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Fallon, J. L., Halling, D. B., Hamilton, S. L., & Quiocho, F. A. (2005). Structure of calmodulin bound to the hydrophobic IQ domain of the cardiac Ca(v)1.2 calcium channel. Structure, 13(12), 1881–1886.
Abstract: Ca2+-dependent inactivation (CDI) and facilitation (CDF) of the Ca(v)1.2 Ca2+ channel require calmodulin binding to a putative IQ motif in the carboxy-terminal tail of the pore-forming subunit. We present the 1.45 A crystal structure of Ca2+-calmodulin bound to a 21 residue peptide corresponding to the IQ domain of Ca(v)1.2. This structure shows that parallel binding of calmodulin to the IQ domain is governed by hydrophobic interactions. Mutations of residues I1672 and Q1673 in the peptide to alanines, which abolish CDI but not CDF in the channel, do not greatly alter the structure. Both lobes of Ca2+-saturated CaM bind to the IQ peptide but isoleucine 1672, thought to form an intramolecular interaction that drives CDI, is buried. These findings suggest that this structure could represent the conformation that calmodulin assumes in CDF.
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Klee, E. W., & Zimmermann, M. T. (2019). Molecular modeling of LDLR aids interpretation of genomic variants. Journal of Molecular Medicine, 97(4), 533–540.
Abstract: Genetic variants in low-density lipoprotein receptor (LDLR) are known to cause familial hypercholesterolemia (FH), occurring in up to 1 in 200 people (Youngblom E. et al. 1993 and Nordestgaard BG et al. 34:3478–3490a, 2013) and leading to significant risk for heart disease. Clinical genomics testing using high-throughput sequencing is identifying novel genomic variants of uncertain significance (VUS) in individuals suspected of having FH, but for whom the causal link to the disease remains to be established (Nordestgaard BG et al. 34:3478–3490a, 2013). Unfortunately, experimental data about the atomic structure of the LDL binding domains of LDLR at extracellular pH does not exist. This leads to an inability to apply protein structure-based methods for assessing novel variants identified through genetic testing. Thus, the ambiguities in interpretation of LDLR variants are a barrier to achieving the expected clinical value for personalized genomics assays for management of FH. In this study, we integrated data from the literature and related cellular receptors to develop high-resolution models of full-length LDLR at extracellular conditions and use them to predict which VUS alter LDL binding. We believe that the functional effects of LDLR variants can be resolved using a combination of structural bioinformatics and functional assays, leading to a better correlation with clinical presentation. We have completed modeling of LDLR in two major physiologic conditions, generating detailed hypotheses for how each of the 1007 reported protein variants may affect function. • Hundreds of variants are observed in the LDLR, but most lack interpretation. • Molecular modeling is aided by biochemical knowledge. • We generated context-specific 3D protein models of LDLR. • Our models allowed mechanistic interpretation of many variants. • We interpreted both rare and common genomic variants in their physiologic context. • Effects of genomic variants are often context-specific.
Keywords: gene:LDLR
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Yarham, J. W., Lamichhane, T. N., Pyle, A., Mattijssen, S., Baruffini, E., Bruni, F., et al. (2014). Defective i6A37 modification of mitochondrial and cytosolic tRNAs results from pathogenic mutations in TRIT1 and its substrate tRNA. PLoS genetics, 10(6), e1004424.
Abstract: Identifying the genetic basis for mitochondrial diseases is technically challenging given the size of the mitochondrial proteome and the heterogeneity of disease presentations. Using next-generation exome sequencing, we identified in a patient with severe combined mitochondrial respiratory chain defects and corresponding perturbation in mitochondrial protein synthesis, a homozygous p.Arg323Gln mutation in TRIT1. This gene encodes human tRNA isopentenyltransferase, which is responsible for i6A37 modification of the anticodon loops of a small subset of cytosolic and mitochondrial tRNAs. Deficiency of i6A37 was previously shown in yeast to decrease translational efficiency and fidelity in a codon-specific manner. Modelling of the p.Arg323Gln mutation on the co-crystal structure of the homologous yeast isopentenyltransferase bound to a substrate tRNA, indicates that it is one of a series of adjacent basic side chains that interact with the tRNA backbone of the anticodon stem, somewhat removed from the catalytic center. We show that patient cells bearing the p.Arg323Gln TRIT1 mutation are severely deficient in i6A37 in both cytosolic and mitochondrial tRNAs. Complete complementation of the i6A37 deficiency of both cytosolic and mitochondrial tRNAs was achieved by transduction of patient fibroblasts with wild-type TRIT1. Moreover, we show that a previously-reported pathogenic m.7480A>G mt-tRNASer(UCN) mutation in the anticodon loop sequence A36A37A38 recognised by TRIT1 causes a loss of i6A37 modification. These data demonstrate that deficiencies of i6A37 tRNA modification should be considered a potential mechanism of human disease caused by both nuclear gene and mitochondrial DNA mutations while providing insight into the structure and function of TRIT1 in the modification of cytosolic and mitochondrial tRNAs.
