1
|
Bazmi S, Seifi B, Wallin S. Simulations of a protein fold switch reveal crowding-induced population shifts driven by disordered regions. Commun Chem 2023; 6:191. [PMID: 37689829 PMCID: PMC10492864 DOI: 10.1038/s42004-023-00995-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Accepted: 08/24/2023] [Indexed: 09/11/2023] Open
Abstract
Macromolecular crowding effects on globular proteins, which usually adopt a single stable fold, have been widely studied. However, little is known about crowding effects on fold-switching proteins, which reversibly switch between distinct folds. Here we study the mutationally driven switch between the folds of GA and GB, the two 56-amino acid binding domains of protein G, using a structure-based dual-basin model. We show that, in the absence of crowders, the fold populations PA and PB can be controlled by the strengths of contacts in the two folds, κA and κB. A population balance, PA ≈ PB, is obtained for κB/κA = 0.92. The resulting model protein is subject to crowding at different packing fractions, ϕc. We find that crowding increases the GB population and reduces the GA population, reaching PB/PA ≈ 4 at ϕc = 0.44. We analyze the ϕc-dependence of the crowding-induced GA-to-GB switch using scaled particle theory, which provides a qualitative, but not quantitative, fit of our data, suggesting effects beyond a spherical description of the folds. We show that the terminal regions of the protein chain, which are intrinsically disordered only in GA, play a dominant role in the response of the fold switch to crowding effects.
Collapse
Affiliation(s)
- Saman Bazmi
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, NL, A1B 3X7, Canada
| | - Bahman Seifi
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, NL, A1B 3X7, Canada
| | - Stefan Wallin
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, NL, A1B 3X7, Canada.
| |
Collapse
|
2
|
Ranganathan VT, Bazmi S, Wallin S, Liu Y, Yethiraj A. Is Ficoll a Colloid or Polymer? A Multitechnique Study of a Prototypical Excluded-Volume Macromolecular Crowder. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c00677] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
| | - Saman Bazmi
- Department of Physics and Physical Oceanography, Memorial University, St. John’s, NLA1B 3X7, Canada
| | - Stefan Wallin
- Department of Physics and Physical Oceanography, Memorial University, St. John’s, NLA1B 3X7, Canada
| | - Yun Liu
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland20899, United States
- Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware19716, United States
| | - Anand Yethiraj
- Department of Physics and Physical Oceanography, Memorial University, St. John’s, NLA1B 3X7, Canada
| |
Collapse
|
3
|
Bazmi S, Wallin S. Crowding-induced protein destabilization in the absence of soft attractions. Biophys J 2022; 121:2503-2513. [PMID: 35672949 DOI: 10.1016/j.bpj.2022.06.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Revised: 04/18/2022] [Accepted: 06/01/2022] [Indexed: 11/02/2022] Open
Abstract
It is generally assumed that volume exclusion by macromolecular crowders universally stabilizes the native states of proteins and destabilization suggests soft attractions between crowders and protein. Here we show that proteins can be destabilized even by crowders that are purely repulsive. With a coarse-grained sequence-based model, we study the folding thermodynamics of two sequences with different native folds, a helical hairpin and a β-barrel, in a range of crowder volume fractions, φc. We find that the native state, N, remains structurally unchanged under crowded conditions, while the size of the unfolded state, U, decreases monotonically with φc. Hence, for all φc>0, U is entropically disfavored relative to N. This entropy-centric view holds for the helical hairpin protein, which is stabilized under all crowded conditions as quantified by changes in either the folding midpoint temperature, Tm, or the free energy of folding. We find, however, that the β-barrel protein is destabilized under low-T, low-φc conditions. This destabilization can be understood from two characteristics of its folding: 1) a relatively compact U at T<Tm, such that U is only weakly disfavored entropically by the crowders; and 2) a transient, compact, and relatively low-energy nonnative state that has a maximum population of only a few percent at φc=0, but increasing monotonically with φc. Overall, protein destabilization driven by hard-core effects appears possible when a compaction of U leads to even a modest population of compact nonnative states that are energetically competitive with N.
Collapse
Affiliation(s)
- Saman Bazmi
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St Johns, Newfoundland and Labrador, Canada
| | - Stefan Wallin
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St Johns, Newfoundland and Labrador, Canada.
| |
Collapse
|
4
|
Seifi B, Wallin S. The C-terminal domain of transcription factor RfaH: Folding, fold switching and energy landscape. Biopolymers 2021; 112:e23420. [PMID: 33521926 DOI: 10.1002/bip.23420] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 01/12/2021] [Accepted: 01/14/2021] [Indexed: 12/27/2022]
Abstract
We simulate the folding and fold switching of the C-terminal domain (CTD) of the transcription factor RfaH using an all-atom physics-based model augmented with a dual-basin structure-based potential energy term. We show that this hybrid model captures the essential thermodynamic behavior of this metamorphic domain, that is, a change in the global free energy minimum from an α-helical hairpin to a 5-stranded β-barrel upon the dissociation of the CTD from the rest of the protein. Using Monte Carlo sampling techniques, we then analyze the energy landscape of the CTD in terms of progress variables for folding toward the two folds. We find that, below the folding transition, the energy landscape is characterized by a single, dominant funnel to the native β-barrel structure. The absence of a deep funnel to the α-helical hairpin state reflects a negligible population of this fold for the isolated CTD. We observe, however, a higher α-helix structure content in the unfolded state compared to results from a similar but fold switch-incompetent version of our model. Moreover, in folding simulations started from an extended chain conformation we find transiently formed α-helical structure, occurring early in the process and disappearing as the chain progresses toward the thermally stable β-barrel state.
Collapse
Affiliation(s)
- Bahman Seifi
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St Johns, Canada
| | - Stefan Wallin
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St Johns, Canada
| |
Collapse
|
5
|
Seifi B, Aina A, Wallin S. Structural fluctuations and mechanical stabilities of the metamorphic protein RfaH. Proteins 2020; 89:289-300. [PMID: 32996201 DOI: 10.1002/prot.26014] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Revised: 07/17/2020] [Accepted: 08/31/2020] [Indexed: 01/08/2023]
Abstract
RfaH is a compact two-domain bacterial transcription factor that functions both as a regulator of transcription and an enhancer of translation. Underpinning the dual functional roles of RfaH is a partial but dramatic fold switch, which completely transforms the ~50-amino acid C-terminal domain (CTD) from an all-α state to an all-β state. The fold switch of the CTD occurs when RfaH binds to RNA polymerase (RNAP), however, the details of how this structural transformation is triggered is not well understood. Here we use all-atom Monte Carlo simulations to characterize structural fluctuations and mechanical stability properties of the full-length RfaH and the CTD as an isolated fragment. In agreement with experiments, we find that interdomain contacts are crucial for maintaining a stable, all-α CTD in free RfaH. To probe mechanical properties, we use pulling simulations to measure the work required to inflict local deformations at different positions along the chain. The resulting mechanical stability profile reveals that free RfaH can be divided into a "rigid" part and a "soft" part, with a boundary that nearly coincides with the boundary between the two domains. We discuss the potential role of this feature for how fold switching may be triggered by interaction with RNAP.
