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Yang HH, Wang X, Li S, Liu Y, Akbar R, Fan GC. Lipocalin family proteins and their diverse roles in cardiovascular disease. Pharmacol Ther 2023; 244:108385. [PMID: 36966973 PMCID: PMC10079643 DOI: 10.1016/j.pharmthera.2023.108385] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2023] [Revised: 03/01/2023] [Accepted: 03/13/2023] [Indexed: 04/03/2023]
Abstract
The lipocalin (LCN) family members, a group of small extracellular proteins with 160-180 amino acids in length, can be detected in all kingdoms of life from bacteria to human beings. They are characterized by low similarity of amino acid sequence but highly conserved tertiary structures with an eight-stranded antiparallel β-barrel which forms a cup-shaped ligand binding pocket. In addition to bind small hydrophobic ligands (i.e., fatty acids, odorants, retinoids, and steroids) and transport them to specific cells, lipocalins (LCNs) can interact with specific cell membrane receptors to activate their downstream signaling pathways, and with soluble macromolecules to form the complex. Consequently, LCNs exhibit great functional diversity. Accumulating evidence has demonstrated that LCN family proteins exert multiple layers of function in the regulation of many physiological processes and human diseases (i.e., cancers, immune disorders, metabolic disease, neurological/psychiatric disorders, and cardiovascular disease). In this review, we firstly introduce the structural and sequence properties of LCNs. Next, six LCNs including apolipoprotein D (ApoD), ApoM, lipocalin 2 (LCN2), LCN10, retinol-binding protein 4 (RBP4), and Lipocalin-type prostaglandin D synthase (L-PGDS) which have been characterized so far are highlighted for their diagnostic/prognostic values and their potential effects on coronary artery disease and myocardial infarction injury. The roles of these 6 LCNs in cardiac hypertrophy, heart failure, diabetes-induced cardiac disorder, and septic cardiomyopathy are also summarized. Finally, their therapeutic potential for cardiovascular disease is discussed in each section.
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Affiliation(s)
- Hui-Hui Yang
- Department of Pharmacology and Systems Physiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA
| | - Xiaohong Wang
- Department of Pharmacology and Systems Physiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA
| | - Siru Li
- Department of Pharmacology and Systems Physiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA
| | - Yueying Liu
- Department of Pharmacology and Systems Physiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA
| | - Rubab Akbar
- Department of Pharmacology and Systems Physiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA
| | - Guo-Chang Fan
- Department of Pharmacology and Systems Physiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA.
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2
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Gasymov OK, Abduragimov AR, Glasgow BJ. Exploring protein solution structure: Second moments of fluorescent spectra report heterogeneity of tryptophan rotamers. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2015; 150:909-920. [PMID: 26119357 PMCID: PMC4550534 DOI: 10.1016/j.saa.2015.06.043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Revised: 03/11/2015] [Accepted: 06/15/2015] [Indexed: 06/04/2023]
Abstract
Trp fluorescent spectra appear as a log-normal function but are usually analyzed with λmax, full width at half maximum, and the first moment of incomplete spectra. Log-normal analyses have successfully separated fluorescence contributions from some multi-Trp proteins but deviations were observed in single Trp proteins. The possibility that disparate rotamer environments might account for these deviations was explored by moment spectral analysis of single Trp mutants spanning the sequence of tear lipocalin as a model. The analysis required full width Trp spectra. Composite spectra were constructed using log-normal analysis to derive the inaccessible blue edge, and the experimentally obtained spectra for the remainder. First moments of the composite spectra reflected the site-resolved secondary structure. Second moments were most sensitive for spectral deviations. A novel parameter, derived from the difference of the second moments of composite and simulated log-normal spectra correlated with known multiple heterogeneous rotamer conformations. Buried and restricted side chains showed the most heterogeneity. Analyses applied to other proteins further validated the method. The rotamer heterogeneity values could be rationalized by known conformational properties of Trp residues and the distribution of nearby charged groups according to the internal Stark effect. Spectral heterogeneity fits the rotamer model but does not preclude other contributing factors. Spectral moment analysis of full width Trp emission spectra is accessible to most laboratories. The calculations are informative of protein structure and can be adapted to study dynamic processes.
