering (SAXS) carried out at the APS. The SAXS and FRET measurements refuted the conventional view that cytochrome c folding proceeds immediately and smoothly when exposed to native conditions; instead, subpopulations of unfolded and semi-folded protein were observed to coexist during brief intervals. These results provide fundamental insights for biochemistry, as well as for human diseases characterized by protein misfolding, including Parkinson’s, Huntington’s …

Proteases are specialized enzymes responsible for degrading damaged, misfolded, or unneeded proteins within the cell. The human mitochondrial presequence protease (hPreP) breaks down several distinct proteins, including beta amyloid (Aβ) species known to aggregate and form the amyloid plaques associated with Alzheimer’s disease. Using a combination of high-resolution x-ray crystallography and small angle x-ray scattering (SAXS) at the APS, researchers from The University of Chicago and the University of Illinois at Chicago were able to define the mechanism by which hPreP recognizes a diverse array of amyloid proteins. The findings reveal that hPreP uses a large …

How does one kill an infectious invader that is not technically alive? That question has vexed researchers studying prions—aggregates of aberrantly folded protein that propagate by inducing properly folded proteins to convert into misfolded, disease-associated forms—since these infectious agents were identified as the source of a range of devastating neurological diseases such as transmissible spongiform encephalopathies (TSEs), which include Creutzfeldt-Jakob disease and “mad cow disease.” Prions contain no genetic material, so their structure determines their biological activity. That structure, made rigid and insoluble through aberrant protein folding, also makes prions difficult to combat. Researchers used two U.S. Department of Energy synchrotron light sources including the APS to pry out new structural information about prions, yielding insights into the fundamental mechanisms of prion at a level of complexity that has not been observed in short-peptide amyloids used as prion model systems.