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Nielsen, Jens Erik
Preferred name
Nielsen, Jens Erik
Official Name
Nielsen, Jens Erik
Research Output
Now showing 1 - 4 of 4
- PublicationFirst implication of STRA6 mutations in isolated anophthalmia, microphthalmia and coloboma: a new dimension to the STRA6 phenotype(Wiley, 2011-12)
; ; ; ; ; ; ; ; ; ; ; Microphthalmia, anophthalmia, and coloboma (MAC) are structural congenital eye malformations that cause a significant proportion of childhood visual impairments. Several disease genes have been identified but do not account for all MAC cases, suggesting that additional risk loci exist. We used single nucleotide polymorphism (SNP) homozygosity mapping (HM) and targeted next-generation sequencing to identify the causative mutation for autosomal recessive isolated colobomatous microanophthalmia (MCOPCB) in a consanguineous Irish Traveller family. We identified a double-nucleotide polymorphism (g.1157G>A and g.1156G>A; p.G304K) in STRA6 that was homozygous in all of the MCOPCB patients. The STRA6 p.G304K mutation was subsequently detected in additional MCOPCB patients, including one individual with Matthew-Wood syndrome (MWS; MCOPS9). STRA6 encodes a transmembrane receptor involved in vitamin A uptake, a process essential to eye development and growth. We have shown that the G304K mutant STRA6 protein is mislocalized and has severely reduced vitamin A uptake activity. Furthermore, we reproduced the MCOPCB phenotype in a zebrafish disease model by inhibiting retinoic acid (RA) synthesis, suggesting that diminished RA levels account for the eye malformations in STRA6 p.G304K patients. The current study demonstrates that STRA6 mutations can cause isolated eye malformations in addition to the congenital anomalies observed in MWS.194Scopus© Citations 56 - PublicationPredicting the open conformations of protein kinases using molecular dynamics simulationsProtein kinases (PK) control phosphorylation in eukaryotic cells, and thereby regulate metabolic pathways, cell cycle progression, apoptosis and transcription. Consequently there is significant interest in manipulating PK activity and treat diseases by using small-molecule drugs. All PK catalytic domains undergo large conformational changes as a result of substrate binding and phosphorylation. The “closed” state of a PK cataltic domain is the only state able to phosphorylate the target substrate, which makes the two other observed states (the “open” and the “intermediate” states) interesting drug targets. We investigate if MD simulations starting from the closed state of the catalytic domain of protein kinase A (C-PKA) can be used to produce realistic structures representing the intermediate and/or open conformation of C-PKA, since this would allow for drug docking calculations and drug design using MD snapshots. We perform 36 ten-nanosecond MD simulations starting from the closed conformation (PDB ID: 1ATP) of C-PKA in various liganded and phosphorylated states. The results show that MD simulations are capable of reproducing the open conformation of C-PKA with good accuracy within 1 ns of simulation as measured by Cα RMSDs and RMSDs of atoms defining the ATPbinding pocket. Importantly we are able to show that even without knowledge of the structure of the open form of C-PKA, we can identify the MD snapshots resembling the open conformation most using the open structure of a different protein kinase displaying only 23% sequence identity to C-PKA.
2374Scopus© Citations 7 - PublicationProtein Dielectric Constants Determined from NMR Chemical Shift Perturbations(American Chemical Society, 2013-10-14)
; ; ; ; Understanding the connection between protein structure and function requires a quantitative under-standing of electrostatic effects. Structure-based electrostatics calculations are essential for this purpose, but their use has been limited by a long-standing discussion on which value to use for the dielectric constants (εeff and εp) required in Coulombic models and Poisson-Boltzmann models. The currently used values for εeff and εp are essentially empirical parameters calibrated against thermodynamic properties that are indirect measurements of protein electric fields. We determine optimal values for εeff and εp by measuring protein electric fields in solution using direct detection of NMR chemical shift perturbations (CSPs). We measured CSPs in fourteen proteins to get a broad and general characterization of electric fields. Coulomb’s law reproduces the measured CSPs optimally with a protein dielectric constant (εeff) from 3 to 13, with an optimal value across all proteins of 6.5. However, when the water-protein interface is treated with finite difference Poisson-Boltzmann calculations, the optimal protein dielectric constant (εp) rangedsfrom 2-5 with an optimum of 3. It is striking how similar this value is to the dielectric constant of 2-4 measured for protein powders, and how different it is from the εp of 6-20 used in models based on the Poisson-Boltzmann equation when calculating thermodynamic parameters. Because the value of εp = 3 is obtained by analysis of NMR chemical shift perturbations instead of thermodynamic parameters such as pKa values, it is likely to describe only the electric field and thus represent a more general, intrinsic, and transferable εp common to most folded proteins.627Scopus© Citations 70 - PublicationElectrostatics in proteins and protein-ligand complexes(2010-04)
; Accurate computational methods for predicting the electrostatic energies are of major importance for our understanding of protein energetics in general, for computer-aided drug design and in the design of novel biocatalysts and protein therapeutics. Electrostatic energies are of particular importance in applications such as virtual screening, drug design and protein-protein docking due to the high charge densitiy of protein ligands and small-molecule drugs, and the frequent protonation state changes observed when drugs are binding to their protein targets. Therefore, the development of a reliable and fast algorithm for the evaluation of electrostatic free energies, as an important contributor to the overall protein energy function, has been the focus of many scientists for the last three decades. In this review we describe the current state of-the-art in modeling electrostatic effects in proteins and protein-ligand complexes. We focus mainly on the merits and drawbacks of the continuum methodology, and speculate on future directions in refining algorithms for calculating electrostatic energies in proteins using experimental data.805Scopus© Citations 67