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Affiliation(s)
- Oktay K Gasymov
- Departments of Pathology and Ophthalmology and Jules Stein Eye Institute, University California at Los Angeles, CA 90095, United States.
| | - Adil R Abduragimov
- Departments of Pathology and Ophthalmology and Jules Stein Eye Institute, University California at Los Angeles, CA 90095, United States.
| | - Ben J Glasgow
- Departments of Pathology and Ophthalmology and Jules Stein Eye Institute, University California at Los Angeles, CA 90095, United States.
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3
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Gasymov OK, Abduragimov AR, Glasgow BJ. Double tryptophan exciton probe to gauge proximal side chains in proteins: augmentation at low temperature. J Phys Chem B 2015; 119:3962-8. [PMID: 25693116 DOI: 10.1021/jp512864s] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The circular dichroic (CD) exciton couplet between tryptophans and/or tyrosines offers the potential to probe distances within 10 Å in proteins. The exciton effect has been used with native chromophores in critical positions in a few proteins. Here, site-directed mutagenesis created double tryptophan probes for key sites of a protein (tear lipocalin). For tear lipocalin, the crystal and solution structures are concordant in both apo- and holo-forms. Double tryptophan substitutions were performed at sites that could probe conformation and were likely within 10 Å. Far-UV CD spectra of double Trp mutants were performed with controls that had noninteracting substituted tryptophans. Low temperature (77 K) was tested for augmentation of the exciton signal. Exciton coupling appeared with tryptophan substitutions at positions within loop A-B (28 and 31, 33), between loop A-B (28) and strand G (103 and 105), as well as between the strands B (35) and C (56). The CD exciton couplet signals were amplified 3-5-fold at 77 K. The results were concordant with close distances in crystal and solution structures. The exciton couplets had functional significance and correctly assigned the holo-conformation. The methodology creates an effective probe to identify proximal amino acids in a variety of motifs.
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Affiliation(s)
- Oktay K Gasymov
- Departments of Pathology and Ophthalmology and Jules Stein Eye Institute, University California at Los Angeles , Los Angeles, California 90095, United States
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Staudinger T, Redl B, Glasgow BJ. Antibacterial activity of rifamycins for M. smegmatis with comparison of oxidation and binding to tear lipocalin. BIOCHIMICA ET BIOPHYSICA ACTA 2014; 1844:750-8. [PMID: 24530503 PMCID: PMC3992280 DOI: 10.1016/j.bbapap.2014.02.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2013] [Revised: 01/28/2014] [Accepted: 02/03/2014] [Indexed: 11/19/2022]
Abstract
A mutant of Mycobacterium smegmatis is a potential class I model substitute for Mycobacterium tuberculosis. Because not all of the rifamycins have been tested in this organism, we determined bactericidal profiles for the 6 major rifamycin derivatives. The profiles closely mirrored those established for M. tuberculosis. Rifalazil was confirmed to be the most potent rifamycin. Because the tuberculous granuloma presents a harshly oxidizing environment we explored the effects of oxidation on rifamycins. Mass spectrometry confirmed that three of the six major rifamycins showed autoxidation in the presence of trace metals. Oxidation could be monitored by distinctive changes including isosbestic points in the ultraviolet-visible spectrum. Oxidation of rifamycins abrogated anti-mycobacterial activity in M. smegmatis. Protection from autoxidation was conferred by binding susceptible rifamycins to tear lipocalin, a promiscuous lipophilic protein. Rifalazil was not susceptible to autoxidation but was insoluble in aqueous solution. Solubility was enhanced when complexed to tear lipocalin and was accompanied by a spectral red shift. The positive solvatochromism was consistent with robust molecular interaction and binding. Other rifamycins also formed a complex with lipocalin, albeit to a lesser extent. Protection from oxidation and enhancement of solubility with protein binding may have implications for delivery of select rifamycin derivatives.
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Affiliation(s)
- Tamara Staudinger
- Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, 100 Stein Plaza, Rm. B-279, Los Angeles, CA 90095, USA; Department of Pathology and Laboratory Medicine, Jules Stein Eye Institute, University of California, Los Angeles, 100 Stein Plaza, Rm. B-279, Los Angeles, CA 90095, USA; Division of Molecular Biology, Biocenter, Innsbruck Medical University, Innrain 80-82, A-6020 Innsbruck, Austria
| | - Bernhard Redl
- Division of Molecular Biology, Biocenter, Innsbruck Medical University, Innrain 80-82, A-6020 Innsbruck, Austria
| | - Ben J Glasgow
- Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, 100 Stein Plaza, Rm. B-279, Los Angeles, CA 90095, USA; Department of Pathology and Laboratory Medicine, Jules Stein Eye Institute, University of California, Los Angeles, 100 Stein Plaza, Rm. B-279, Los Angeles, CA 90095, USA.