Collapse
Affiliation(s)
- Bahman Seifi
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St Johns, Newfoundland, Canada
| | - Adekunle Aina
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St Johns, Newfoundland, Canada
| | - Stefan Wallin
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St Johns, Newfoundland, Canada
| |
Collapse
|
6
|
Trotter D, Wallin S. Effects of Topology and Sequence in Protein Folding Linked via Conformational Fluctuations. Biophys J 2020; 118:1370-1380. [PMID: 32061276 DOI: 10.1016/j.bpj.2020.01.020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Revised: 12/17/2019] [Accepted: 01/13/2020] [Indexed: 01/18/2023] Open
Abstract
Experiments have compared the folding of proteins with different amino acid sequences but the same basic structure, or fold. Results indicate that folding is robust to sequence variations for proteins with some nonlocal folds, such as all-β, whereas the folding of more local, all-α proteins typically exhibits a stronger sequence dependence. Here, we use a coarse-grained model to systematically study how variations in sequence perturb the folding energy landscapes of three model sequences with 3α, 4β + α, and β-barrel folds, respectively. These three proteins exhibit folding features in line with experiments, including expected rank order in the cooperativity of the folding transition and stability-dependent shifts in the location of the free-energy barrier to folding. Using a generalized-ensemble simulation approach, we determine the thermodynamics of around 2000 sequence variants representing all possible hydrophobic or polar single- and double-point mutations. From an analysis of the subset of stability-neutral mutations, we find that folding is perturbed in a topology-dependent manner, with the β-barrel protein being the most robust. Our analysis shows, in particular, that the magnitude of mutational perturbations of the transition state is controlled in part by the size or "width" of the underlying conformational ensemble. This result suggests that the mutational robustness of the folding of the β-barrel protein is underpinned by its conformationally restricted transition state ensemble, revealing a link between sequence and topological effects in protein folding.
Collapse
Affiliation(s)
- Daniel Trotter
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, Newfoundland, Canada
| | - Stefan Wallin
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, Newfoundland, Canada.
| |
Collapse
|
7
|
Robichaud NAS, Saika-Voivod I, Wallin S. Phase behavior of blocky charge lattice polymers: Crystals, liquids, sheets, filaments, and clusters. Phys Rev E 2019; 100:052404. [PMID: 31869935 DOI: 10.1103/physreve.100.052404] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Indexed: 12/30/2022]
Abstract
Motivated by the idea that intrinsically disordered proteins (IDPs) condense into liquidlike droplets within cells, we carry out Monte Carlo simulations of a polymer lattice model to study the relationship between charge patterning and phase separation. Polymer chains containing neutral, positively charged, and negatively charged monomers are placed on a cubic lattice. Only nearest-neighbor interactions between charges are considered. We determine the phase diagram for a systematically varied set of sequences. We observe homogeneous fluids, liquid condensation, cluster phases, filaments, and crystal states. Of the six sequences we study, three form crystals at low temperatures. The other three sequences, which have lower charge densities, instead collapse into gel-like networks or unconnected finite clusters. Longer neutral patches along the sequence sterically limit the size and shape of low-energy structures, which is analogous to the effect of charge or limited valence in attractive colloids. Only one sequence clearly exhibits liquid behavior; this sequence has a reduced tendency to individually fold and crystallize compared to others of similar charge density and draws parallels to real IDP behavior.
Collapse
Affiliation(s)
- Nicholas A S Robichaud
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X7
| | - Ivan Saika-Voivod
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X7
| | - Stefan Wallin
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X7
| |
Collapse
|
8
|
Wallin S, Trotter D. Interplay between Native State Topology and Sequence in Two-State Protein Folding. Biophys J 2019. [DOI: 10.1016/j.bpj.2018.11.1840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
|
9
|
Coady BM, Marshall JD, Hattie LE, Brannan AM, Fitzpatrick MN, Hickey KE, Wallin S, Booth V, Brown RJ. Characterization of a peptide containing the major heparin binding domain of human hepatic lipase. J Pept Sci 2018; 24:e3123. [DOI: 10.1002/psc.3123] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Revised: 08/09/2018] [Accepted: 08/31/2018] [Indexed: 11/08/2022]
Affiliation(s)
- Breanne M. Coady
- Department of Biochemistry; Memorial University of Newfoundland; St. John's NL Canada
| | - Jenika D. Marshall
- Department of Biochemistry; Memorial University of Newfoundland; St. John's NL Canada
| | - Luke E. Hattie
- Department of Biochemistry; Memorial University of Newfoundland; St. John's NL Canada
| | - Alexander M. Brannan
- Department of Biochemistry; Memorial University of Newfoundland; St. John's NL Canada
| | | | - Kala E. Hickey
- Department of Biochemistry; Memorial University of Newfoundland; St. John's NL Canada
| | - Stefan Wallin
- Department of Physics and Physical Oceanography; Memorial University of Newfoundland; St. John's NL Canada
| | - Valerie Booth
- Department of Biochemistry; Memorial University of Newfoundland; St. John's NL Canada
- Department of Physics and Physical Oceanography; Memorial University of Newfoundland; St. John's NL Canada
| | - Robert J. Brown
- Department of Biochemistry; Memorial University of Newfoundland; St. John's NL Canada
| |
Collapse
|
10
|
Zhu L, Petrlova J, Gysbers P, Hebert H, Wallin S, Jegerschöld C, Lagerstedt JO. Structures of apolipoprotein A-I in high density lipoprotein generated by electron microscopy and biased simulations. Biochim Biophys Acta Gen Subj 2017; 1861:2726-2738. [DOI: 10.1016/j.bbagen.2017.07.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2017] [Revised: 07/18/2017] [Accepted: 07/24/2017] [Indexed: 10/19/2022]
|
11
|
Aina A, Wallin S. Multisequence algorithm for coarse-grained biomolecular simulations: Exploring the sequence-structure relationship of proteins. J Chem Phys 2017; 147:095102. [DOI: 10.1063/1.4986933] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Affiliation(s)
- A. Aina
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador A1B 3X7, Canada
| | - S. Wallin
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador A1B 3X7, Canada
| |
Collapse
|
12
|
Holzgräfe C, Wallin S. Smooth functional transition along a mutational pathway with an abrupt protein fold switch. Biophys J 2015; 107:1217-1225. [PMID: 25185557 DOI: 10.1016/j.bpj.2014.07.020] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2014] [Revised: 06/25/2014] [Accepted: 07/01/2014] [Indexed: 10/24/2022] Open
Abstract
Recent protein design experiments have demonstrated that proteins can migrate between folds through the accumulation of substitution mutations without visiting disordered or nonfunctional points in sequence space. To explore the biophysical mechanism underlying such transitions we use a three-letter continuous protein model with seven atoms per amino acid to provide realistic sequence-structure and sequence-function mappings through explicit simulation of the folding and interaction of model sequences. We start from two 16-amino-acid sequences folding into an α-helix and a β-hairpin, respectively, each of which has a preferred binding partner with 35 amino acids. We identify a mutational pathway between the two folds, which features a sharp fold switch. By contrast, we find that the transition in function is smooth. Moreover, the switch in preferred binding partner does not coincide with the fold switch. Discovery of new folds in evolution might therefore be facilitated by following fitness slopes in sequence space underpinned by binding-induced conformational switching.
Collapse
Affiliation(s)
- Christian Holzgräfe
- Department of Astronomy and Theoretical Physics, Computational Biology and Biological Physics, Lund University, Lund, Sweden
| | - Stefan Wallin
- Department of Astronomy and Theoretical Physics, Computational Biology and Biological Physics, Lund University, Lund, Sweden.
| |
Collapse
|
13
|
Wallin S, Gambacorta L, Kotova N, Warensjö Lemming E, Nälsén C, Solfrizzo M, Olsen M. Biomonitoring of concurrent mycotoxin exposure among adults in Sweden through urinary multi-biomarker analysis. Food Chem Toxicol 2015; 83:133-9. [DOI: 10.1016/j.fct.2015.05.023] [Citation(s) in RCA: 86] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Revised: 05/20/2015] [Accepted: 05/21/2015] [Indexed: 01/01/2023]
|
14
|
|
15
|
Petrlova J, Bhattacherjee A, Boomsma W, Wallin S, Lagerstedt JO, Irbäck A. Conformational and aggregation properties of the 1-93 fragment of apolipoprotein A-I. Protein Sci 2014; 23:1559-71. [PMID: 25131953 DOI: 10.1002/pro.2534] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Revised: 07/11/2014] [Accepted: 08/04/2014] [Indexed: 11/12/2022]
Abstract
Several disease-linked mutations of apolipoprotein A-I, the major protein in high-density lipoprotein (HDL), are known to be amyloidogenic, and the fibrils often contain N-terminal fragments of the protein. Here, we present a combined computational and experimental study of the fibril-associated disordered 1-93 fragment of this protein, in wild-type and mutated (G26R, S36A, K40L, W50R) forms. In atomic-level Monte Carlo simulations of the free monomer, validated by circular dichroism spectroscopy, we observe changes in the position-dependent β-strand probability induced by mutations. We find that these conformational shifts match well with the effects of these mutations in thioflavin T fluorescence and transmission electron microscopy experiments. Together, our results point to molecular mechanisms that may have a key role in disease-linked aggregation of apolipoprotein A-I.