Keywords: genetics; Cells,Cultured; Cytochrome-c Oxidase Deficiency,genetics; Cytosol; DNA,Mitochondrial,genetics; Electron Transport,genetics; Electron Transport Complex IV,genetics; Female; Humans; Male; Mitochondria,genetics; Mitochondrial Diseases,genetics; Protein Biosynthesis,genetics; RNA,Mitochondrial; RNA,Transfer,genetics; Saccharomyces cerevisiae,enzymology,genetics; Schizosaccharomyces,genetics; Schizosaccharomyces pombe Proteins,genetics; Sulfurtransferases,genetics
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Kaczmarska, Z., Ortega, E., Goudarzi, A., Huang, H., Kim, S., Márquez, J. A., et al. (2017). Structure of p300 in complex with acyl-CoA variants. Nature Chemical Biology, 13(27820805), 21–29.
Abstract: Histone acetylation plays an important role in transcriptional activation. Histones are also modified by chemically diverse acylations that are frequently deposited by p300, a transcriptional coactivator that uses a number of different acyl-CoA cofactors. Here we report that while p300 is a robust acetylase, its activity gets weaker with increasing acyl-CoA chain length. Crystal structures of p300 in complex with propionyl-, crotonyl-, or butyryl-CoA show that the aliphatic portions of these cofactors are bound in the lysine substrate-binding tunnel in a conformation that is incompatible with substrate transfer. Lysine substrate binding is predicted to remodel the acyl-CoA ligands into a conformation compatible with acyl-chain transfer. This remodeling requires that the aliphatic portion of acyl-CoA be accommodated in a hydrophobic pocket in the enzymes active site. The size of the pocket and its aliphatic nature exclude long-chain and charged acyl-CoA variants, presumably explaining the cofactor preference for p300.
Keywords: pdb,structural biology,variant assessment
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Crescenzi, O., Tomaselli, S., Guerrini, R., Salvadori, S., D’Ursi, A. M., Temussi, P. A., et al. (2002). Solution structure of the Alzheimer amyloid β‐peptide (1–42) in an apolar microenvironment. European Journal of Biochemistry, 269(22), 5642–5648.
Abstract: The major components of neuritic plaques found in Alzheimer disease (AD) are peptides known as amyloid β-peptides (Aβ), which derive from the proteolitic cleavage of the amyloid precursor proteins. In vitro Aβ may undergo a conformational transition from a soluble form to aggregated, fibrillary β-sheet structures, which seem to be neurotoxic. Alternatively, it has been suggested that an α-helical form can be involved in a process of membrane poration, which would then trigger cellular death. Conformational studies on these peptides in aqueous solution are complicated by their tendency to aggregate, and only recently NMR structures of Aβ-(1–40) and Aβ-(1–42) have been determined in aqueous trifluoroethanol or in SDS micelles. All these studies hint to the presence of two helical regions, connected through a flexible kink, but it proved difficult to determine the length and position of the helical stretches with accuracy and, most of all, to ascertain whether the kink region has a preferred conformation. In the search for a medium which could allow a more accurate structure determination, we performed an exhaustive solvent scan that showed a high propensity of Aβ-(1–42) to adopt helical conformations in aqueous solutions of fluorinated alcohols. The 3D NMR structure of Aβ-(1–42) shows two helical regions encompassing residues 8–25 and 28–38, connected by a regular type I β-turn. The surprising similarity of this structure, as well as the sequence of the C-terminal moiety, with those of the fusion domain of influenza hemagglutinin suggests a direct mechanism of neurotoxicity.
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