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Gasymov OK, Abduragimov AR, Glasgow BJ. Probing tertiary structure of proteins using single Trp mutations with circular dichroism at low temperature. J Phys Chem B 2014; 118:986-95. [PMID: 24404774 PMCID: PMC3983331 DOI: 10.1021/jp4120145] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
![]()
Trp is the most spectroscopically
informative aromatic amino acid
of proteins. However, the near-UV circular dichroism (CD) spectrum
of Trp is complicated because the intensity and sign of 1La and 1Lb bands vary independently.
To resolve vibronic structure and gain site-specific information from
complex spectra, deconvolution was combined with cooling and site-directed
tryptophan substitution. Low temperature near-UV CD was used to probe
the local tertiary structure of a loop and α-helix in tear lipocalin.
Upon cooling, the enhancement of the intensities of the near-UV CD
was not uniform, but depends on the position of Trp in the protein
structure. The most enhanced 1Lb band was observed
for Trp at position 124 in the α-helix segment matching the
known increased conformational mobility during ligand binding. Some
aspects of the CD spectra of W28 and W130 were successfully linked
to specific rotamers of Trp previously obtained from fluorescence
lifetime measurements. The discussion was based on a framework that
the magnitude of the energy differences in local conformations governs
the changes in the CD intensities at low temperature. The Trp CD spectral
classification of Strickland was modified to facilitate the recognition
of pseudo peaks. Near-UV CD spectra harbor abundant information about
the conformation of proteins that site directed Trp CD can report.
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Affiliation(s)
- Oktay K Gasymov
- Departments of Pathology and Ophthalmology and Jules Stein Eye Institute, University California at Los Angeles , California 90095, United States
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Gasymov OK, Abduragimov AR, Glasgow BJ. Effect of short- and long-range interactions on trp rotamer populations determined by site-directed tryptophan fluorescence of tear lipocalin. PLoS One 2013; 8:e78754. [PMID: 24205305 PMCID: PMC3810256 DOI: 10.1371/journal.pone.0078754] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Accepted: 09/20/2013] [Indexed: 11/25/2022] Open
Abstract
In the lipocalin family, the conserved interaction between the main α-helix and the β-strand H is an ideal model to study protein side chain dynamics. Site-directed tryptophan fluorescence (SDTF) has successfully elucidated tryptophan rotamers at positions along the main alpha helical segment of tear lipocalin (TL). The rotamers assigned by fluorescent lifetimes of Trp residues corroborate the restriction expected based on secondary structure. Steric conflict constrains Trp residues to two (t, g−) of three possible χ1 (t, g−, g+) canonical rotamers. In this study, investigation focused on the interplay between rotamers for a single amino acid position, Trp 130 on the α-helix and amino acids Val 113 and Leu 115 on the H strand, i.e. long range interactions. Trp130 was substituted for Phe by point mutation (F130W). Mutations at positions 113 and 115 with combinations of Gly, Ala, Phe residues alter the rotamer distribution of Trp130. Mutations, which do not distort local structure, retain two rotamers (two lifetimes) populated in varying proportions. Replacement of either long range partner with a small amino acid, V113A or L115A, eliminates the dominance of the t rotamer. However, a mutation that distorts local structure around Trp130 adds a third fluorescence lifetime component. The results indicate that the energetics of long-range interactions with Trp 130 further tune rotamer populations. Diminished interactions, evident in W130G113A115, result in about a 22% increase of α-helix content. The data support a hierarchic model of protein folding. Initially the secondary structure is formed by short-range interactions. TL has non-native α-helix intermediates at this stage. Then, the long-range interactions produce the native fold, in which TL shows α-helix to β-sheet transitions. The SDTF method is a valuable tool to assess long-range interaction energies through rotamer distribution as well as the characterization of low-populated rotameric states of functionally important excited protein states.