Collapse
Affiliation(s)
- Jitka Petrlova
- Department of Experimental Medical Science, Lund University, BMC Floor C12, SE-221 84, Lund, Sweden
| | | | | | | | | | | |
Collapse
|
16
|
Holzgräfe C, Wallin S. Smooth Functional Transition Along a Mutational Pathway with an Abrupt Protein Fold Switch. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.2465] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
|
17
|
Wallin S, Hardie L, Kotova N, Lemming EW, Nälsén C, Ridefelt P, Turner P, White K, Olsen M. Biomonitoring study of deoxynivalenol exposure and association with typical cereal consumption in Swedish adults. WORLD MYCOTOXIN J 2013. [DOI: 10.3920/wmj2013.1581] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Deoxynivalenol (DON) is a mycotoxin of the trichothecene family commonly found in cereals infested with different Fusarium species. DON acts primarily on the gastrointestinal and immune system and is suspected to be an underlying agent causing several outbreaks of gastrointestinal disorder among humans, which prompts studies of human exposure and estimations of intake among populations. However, assessing human exposure to mycotoxins is associated with several difficulties. Therefore, a study was undertaken among adults (18-80 years) in a subgroup of Riksmaten, the Swedish national survey investigating dietary habits, examining both the association between urinary DON concentration and dietary intake of cereals, and estimations of daily DON intake. The results indicate that exposure to DON is common among Swedish adults, as this mycotoxin was detected in 292 out of 326 urine samples (90%) at levels ranging from non-detectable to 65.8 ng DON/ml urine with a median level of 2.9 ng/ml. Furthermore, urinary DON (ng/mg creatinine) was associated with intake (g/day) of total cereal grain as well as whole grain. Urinary DON was also significantly associated with breakfast cereals and porridge consumption (P<0.05). Estimated DON intake in this study ranged between 2.5 and 5,443 ng/kg body weight (bw). 1% of the individuals had estimated intakes above the group provisional maximum tolerable daily intake (PMTDI; 1 μg/kg), whereas the mean and median intakes of 159 and 84 ng DON/kg bw, respectively, were considerably below the PMTDI. Along with the toxicological profile of DON, no serious health implications are to be expected for the majority of Swedish adults, although a potential health concern remains for some high cereal consumers. In conclusion, biomonitoring could prove to be a valuable tool for observing DON exposure among populations.
Collapse
Affiliation(s)
- S. Wallin
- National Food Agency, P.O. Box 622, 75126 Uppsala, Sweden
| | - L.J. Hardie
- Division of Epidemiology, Leeds Institute for Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - N. Kotova
- National Food Agency, P.O. Box 622, 75126 Uppsala, Sweden
| | | | - C. Nälsén
- National Food Agency, P.O. Box 622, 75126 Uppsala, Sweden
| | - P. Ridefelt
- Department of Medical Sciences, Section Clinical Chemistry, Uppsala University, University Hospital, 75185 Uppsala, Sweden
| | - P.C. Turner
- Maryland Institute for Applied Environmental Health, School of Public Health, University of Maryland, College Park, MD 20742, USA
| | - K.L.M. White
- Division of Epidemiology, Leeds Institute for Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - M. Olsen
- National Food Agency, P.O. Box 622, 75126 Uppsala, Sweden
| |
Collapse
|
18
|
Bhattacherjee A, Wallin S. Exploring Protein-Peptide Binding Specificity through Computational Peptide Screening. PLoS Comput Biol 2013; 9:e1003277. [PMID: 24204228 PMCID: PMC3812049 DOI: 10.1371/journal.pcbi.1003277] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2013] [Accepted: 08/30/2013] [Indexed: 11/19/2022] Open
Abstract
The binding of short disordered peptide stretches to globular protein domains is important for a wide range of cellular processes, including signal transduction, protein transport, and immune response. The often promiscuous nature of these interactions and the conformational flexibility of the peptide chain, sometimes even when bound, make the binding specificity of this type of protein interaction a challenge to understand. Here we develop and test a Monte Carlo-based procedure for calculating protein-peptide binding thermodynamics for many sequences in a single run. The method explores both peptide sequence and conformational space simultaneously by simulating a joint probability distribution which, in particular, makes searching through peptide sequence space computationally efficient. To test our method, we apply it to 3 different peptide-binding protein domains and test its ability to capture the experimentally determined specificity profiles. Insight into the molecular underpinnings of the observed specificities is obtained by analyzing the peptide conformational ensembles of a large number of binding-competent sequences. We also explore the possibility of using our method to discover new peptide-binding pockets on protein structures. The interactions between proteins play a crucial role for almost every undertaking of a cell. Many of these interactions are mediated by the binding of relatively short unstructured polypeptide segments, or peptides, in one protein to well-folded domains in other proteins. Such protein-peptide interactions have some interesting and special properties, e.g., promiscuity, which means many different peptide sequences are able to bind the same protein domain. Peptides also often exhibit structural flexibility even after binding a protein. These special properties make it desirable, but also challenging, to simulate protein-peptide binding in atomistic detail for many different peptide sequences. To this end, we have developed a computational algorithm that simultaneously explores the structure of protein-peptide complexes and the amino acid sequences of the peptide. In particular, our algorithm allows binding-competent peptide sequences to be generated in direct relation to their binding strengths. We also explored the possibility of using our method to locate new peptide-binding pockets on protein structures. Computational algorithms such as the one developed here may pave the way to reveal the full complexity of protein-protein interaction networks used in cells.
Collapse
Affiliation(s)
- Arnab Bhattacherjee
- Department of Astronomy and Theoretical Physics, Computational Biology and Biological Physics group, Lund University, Lund, Sweden
| | - Stefan Wallin
- Department of Astronomy and Theoretical Physics, Computational Biology and Biological Physics group, Lund University, Lund, Sweden
- * E-mail:
| |
Collapse
|
19
|
Abstract
We present and study a minimal structure-based model for the self-assembly of peptides into ordered β-sheet-rich fibrils. The peptides are represented by unit-length sticks on a cubic lattice and interact by hydrogen bonding and hydrophobicity forces. Using Monte Carlo simulations with >10(5) peptides, we show that fibril formation occurs with sigmoidal kinetics in the model. To determine the mechanism of fibril nucleation, we compute the joint distribution in length and width of the aggregates at equilibrium, using an efficient cluster move and flat-histogram techniques. This analysis, based on simulations with 256 peptides in which aggregates form and dissolve reversibly, shows that the main free-energy barriers that a nascent fibril has to overcome are associated with changes in width.