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Affiliation(s)
- Oktay K. Gasymov
- Departments of Pathology and Laboratory Medicine and Ophthalmology and Jules Stein Eye Institute, University of California Los Angeles, Los Angeles, California, United States of America
- * E-mail: (OG); (BG)
| | - Adil R. Abduragimov
- Departments of Pathology and Laboratory Medicine and Ophthalmology and Jules Stein Eye Institute, University of California Los Angeles, Los Angeles, California, United States of America
| | - Ben J. Glasgow
- Departments of Pathology and Laboratory Medicine and Ophthalmology and Jules Stein Eye Institute, University of California Los Angeles, Los Angeles, California, United States of America
- * E-mail: (OG); (BG)
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Gasymov OK, Abduragimov AR, Glasgow BJ. A simple model-free method for direct assessment of fluorescent ligand binding by linear spectral summation. J Fluoresc 2013; 24:231-8. [PMID: 24043458 DOI: 10.1007/s10895-013-1290-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Accepted: 08/21/2013] [Indexed: 10/26/2022]
Abstract
Fluorescent tagged ligands are commonly used to determine binding to proteins. However, bound and free ligand concentrations are not directly determined. Instead the response in a fluorescent ligand titration experiment is considered to be proportional to the extent of binding and, therefore, the maximum value of binding is scaled to the total protein concentration. Here, a simple model-free method is presented to be performed in two steps. In the first step, normalized bound and free spectra of the ligand are determined. In the second step, these spectra are used to fit composite spectra as the sum of individual components or linear spectral summation. Using linear spectral summation, free and bound 1-Anilinonaphthalene-8-Sulfonic Acid (ANS) fluorescent ligand concentrations are directly calculated to determine ANS binding to tear lipocalin (TL), an archetypical ligand binding protein. Error analysis shows that the parameters that determine bound and free ligand concentrations were recovered with high certainty. The linear spectral summation method is feasible when fluorescence intensity is accompanied by a spectral shift upon protein binding. Computer simulations of the experiments of ANS binding to TL indicate that the method is feasible when the fluorescence spectral shift between bound and free forms of the ligand is just 8 nm. Ligands tagged with environmentally sensitive fluorescent dyes, e.g., dansyl chromophore, are particularly suitable for this method.
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Affiliation(s)
- Oktay K Gasymov
- Departments of Ophthalmology, Pathology and Laboratory Medicine, Jules Stein Eye Institute, University of California at Los Angeles, Los Angeles, CA, 90095, USA,
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8
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Gasymov OK, Abduragimov AR, Glasgow BJ. Tryptophan rotamer distribution revealed for the α-helix in tear lipocalin by site-directed tryptophan fluorescence. J Phys Chem B 2012; 116:13381-8. [PMID: 23088798 DOI: 10.1021/jp309318r] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Rotamer libraries are a valuable tool for protein structure determination, modeling, and design. Site-directed tryptophan fluorescence (SDTF) was used in combination with the rotamer model for the fluorescence intensity decays to solve α-helical conformations of proteins in solution. Single Trp mutations located in an α-helical segment of human tear lipocalin were explored for structure assignment. Along with fluorescence λ(max) values, the rotamer model assignment of fluorescence lifetimes fits the backbone conformation. Typically, Trp fluorescence in proteins shows three lifetimes. However, for the α-helix, two lifetimes assigned to t and g(-) rotamers were satisfactory to describe Trp fluorescence intensity decays. The g(+) rotamer is not feasible in the α-helix due to steric restriction. Trp rotamer distributions obtained by fluorescence were compared with the rotamer library derived from X-ray crystallography data of proteins. The Trp rotamer distributions vary for solvent exposed and buried (tertiary interaction) sites. A new strategy using the rotamer distribution with SDTF (RD-SDTF) removes the limitation of regular SDTF and other labeling techniques, in which site-specific differences, e.g., accessibility, are presumed. The RD-SDTF technique does not rely on environmental differences of side chains and is able to detect α-helical structure where all side chains are exposed to solvent. Potentially, this technique is applicable to various proteins including membrane proteins, which are rich in α-helix motif.
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Affiliation(s)
- Oktay K Gasymov
- Department of Pathology and Jules Stein Eye Institute, University California at Los Angeles, Los Angeles, California 90095, USA.
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Gasymov OK, Abduragimov AR, Glasgow BJ. Cation-π interactions in lipocalins: structural and functional implications. Biochemistry 2012; 51:2991-3002. [PMID: 22439821 DOI: 10.1021/bi3002902] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The cation-π interaction impacts protein folding, structural stability, specificity, and molecular recognition. Cation-π interactions have been overlooked in the lipocalin family. To fill this gap, these interactions were analyzed in the 113 crystal and solution structures from the lipocalin family. The cation-π interactions link previously identified structurally conserved regions and reveal new motifs, which are beyond the reach of a sequence alignment algorithm. Functional and structural significance of the interactions were tested experimentally in human tear lipocalin (TL). TL, a prominent and promiscuous lipocalin, has a key role in lipid binding at the ocular surface. Ligand binding modulation through the loop AB at the "open" end of the barrel has been erroneously attributed solely to electrostatic interactions. Data revealed that the interloop cation-π interaction in the pair Phe28-Lys108 contributes significantly to stabilize the holo-conformation of the loop AB. Numerous energetically significant and conserved cation-π interactions were uncovered in TL and throughout the lipocalin family. Cation-π interactions, such as the highly conserved Trp17-Arg118 pair in TL, were educed in low temperature experiments of mutants with Trp to Tyr substitutions.
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Affiliation(s)
- Oktay K Gasymov
- Department of Pathology and Jules Stein Eye Institute, University California at Los Angeles, California 90095, USA.
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Gasymov OK, Abduragimov AR, Glasgow BJ. The conserved disulfide bond of human tear lipocalin modulates conformation and lipid binding in a ligand selective manner. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1814:671-83. [PMID: 21466861 DOI: 10.1016/j.bbapap.2011.03.017] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2010] [Revised: 02/28/2011] [Accepted: 03/29/2011] [Indexed: 11/26/2022]
Abstract
The primary aim of this study is the elucidation of the mechanism of disulfide induced alteration of ligand binding in human tear lipocalin (TL). Disulfide bonds may act as dynamic scaffolds to regulate conformational changes that alter protein function including receptor-ligand interactions. A single disulfide bond, (Cys61-Cys153), exists in TL that is highly conserved in the lipocalin superfamily. Circular dichroism and fluorescence spectroscopies were applied to investigate the mechanism by which disulfide bond removal effects protein stability, dynamics and ligand binding properties. Although the secondary structure is not altered by disulfide elimination, TL shows decreased stability against urea denaturation. Free energy change (ΔG(0)) decreases from 4.9±0.2 to 2.1±0.3kcal/mol with removal of the disulfide bond. Furthermore, ligand binding properties of TL without the disulfide vary according to the type of ligand. The binding of a bulky ligand, NBD-cholesterol, has a decreased time constant (from 11.8±0.2 to 3.3s). In contrast, the NBD-labeled phospholipid shows a moderate decrease in the time constant for binding, from 33.2±0.2 to 22.2±0.4s. FRET experiments indicate that the hairpin CD is directly involved in modulation of both ligand binding and flexibility of TL. In TL complexed with palmitic acid (PA-TL), the distance between the residues 62 of strand D and 81 of loop EF is decreased by disulfide bond reduction. Consequently, removal of the disulfide bond boosts flexibility of the protein to reach a CD-EF loop distance (24.3Å, between residues 62 and 81), which is not accessible for the protein with an intact disulfide bond (26.2Å). The results suggest that enhanced flexibility of the protein promotes a faster accommodation of the ligand inside the cavity and an energetically favorable ligand-protein complex.
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Affiliation(s)
- Oktay K Gasymov
- Department of Pathology, University of California, Los Angeles, USA.
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Gasymov OK, Abduragimov AR, Glasgow BJ. Excited protein states of human tear lipocalin for low- and high-affinity ligand binding revealed by functional AB loop motion. Biophys Chem 2010; 149:47-57. [PMID: 20439130 DOI: 10.1016/j.bpc.2010.03.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2010] [Revised: 03/22/2010] [Accepted: 03/28/2010] [Indexed: 10/19/2022]
Abstract
Human tear lipocalin (TL), a prominent member of lipocalin family, exhibits functional and structural promiscuity. The plasticity of loop regions modulates entry to the ligand pocket at the "open" end of the eight-stranded beta-barrel. Site-directed multi-distance measurements using fluorescence resonance energy transfer between functional loops register two excited protein states for low- and high-affinity ligand binding. At low pH, the longest loop AB adopts the conformation of the low-affinity excited protein state that matches the crystal structure of holo-TL at pH 8. A "crankshaft" like movement is detected for the loop AB in a low pH transition. At pH 7.3 the holo-protein assumes a high-affinity excited protein state, in which the loop AB is more compact (RMS=3.1A). In the apo-holo transition, the reporter Trp 28 moves about 4.5A that reflects a decrease in distance between Glu27 and Lys108. This interaction fixes the loop AB conformation for the high-affinity mode. No such movement is detected at low pH, where Glu27 is protonated. Data strongly indicate that the protonation state of Glu27 modulates the conformation of the loop AB for high- and low-affinity binding.