Collapse
Affiliation(s)
- Anders Irbäck
- Computational Biology and Biological Physics, Department of Astronomy and Theoretical Physics, Lund University, Sölvegatan 14A, SE-223 62 Lund, Sweden
| | | | | | | | | |
Collapse
|
20
|
Follin E, Karlsson M, Lundegaard C, Nielsen M, Wallin S, Paulsson K, Westerdahl H. In silico peptide-binding predictions of passerine MHC class I reveal similarities across distantly related species, suggesting convergence on the level of protein function. Immunogenetics 2013; 65:299-311. [PMID: 23358931 DOI: 10.1007/s00251-012-0676-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2012] [Accepted: 12/24/2012] [Indexed: 11/26/2022]
Abstract
The major histocompatibility complex (MHC) genes are the most polymorphic genes found in the vertebrate genome, and they encode proteins that play an essential role in the adaptive immune response. Many songbirds (passerines) have been shown to have a large number of transcribed MHC class I genes compared to most mammals. To elucidate the reason for this large number of genes, we compared 14 MHC class I alleles (α1-α3 domains), from great reed warbler, house sparrow and tree sparrow, via phylogenetic analysis, homology modelling and in silico peptide-binding predictions to investigate their functional and genetic relationships. We found more pronounced clustering of the MHC class I allomorphs (allele specific proteins) in regards to their function (peptide-binding specificities) compared to their genetic relationships (amino acid sequences), indicating that the high number of alleles is of functional significance. The MHC class I allomorphs from house sparrow and tree sparrow, species that diverged 10 million years ago (MYA), had overlapping peptide-binding specificities, and these similarities across species were also confirmed in phylogenetic analyses based on amino acid sequences. Notably, there were also overlapping peptide-binding specificities in the allomorphs from house sparrow and great reed warbler, although these species diverged 30 MYA. This overlap was not found in a tree based on amino acid sequences. Our interpretation is that convergent evolution on the level of the protein function, possibly driven by selection from shared pathogens, has resulted in allomorphs with similar peptide-binding repertoires, although trans-species evolution in combination with gene conversion cannot be ruled out.
Collapse
Affiliation(s)
- Elna Follin
- Immunology Section, BMC-D14, Department of Experimental Medical Sciences, Lund University, 221 84, Lund, Sweden.
| | | | | | | | | | | | | |
Collapse
|
21
|
Abstract
We study the thermodynamic behavior of a model protein with 54 amino acidsthat is designed to form a three-helix bundle in its native state. The model contains three types of amino acids and five to six atoms per amino acid, and has the Ramachandran torsion angles as its only degrees of freedom.The force field is based on hydrogen bonds and effective hydrophobicity forces. We study how the character of the collapse transition depends on the strengths of these forces. For a suitable choice of these two parameters, it is found that the collapse transition is first-order-like and coincides with the folding transition. Also shown is that the corresponding one- and two-helix segments make less stable secondary structure than the three-helix sequence.
Collapse
Affiliation(s)
- A Irbäck
- Complex Systems Division, Department of Theoretical Physics, Lund University, Sölvegatan 14A, S-223 62 Lund, Sweden
| | | | | |
Collapse
|
22
|
Olsson N, Wallin S, James P, Borrebaeck CAK, Wingren C. Epitope-specificity of recombinant antibodies reveals promiscuous peptide-binding properties. Protein Sci 2012; 21:1897-910. [PMID: 23034898 DOI: 10.1002/pro.2173] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Accepted: 09/26/2012] [Indexed: 01/25/2023]
Abstract
Protein-peptide interactions are a common occurrence and essential for numerous cellular processes, and frequently explored in broad applications within biology, medicine, and proteomics. Therefore, understanding the molecular mechanism(s) of protein-peptide recognition, specificity, and binding interactions will be essential. In this study, we report the first detailed analysis of antibody-peptide interaction characteristics, by combining large-scale experimental peptide binding data with the structural analysis of eight human recombinant antibodies and numerous peptides, targeting tryptic mammalian and eukaryote proteomes. The results consistently revealed that promiscuous peptide-binding interactions, that is, both specific and degenerate binding, were exhibited by all antibodies, and the discovery was corroborated by orthogonal data, indicating that this might be a general phenomenon for low-affinity antibody-peptide interactions. The molecular mechanism for the degenerate peptide-binding specificity appeared to be executed through the use of 2-3 semi-conserved anchor residues in the C-terminal part of the peptides, in analogue to the mechanism utilized by the major histocompatibility complex-peptide complexes. In the long-term, this knowledge will be instrumental for advancing our fundamental understanding of protein-peptide interactions, as well as for designing, generating, and applying peptide specific antibodies, or peptide-binding proteins in general, in various biotechnical and medical applications.
Collapse
Affiliation(s)
- Niclas Olsson
- Department of Immunotechnology, Lund University, Lund, Sweden
| | | | | | | | | |
Collapse
|
23
|
Staneva I, Huang Y, Liu Z, Wallin S. Binding of two intrinsically disordered peptides to a multi-specific protein: a combined Monte Carlo and molecular dynamics study. PLoS Comput Biol 2012; 8:e1002682. [PMID: 23028280 PMCID: PMC3441455 DOI: 10.1371/journal.pcbi.1002682] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Accepted: 07/20/2012] [Indexed: 11/27/2022] Open
Abstract
The unique ability of intrinsically disordered proteins (IDPs) to fold upon binding to partner molecules makes them functionally well-suited for cellular communication networks. For example, the folding-binding of different IDP sequences onto the same surface of an ordered protein provides a mechanism for signaling in a many-to-one manner. Here, we study the molecular details of this signaling mechanism by applying both Molecular Dynamics and Monte Carlo methods to S100B, a calcium-modulated homodimeric protein, and two of its IDP targets, p53 and TRTK-12. Despite adopting somewhat different conformations in complex with S100B and showing no apparent sequence similarity, the two IDP targets associate in virtually the same manner. As free chains, both target sequences remain flexible and sample their respective bound, natively -helical states to a small extent. Association occurs through an intermediate state in the periphery of the S100B binding pocket, stabilized by nonnative interactions which are either hydrophobic or electrostatic in nature. Our results highlight the importance of overall physical properties of IDP segments, such as net charge or presence of strongly hydrophobic amino acids, for molecular recognition via coupled folding-binding. A substantial fraction of our proteins are believed to be partly or completely disordered, meaning that they contain regions that lack a stable folded structure under typical physiological conditions. This is a feature which plays a key role in their functions. For example, it allows them to have many structurally different binding partners which in turn permits the construction of the intricate signaling and regulatory networks necessary to sustain complex biological organisms such as ourselves. Whereas measuring the binding strengths of associations involving disordered proteins is routine, the binding process itself is today still not fully understood. We use two different computational models to study the interactions of a folded protein, S100B, which can bind various disordered peptides. In particular, we compare two peptides whose structures are known when in complex with S100B. Our results suggest that, although the peptides assume different structures in the bound state, there are similarities in how they associate with S100B. The possibility to computationally model the interplay between proteins is an important complement to experiments, by identifying crucial steps in the binding process. This is essential to understand, e.g., how single mutations sometimes lead to serious diseases.
Collapse
Affiliation(s)
- Iskra Staneva
- Department of Astronomy and Theoretical Physics, Computational Biology and Biological Physics group, Lund University, Lund, Sweden
| | - Yongqi Huang
- College of Chemistry and Molecular Engineering, and Center for Quantitative Biology, Peking University, Beijing, China
| | - Zhirong Liu
- College of Chemistry and Molecular Engineering, and Center for Quantitative Biology, Peking University, Beijing, China
| | - Stefan Wallin
- Department of Astronomy and Theoretical Physics, Computational Biology and Biological Physics group, Lund University, Lund, Sweden
- * E-mail:
| |
Collapse
|
24
|
Bhattacherjee A, Wallin S. Coupled folding-binding in a hydrophobic/polar protein model: impact of synergistic folding and disordered flanks. Biophys J 2012; 102:569-78. [PMID: 22325280 DOI: 10.1016/j.bpj.2011.12.008] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2011] [Revised: 11/18/2011] [Accepted: 12/01/2011] [Indexed: 11/28/2022] Open
Abstract
Coupled folding-binding is central to the function of many intrinsically disordered proteins, yet not fully understood. With a continuous three-letter protein model, we explore the free-energy landscape of pairs of interacting sequences and how it is impacted by 1), variations in the binding mechanism; and 2), the addition of disordered flanks to the binding region. In particular, we focus on two sequences, one with 16 and one with 35 amino acids, which make a stable dimeric three-helix bundle at low temperatures. Three distinct binding mechanisms are realized by altering the stabilities of the individual monomers: docking, coupled folding-binding of a single α-helix, and synergistic folding and binding. Compared to docking, the free-energy barrier for binding is reduced when the single α-helix is allowed to fold upon binding, but only marginally. A greater reduction is found for synergistic folding, which in addition results in a binding transition state characterized by very few interchain contacts. Disordered flanking chain segments attached to the α-helix sequence can, despite a negligible impact on the dimer stability, lead to a downhill free-energy surface in which the barrier for binding is eliminated.
Collapse
Affiliation(s)
- Arnab Bhattacherjee
- Computational Biology and Biological Physics, Department of Astronomy and Theoretical Physics, Lund University, Lund, Sweden
| | | |
Collapse
|
25
|
Chan HS, Zhang Z, Wallin S, Liu Z. Cooperativity, local-nonlocal coupling, and nonnative interactions: principles of protein folding from coarse-grained models. Annu Rev Phys Chem 2011; 62:301-26. [PMID: 21453060 DOI: 10.1146/annurev-physchem-032210-103405] [Citation(s) in RCA: 172] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Coarse-grained, self-contained polymer models are powerful tools in the study of protein folding. They are also essential to assess predictions from less rigorous theoretical approaches that lack an explicit-chain representation. Here we review advances in coarse-grained modeling of cooperative protein folding, noting in particular that the Levinthal paradox was raised in response to the experimental discovery of two-state-like folding in the late 1960s, rather than to the problem of conformational search per se. Comparisons between theory and experiment indicate a prominent role of desolvation barriers in cooperative folding, which likely emerges generally from a coupling between local conformational preferences and nonlocal packing interactions. Many of these principles have been elucidated by native-centric models, wherein nonnative interactions may be treated perturbatively. We discuss these developments as well as recent applications of coarse-grained chain modeling to knotted proteins and to intrinsically disordered proteins.
Collapse
Affiliation(s)
- Hue Sun Chan
- Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
| | | | | | | |
Collapse
|
26
|
Abstract
An increasing number of proteins are being discovered with a remarkable and somewhat surprising feature, a knot in their native structures. How the polypeptide chain is able to "knot" itself during the folding process to form these highly intricate protein topologies is not known. Here we perform a computational study on the 160-amino-acid homodimeric protein YibK, which, like other proteins in the SpoU family of MTases, contains a deep trefoil knot in its C-terminal region. In this study, we use a coarse-grained C(alpha)-chain representation and Langevin dynamics to study folding kinetics. We find that specific, attractive nonnative interactions are critical for knot formation. In the absence of these interactions, i.e., in an energetics driven entirely by native interactions, knot formation is exceedingly unlikely. Further, we find, in concert with recent experimental data on YibK, two parallel folding pathways that we attribute to an early and a late formation of the trefoil knot, respectively. For both pathways, knot formation occurs before dimerization. A bioinformatics analysis of the SpoU family of proteins reveals further that the critical nonnative interactions may originate from evolutionary conserved hydrophobic segments around the knotted region.
Collapse
Affiliation(s)
- Stefan Wallin
- Department of Chemistry & Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA
| | | | | |
Collapse
|
27
|
Wallin S, Davidsson J, Modin J, Hammarström L. Femtosecond Transient Absorption Anisotropy Study on [Ru(bpy)3]2 + and [Ru(bpy)(py)4]2 +. Ultrafast Interligand Randomization of the MLCT State. J Phys Chem A 2005. [DOI: 10.1021/jp054777w] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
28
|
Wallin S, Chan HS. A critical assessment of the topomer search model of protein folding using a continuum explicit-chain model with extensive conformational sampling. Protein Sci 2005; 14:1643-60. [PMID: 15930009 PMCID: PMC2253387 DOI: 10.1110/ps.041317705] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Recently, a series of closely related theoretical constructs termed the "topomer search model" (TSM) has been proposed for the folding mechanism of small, single-domain proteins. A basic assumption of the proposed scenarios is that the rate-limiting step in folding is an essentially unbiased, diffusive search for a conformational state called the native topomer defined by an overall native-like topological pattern. Successes in correlating TSM-predicted folding rates with that of real proteins have been interpreted as experimental support for the model. To better delineate the physics entailed, key TSM concepts are examined here using extensive Langevin dynamics simulations of continuum C(alpha) chain models. The theoretical native topomers of four experimentally well-studied two-state proteins are characterized. Consistent with the TSM perspective, we found that the sizes of the native topomers increase with experimental folding rate. However, a careful determination of the corresponding probabilities that the native topomers are populated during a random search fails to reproduce the previously predicted folding rates. Instead, our results indicate that an unbiased TSM search for the native topomer amounts to a Levinthal-like process that would take an impossibly long average time to complete. Furthermore, intraprotein contacts in all four native topomers considered exhibit no apparent correlation with the experimental phi-values determined from the folding kinetics of these proteins. Thus, the present findings suggest that certain basic, generic yet essential energetic features in protein folding are not accounted for by TSM scenarios to date.
Collapse
Affiliation(s)
- Stefan Wallin
- Department of Biochemistry, University of Toronto, 1 King's College Circle, Toronto, Ontario M5S 1A8, Canada
| | | |
Collapse
|
29
|
Abstract
Z(SPA-1) is an engineered protein that binds to its parent, the three-helix-bundle Z domain of staphylococcal protein A. Uncomplexed Z(SPA-1) shows a reduced helix content and a melting behavior that is less cooperative, compared with the wild-type Z domain. Here we show that the difference in folding behavior between these two sequences can be partly understood in terms of an off-lattice model with 5-6 atoms per amino acid and a minimalistic potential, in which folding is driven by backbone hydrogen bonding and effective hydrophobic attraction.
Collapse
Affiliation(s)
- Giorgio Favrin
- Complex Systems Division, Department of Theoretical Physics, Lund University, Lund, Sweden
| | | | | |
Collapse
|
30
|
Abstract
An atomic protein model with a minimalistic potential is developed and then tested on an alpha-helix and a beta-hairpin, using exactly the same parameters for both peptides. We find that melting curves for these sequences to a good approximation can be described by a simple two-state model, with parameters that are in reasonable quantitative agreement with experimental data. Despite the apparent two-state character of the melting curves, the energy distributions are found to lack a clear bimodal shape, which is discussed in some detail. We also perform a Monte Carlo-based kinetic study and find, in accord with experimental data, that the alpha-helix forms faster than the beta-hairpin.
Collapse
Affiliation(s)
- Anders Irbäck
- Complex Systems Division, Department of Theoretical Physics, Lund University, Lund, Sweden.
| | | | | | | |
Collapse
|
31
|
Abstract
We present a Monte Carlo study of a model protein with 54 amino acids that folds directly to its native three-helix-bundle state without forming any well-defined intermediate state. The free-energy barrier separating the native and unfolded states of this protein is found to be weak, even at the folding temperature. Nevertheless, we find that melting curves to a good approximation can be described in terms of a simple two-state system, and that the relaxation behavior is close to single exponential. The motion along individual reaction coordinates is roughly diffusive on timescales beyond the reconfiguration time for a single helix. A simple estimate based on diffusion in a square-well potential predicts the relaxation time within a factor of two.
Collapse
Affiliation(s)
- Giorgio Favrin
- Complex Systems Division, Department of Theoretical Physics, Lund University, Sölvegatan 14A, SE-223 62 Lund, Sweden
| | | | | | | |
Collapse
|
32
|
Abstract
There are many ways to define the distance between two protein structures, thus assessing their similarity. Here, we investigate and compare the properties of five different distance measures, including the standard root-mean-square deviation (cRMSD). The performance of these measures is studied from different perspectives with two different protein models, one continuous and the other discrete. Using the continuous model, we examine the correlation between energy and native distance, and the ability of the different measures to discriminate between the two possible topologies of a three-helix bundle. Using the discrete model, we perform fits to real protein structures by minimizing different distance measures. The properties of the fitted structures are found to depend strongly on the distance measure used and the scale considered. We find that the cRMSD measure very effectively describes long-range features but is less effective with short-range features, and it correlates weakly with energy. A stronger correlation with energy and a better description of short-range properties is obtained when we use measures based on intramolecular distances.
Collapse
Affiliation(s)
- Stefan Wallin
- Complex Systems Division, Department of Theoretical Physics, Lund University, Sölvegatan 14A, SE-223 62 Lund, Sweden.
| | | | | |
Collapse
|
33
|
Abstract
A reduced protein model with five to six atoms per amino acid and five amino acid types is developed and tested on a three-helix-bundle protein, a 46-amino acid fragment from staphylococcal protein A. The model does not rely on the widely used Go approximation, which ignores non-native interactions. We find that the collapse transition is considerably more abrupt for the protein A sequence than for random sequences with the same composition. The chain collapse is found to be at least as fast as helix formation. Energy minimization restricted to the thermodynamically favored topology gives a structure that has a root-mean-square deviation of 1.8 A from the native structure. The sequence-dependent part of our potential is pairwise additive. Our calculations suggest that fine-tuning this potential by parameter optimization is of limited use.
Collapse
Affiliation(s)
- Giorgio Favrin
- Department of Theoretical Physics, Complex Systems Division, Lund University, Lund, Sweden
| | | | | |
Collapse
|
34
|
Abstract
We study the thermodynamic behavior of a model protein with 54 amino acids that forms a three-helix bundle in its native state. The model contains three types of amino acids and five to six atoms per amino acid and has the Ramachandran torsional angles phi(i), psi(i) as its degrees of freedom. The force field is based on hydrogen bonds and effective hydrophobicity forces. For a suitable choice of the relative strength of these interactions, we find that the three-helix-bundle protein undergoes an abrupt folding transition from an expanded state to the native state. Also shown is that the corresponding one- and two-helix segments are less stable than the three-helix sequence.
Collapse
Affiliation(s)
- A Irbäck
- Complex Systems Division, Department of Theoretical Physics, Lund University, Sölvegatan 14A, S-223 62 Lund, Sweden.
| | | | | |
Collapse
|
35
|
Coughlin TA, Zuckerman S, Wallin S, Holahan J. A conflict of strategies: Medicaid managed care and Medicaid maximization. Health Serv Res 1999; 34:281-93. [PMID: 10199675 PMCID: PMC1089001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023] Open
Abstract
OBJECTIVE To examine the influence of state strategies aimed at increasing federal Medicaid matching dollars on the design of states' Medicaid managed care programs. STUDY DESIGN Data obtained from the 1996-1997 case studies of 13 states to examine how states have adapted the design of their Medicaid managed care programs in part because of maximization strategies, to accommodate the many roles and responsibilities that Medicaid has assumed over the years. PRINCIPAL FINDINGS Our study showed that as states made the shift to managed care, some found that the responsibilities undertaken in part through maximization strategies proved to be in conflict with their Medicaid managed care initiatives. Among other things, the study revealed that most states included provisions that preserved the health care safety net, such as adapting the managed care benefit package and promoting the participation of safety net providers in managed care programs. In addition, most of the study states continued to pay special subsidies to safety net providers, including hospitals and clinics. CONCLUSIONS States have made real progress in moving a large number of Medicaid beneficiaries into managed care. At the same time, many states have specially crafted their managed care programs to accommodate safety net providers and existing funding mechanisms. By making these adaptations states, in the long run, may compromise the central goals of managed care: controlling costs and improving Medicaid beneficiaries' access to and quality of care.
Collapse
|
36
|
Abstract
The spectrum of TaS between 4000 and 20 000 cm-1 has been recorded in emission from a microwave discharge with a resolution between 0.011 and 0.025 cm-1. Seventeen electronic transitions have been rotationally analyzed. Fifteen of these have the ground state, 2Delta, as the lower state and two of them are transitions between excited states. The ground state has been fitted to a Hund's case (a) Hamiltonian. Effective molecular constants have been determined for the excited states, which are mainly described as Hund's case (c). Perturbations that have been found in the excited states are discussed. Transitions between states that are connected neither to the ground state nor to any of the other 14 electronic states of this work have been found. No analysis is presented for these transitions, but some of their characteristic features are described. Copyright 1998 Academic Press.
Collapse
Affiliation(s)
- S Wallin
- Department of Physics, Stockholm University, Stockholm, S-11385, Sweden
| | | | | |
Collapse
|
37
|
Abstract
Three electronic transitions in the singlet manifold of the zirconium sulphide (ZrS) molecule have been rotationally analyzed. They are the B1Pi-X1Sigma+, C1Sigma+-X1Sigma+, and E1Sigma+-X1Sigma+ systems with (0,0) band heads at 924.60, 731.51, and 494.47 nm, respectively. The ground state X1Sigma+ has an equilibrium bond distance of 2.15661(4) Å. Perturbations in the B1Pi and C1Sigma+ states are discussed. Copyright 1998 Academic Press.
Collapse
Affiliation(s)
- J Jonsson
- Department of Physics, Stockholm University, Stockholm, S-11385, Sweden
| | | | | |
Collapse
|
38
|
Rowland FS, Blake DR, Larsen BR, Lindskog A, Peterson PJ, Williams WP, Wallington TJ, Pilling MJ, Carslaw N, Creasey DJ, Heard DE, Jacobs P, Lee J, Lewis AC, McQuaid JB, Stockwell WR, Frank H, Sacco P, Cocheo V, Lynge E, Andersen A, Nilsson R, Barlow L, Pukkala E, Nordlinder R, Boffetta P, Grandjean P, Heikkil P, Hürte LG, Jakobsson R, Lundberg I, Moen B, Partanen T, Riise T, Borowiak A, De Saeger E, Schnitzler KG, Gravenhorst G, Jacobi HW, Moelders S, Lammel G, Busch G, Beese FO, Dentener FJ, Feichter J, Fraedrich K, Roelofs GJ, Friedrich R, Reis S, Voehringer F, Simpson D, Moussiopoulos N, Sahm P, Tourlou PM, Salmons R, Papameletiou D, Maqueda JM, Suhr PB, Bell W, Paton-Walsh C, Woods PT, Partridge RH, Slemr J, Slemr F, Schmidbauer N, Ravishankara AR, Jenkin ME, de Leeuw G, van Eijk AM, Flossmann AI, Wobrock W, Mestayer PG, Tranchant B, Ljungström E, Karlsson R, Larsen SE, Roemer M, Builtjes PJ, Koffi B, Koffi EN, De Saeger E, Ro-Poulsen H, Mikkelsen TN, Hummelshøj P, Hovmand MF, Simoneit BR, van der Meulen A, Meyer MB, Berndt T, Böge O, Stratmann F, Cass GR, Harrison RM, Shi JP, Hoffmann T, Warscheid B, Bandur R, Marggraf U, Nigge W, Kamens R, Jang M, Strommen M, Chien CJ, Leach K, Ammann M, Kalberer M, Arens F, Lavanchy V, Gâggeler HW, Baltensperger U, Davies JA, Cox RA, Alonso SG, Pastor RP, Argüello GA, Willner H, Berndt T, Böge O, Bogillo VI, Pokrovskiy VA, Kuraev OV, Gozhyk PF, Bolzacchini E, Bruschi M, Fantucci P, Meinardi S, Orlandi M, Rindone B, Bolzacchini E, Bohn B, Rindone B, Bruschi M, Zetzsch C, Brussol C, Duane M, Larsen B, Carlier P, Kotzias D, Caracena AB, Aznar AM, Ferradás EG, Christensen CS, Skov H, Hummelshøj P, Jensen NO, Lohse C, Cocheo V, Sacco P, Chatzis C, Cocheo V, Sacco P, Boaretto C, Quaglio F, Zaratin L, Pagani D, Cocheo L, Cocheo V, Asnar AM, Baldan A, Ballesta PP, Boaretto C, Caracena AB, Ferradas EG, Gonzalez-Flesca N, Goelen E, Hansen AB, Sacco P, De Saeger E, Skov H, Consonni V, Gramatica P, Santagostino A, Galvani P, Bolzacchini E, Consonni V, Gramatica P, Todeschini R, Dippel G, Reinhardt H, Zellner R, Dämmer K, Bednarek G, Breil M, Zellner R, Febo A, Allegrini I, Giliberti C, Perrino C, Fogg PG, Geiger H, Barnes I, Becker KH, Maurer T, Geyskens F, Bormans R, Lambrechts M, Goelen E, Giese M, Frank H, Glasius M, Hornung P, Jacobsen JK, Klausen HS, Klitgaard KC, Møller CK, Petersen AP, Petersen LS, Wessel S, Hansen TS, Lohse C, Boaretto E, Heinemeier J, Glasius M, Di Bella D, Lahaniati M, Calogirou A, Jensen NR, Hjorth J, Kotzias D, Larsen BR, Gonzalez-Flesca N, Cicolella A, Bates M, Bastin E, Gurbanov MA, Akhmedly KM, Balayev VS, Haselmann KF, Ketola R, Laturnus F, Lauritsen FR, Grøn C, Herrmann H, Ervens B, Reese A, Umschlag T, Wicktor F, Zellner R, Herrmann H, Umschlag T, Müller K, Bolzacchini E, Meinardi S, Rindone B, Jenkin ME, Hayman GD, Jensen NO, Courtney M, Hummelshøj P, Christensen CS, Larsen BR, Johnson MS, Hegelund F, Nelander B, Kirchner F, Klotz B, Barnes I, Sørensen S, Becker KH, Etzkorn T, Platt U, Wirtz K, Martín-Reviejo M, Laturnus F, Martinez E, Cabañas B, Aranda A, Martín P, Salgado S, Rodriguez D, Masclet P, Jaffrezo JL, Hillamo R, Mellouki A, Le Calvé S, Le Bras G, Moriarty J, O'Donnell S, Wenger J, Sidebottom H, Mingarrol MT, Cosin S, Pastor RP, Alonso SG, Sanz MJ, Bravo I, Gonzalez D, Pérez MA, Mustafaev I, Mammadova S, Noda J, Hallquist M, Langer S, Ljungström E, Nohara K, Kutsuna S, Ibusuki T, Oehme M, Kölliker S, Brombacher S, Merz L, Pastor RP, Alonso SG, Cabezas AQ, Peeters J, Vereecken L, El Yazal J, Pfeffer HU, Breuer L, Platz J, Nielsen OJ, Sehested J, Wallington TJ, Ball JC, Hurley MD, Straccia AM, Schneider WF, Pérez-Casany MP, Nebot-Gil I, Sánchez-Marín J, Putz E, Folberth G, Pfister G, Weissflog L, Elansky NP, Sørensen S, Barnes I, Becker KH, Shao M, Heiden AC, Kley D, Rockel P, Wildt J, Silva GV, Vasconcelos MT, Fernandes EO, Santos AM, Skov H, Hansen A, Løfstrøm P, Lorenzen G, Stabel JR, Wolkoff P, Pedersen T, Strom AB, Skov H, Hertel O, Jensen FP, Hjorth J, Galle B, Wallin S, Theloke J, Libuda HG, Zabel F, Touaty M, Bonsang B, Ullerstam M, Langer S, Ljungström E, Wenger J, Bonard A, Manning M, Nolan S, O'Sullivan N, Sidebottom H, Wenger J, Collins E, Moriarty J, O'Donnell S, Sidebottom H, Wenger J, Collins E, Moriarty J, O'Donnell S, Sidebottom H, Wenger J, Sidebottom H, Chadwick P, O'Leary B, Treacy J, Wolkoff P, Clausen PA, Wilkins CK, Hougaard KS, Nielsen GD, Zilinskis V, Jansons G, Peksens A, Lazdins A, Arinci YV, Erdöl N, Ekinci E, Okutan H, Manlafalioglu I, Bakeas EB, Siskos PA, Viras LG, Smirnioudi VN, Bottenheim JW, Biesenthal T, Gong W, Makar P, Delmas V, Menard T, Tatry V, Moussafir J, Thomas D, Coppalle A, Ellermann T, Hertel O, Skov H, Frohn L, Manscher OH, Friis J, Girgzdiene R, Girgzdys A, Gurevich NA, Gårdfeldt K, Langer S, Hermans C, Vandaele AC, Carleer M, Fally S, Colin R, Bernath PF, Jenouvrier A, Coquart B, Mérienne MF, Hertel O, Frohn L, Skov H, Ellermann T, Huntrieser H, Schlager H, Feigl C, Kemp K, Palmgren F, Kiilsholm S, Rasmussen A, Sørensen JH, Klemm O, Lange H, Larsen RW, Larsen NW, Nicolaisen F, Sørensen GO, Beukes JA, Larsen PB, Jensen SS, Fenger J, de Leeuw G, Kunz G, Cohen L, Schlünzen H, Muller F, Schulz M, Tamm S, Geernaert G, Hertel O, Pedersen B, Geernaert LL, Lund S, Vignati E, Jickells T, Spokes L, Matei C, Jinga OA, Jinga DC, Moliner R, Braekman-Danheux C, Fontana A, Suelves I, Thieman T, Vassilev S, Skov H, Hertel O, Zlatev Z, Brandt J, Bastrup-Birk A, Ellermann T, Frohn L, Vandaele AC, Hermans C, Carleer M, Tsouli A, Colin R, Windsperger AM, Turi K, Dworak O, Zellweger C, Weingartner E, Rüttimann R, Hofer P, Baltensperger U, Ziv A, Iakovleva E, Palmgren F, Berkovicz R, Skov H, Alastuey A, Querol X, Chaves A, Lopez-Soler A, Ruiz C, Andrees JM, Allegrini I, Febo A, Giusto M, Angeloni M, Di Filippo P, D'Innocenzio F, Lepore L, Marconi A, Arshinov MY, Belan BD, Davydov DK, Kovaleskii VK, Plotinov AP, Pokrovskii EV, Sklyadneva TK, Tolmachev GN, Arshinov MY, Belan BD, Sklyadneva TK, Behnke W, Elend M, Krüger U, Zetzsch C, Belan BD, Arshinov MY, Davydov DK, Kovalevskii VK, Plotnikov AP, Pokrovskii EV, Rasskazchikova TM, Sklyadneva TK, Tolmachev GN, Belan BD, Arshinov MY, Simonenkov DV, Tolmachev GN, Bilde M, Aker PM, Börensen C, Kirchner U, Scheer V, Vogt R, Ellermann T, Geernaert LL, Pryor SC, Barthelmie RJ, Feilberg A, Nielsen T, Kamens RM, Freitas MC, Marques AP, Reis MA, Alves LC, Ilyinskikh NN, Ilyinskikh IN, Ilyinskikh EN, Johansen K, Stavnsbjerg P, Gabrielsson P, Bak F, Andersen E, Autrup H, Kamens R, Jang M, Strommen M, Leach K, Kirchner U, Scheer V, Börensen C, Vogt R, Igor K, Svjatoslav G, Anatoliy B, Komov IL, Istchenko AA, Lourenço MG, Mactavish D, Sirois A, Masclet P, Jaffrezo JL, van der Meulen A, Milukaite A, Morkunas V, Jurgutis P, Mikelinskiene A, Nielsen T, Feilberg A, Binderup ML, Pineda M, Palacios JM, Garcia E, Cilleruelo C, Moliner R, Popovitcheva OB, Trukhin ME, Persiantseva NM, Buriko Y, Starik AM, Demirdjian B, Suzanne J, Probst TU, Rietz B, Alfassi ZB, Pokrovskiy VA, Zenobi R, Bogatyr'ov VM, Gun'ko VM, Querol X, Alastuey A, Lopez-Soler A, Mantilla E, Plana F, Artiño B, Rauterberg-Wulff A, Israël GW, Rocha TA, Duarte AC, Röhrl A, Lammel G, Spindler G, Müller K, Herrmann H, Strommen MR, Vignati E, de Leeuw G, Berkowicz R. Abstracts of the 6th FECS Conference 1998 Lectures. Environ Sci Pollut Res Int 1998; 5:119-96. [PMID: 19002640 DOI: 10.1007/bf02986409] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Affiliation(s)
- F S Rowland
- Department of Chemistry, University of California, Irvine, 92697, California, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
39
|
Affiliation(s)
- S. Wallin
- Department of Physics, Stockholm University, Box 6730 S‐11385 Stockholm, Sweden
| | - R. Koivisto
- Department of Physics, Stockholm University, Box 6730 S‐11385 Stockholm, Sweden
| | - O. Launila
- Department of Physics, Stockholm University, Box 6730 S‐11385 Stockholm, Sweden
| |
Collapse
|
40
|
Wallin S, Walum E. Effects of Carbon Tetrachloride on Perfused Cultures of Hepatic and Neuronal Cells. Altern Lab Anim 1992. [DOI: 10.1177/026119299202000210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Cultured hepatocytes and hemisphere neurons from chick embryos and mouse neuroblastoma cells were exposed to carbon tetrachloride (CC14; 0, 1, 2, 3 and 4mM) for 1 hour, using a perfusion system developed for studying the effects of volatile substances. In the perfused cultures, three parameters were compared: lipid peroxidation, membrane integrity and cellular respiration. In addition, cytochrome C oxidase activity was determined after incubation of cell homogenates with CC14. A concentration-dependent increase in lipid peroxidation and membrane permeability was found in the neuroblastoma cells. The hepatocytes responded to a lesser extent with respect to membrane permeability and their lipid peroxidation did not differ from that of controls. The hepatocytes responded with a 35% decrease in respiration when exposed to 3mM CC14, and a 20% decrease in cytochrome C oxidase activity after treatment with 1.5mM CCl4. In the neuronal cells, much smaller decreases in respiration were found and their cytochrome C oxidase activity remained unaffected. These results are very similar to those obtained after incubation in a closed chamber system. However, the perfused cells were found to be less sensitive to CCl4than cells exposed under static conditions.
Collapse
Affiliation(s)
- Stefan Wallin
- Unit of Neurochemistry and Neurotoxicology, University of Stockholm, S-106 91 Stockholm, Sweden
| | - Erik Walum
- Unit of Neurochemistry and Neurotoxicology, University of Stockholm, S-106 91 Stockholm, Sweden
| |
Collapse
|
41
|
Wallin S, Orrevall Y. [Nurse consultant--a link between hospital care and primary care]. Vardfacket 1990; 14:XVI-XVIII. [PMID: 2382482] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
|
42
|
Lindemalm C, Bergström M, Häggmark C, Mattsson A, Rotstein S, Wallin S, Wikström E, Danhardt L, Trampe E, Edberg L. [Oncologic consultations in the Stockholm-Gotland region are a well-functioning model]. Lakartidningen 1989; 86:2961-3. [PMID: 2796480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
|
43
|
Abstract
In organized health care, primary care is the first level. It is characterized by the wide span of health problems managed as well as remote location from traditional medical information and knowledge sources. The LIMEDS project has formulated the special requirements for integrated knowledge and data base management in primary care. This paper presents
Gösta's book
, a hypertext knowledge base implemented in LINCKS, an object oriented, networked database system. Firstly, aspects which make integrated hypermedia systems particularly suitable for application in primary health care are explored. We then describe the hypertext knowledge base, consisting of 500 basic text objects and 3000 links, and current implementations using the NODE data model. NODE is implemented on a SUN III fileserver, and the user interface for the hypertext context on Apple Macintosh (TM). Combination of design methods towards a parallel means-ends strategy was found to be necessary to achieve
Gösta's book
. Design groups need to be composed of computer science, medical, psychological and organizational competences.
Collapse
Affiliation(s)
- T. Timpka
- Department of Computer Science and Department of Community Medicine Linköping University, 581 83 Linköping, Sweden
| | - L. Padgham
- Department of Computer Science, Linköping University, 581 83 Linköping, Sweden
| | - P. Hedblom
- Department of Computer Science, Linköping University, 581 83 Linköping, Sweden
| | - S. Wallin
- Department of Computer Science, Linköping University, 581 83 Linköping, Sweden
| | - T. Tibblin
- Department of Family Medicine, Uppsala University
| |
Collapse
|
44
|
Odland L, Wallin S, Walum E. Lipid peroxidation and activities of tyrosine aminotransferase and glutamine synthetase in hepatoma and glioma cells grown in bovine colostrum-supplemented medium. In Vitro Cell Dev Biol 1986; 22:259-62. [PMID: 2872199 DOI: 10.1007/bf02621228] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The growth stimulating properties of bovine serum and colostrum were compared in rat hepatoma (HTC) and glioma (C6) cell cultures. A colostrum concentration of 2% was optimal for HTC cells, which then reached a terminal density 40% of that in serum-supplemented medium. The corresponding figures for C6 cells were 10 and 81%, respectively. After 4 d in culture, levels of lipid hydroperoxides were measured and compared. Highest levels of lipid hydroperoxides were found in HTC and C6 cells grown in unsupplemented medium. HTC and C6 cells grown in serum supplemented medium contained levels of 52 and 64%, respectively, of that in unsupplemented medium. The corresponding levels for cells grown in presence of colostrum were 40% for HTC and 44% for C6 cells. To obtain information on any functional alterations in the cells due to the presence of colostrum the induction of tyrosine aminotransferase (EC 2.6.1.5) and glutamine synthetase (EC 6.3.1.2) by dexamethasone was studied. Although colostrum seemed to increase the basal activities of the enzymes, no significant effects on the degree of induction could be detected.
Collapse
|
45
|
Edner H, Sunesson A, Svanberg S, Unéus L, Wallin S. Differential optical absorption spectroscopy system used for atmospheric mercury monitoring. Appl Opt 1986; 25:403-409. [PMID: 18231190 DOI: 10.1364/ao.25.000403] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
A high-resolution differential optical absorption spectroscopy (DOAS) system for long-path atmospheric pollution monitoring is described. The system, consisting of a broadband lamp and a dispersive, fast-scanning optical receiver, separated by a few kilometers, was used in measurements of different pollutants, highlighted by the monitoring of the local concentration of atomic mercury. Mercury levels in the ppt (1:10(12)) range were assessed by comparisons with laboratory measurements.
Collapse
Affiliation(s)
- H Edner
- Lund Institute of Technology, Physics Department, P.O. Box 118, S-221 00 Lund, Sweden
| | | | | | | | | |
Collapse
|
46
|
Aldén M, Edner H, Wallin S. Simultaneous spatially resolved NO and NO(2) measurements using one- and two-photon laser-induced fluorescence. Opt Lett 1985; 10:529-531. [PMID: 19730474 DOI: 10.1364/ol.10.000529] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We demonstrate how spatially resolved distributions of NO and NO(2) can be simultaneously detected by using a single laser pulse at 452 nm. The laser-induced fluorescence from NO was achieved by a two-photon transition in the gamma band at 226 nm followed by UV detection, whereas NO(2) was detected by a one-photon transition followed by Stokes fluorescence.
Collapse
|
47
|
|
48
|
Wallin S. [Nurses' own cancer consultation. Interview by Inger Lernevall]. Vardfacket 1985; 9:24-5. [PMID: 3852606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
|
49
|
Wallin S. [Stig Wallin, regional SHSTF's representative--great risk that professional work will formalize for many]. Vardfacket 1985; 9:22-3. [PMID: 3852592] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
|
50
|
Aldén M, Hertz HM, Svanberg S, Wallin S. Imaging laser-induced fluorescence of oxygen atoms in a flame. Appl Opt 1984; 23:3255-3257. [PMID: 20431648 DOI: 10.1364/ao.23.003255] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
|