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Affiliation(s)
- Oktay K Gasymov
- Department of Pathology, University of California at Los Angeles, USA.
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12
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Gasymov OK, Abduragimov AR, Glasgow BJ. pH-Dependent conformational changes in tear lipocalin by site-directed tryptophan fluorescence. Biochemistry 2010; 49:582-90. [PMID: 20025287 DOI: 10.1021/bi901435q] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Tear lipocalin (TL), a major protein of human tears, binds a broad array of endogenous ligands. pH-dependent ligand binding in TL may have functional implications in tears. Previously, conformational selections of the AB and GH loops have been implicated in ligand binding by site-directed tryptophan fluorescence (SDTF). In this study, SDTF was applied to the AB and GH loops to investigate pH-driven conformational changes relevant to ligand binding. Both loops demonstrate significant but distinct conformational rearrangements over a wide pH range. In the low-pH transition, from 7.3 to 3.0, residues of the GH loop exhibit decreased solvent accessibilities. In acrylamide quenching experiments, the average quenching rate constant (k(q), accessibility parameter) of the residues in the GH loop is decreased approximately 38%, from 2.1 x 10(9) to 1.3 x 10(9) M(-1) s(-1). However, despite the significant changes in accessibilities for some residues in the AB loop, the average accessibility per residue remained unchanged (average k(q) = 1.2 M(-1) s(-1)). Accordingly, the low-pH transition induces conformational changes that reshuffle the accessibility profiles of the residues in the AB loop. A significant difference in the titration curves between the holo and apo forms of the W28 mutant suggests that the protonation states of the residues around position 28 modulate conformational switches of the AB loop relevant to ligand binding.
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Affiliation(s)
- Oktay K Gasymov
- Department of Pathology, UCLA School of Medicine, Jules Stein Eye Institute, 100 Stein Plaza, Los Angeles, California 90095, USA
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Gasymov OK, Abduragimov AR, Glasgow BJ. Intracavitary ligand distribution in tear lipocalin by site-directed tryptophan fluorescence. Biochemistry 2009; 48:7219-28. [PMID: 19586017 DOI: 10.1021/bi9005557] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Site-directed tryptophan fluorescence has been successfully used to determine the solution structure of tear lipocalin. Here, the technique is extended to measure the binding energy landscape. Single Trp mutants of tear lipocalin are bound to the native ligand and an analogue tagged with a quencher group to both populate and discriminate the excited protein states. Steady-state and time-resolved fluorescence quenching data reveal the intracavitary state of the ligand. The static components of fluorescence quenching identify the residues where nonfluorescence complexes form. An asymmetric distribution of the ligand within the cavity reflects the complex energy landscape of the excited protein states. These findings suggest that the excited protein states are not unique but consist of many substates. The roughness of the binding energy landscape is about 2.5kBT. The excited protein states originate primarily from conformational selections of loops AB and GH, a portal region. In contrast to static quenching, the dynamic components of fluorescence quenching by the ligand are relevant to both local side chain and ligand dynamics. Apparent bimolecular rate constants for collisional quenching of Trp by the nitroxide moiety are approximately 1 / 5 x 10(12) M(-1) s(-1). Estimations made for effective ligand concentrations establish actual rate constants on the order of 12 x 10(9) M(-1) s(-1). Prior to exit from the cavity of the protein, ligands explore binding sites in nanoseconds. Although microsecond fluctuations are rate-limiting processes in ligand binding for many proteins, accompanying nanosecond motion may be necessary for propagation of ligand binding.
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Affiliation(s)
- Oktay K Gasymov
- Department of Pathology, UCLA School of Medicine, Jules Stein Eye Institute, 100 Stein Plaza, Los Angeles, California 90095, USA
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Gasymov OK, Abduragimov AR, Glasgow BJ. Characterization of fluorescence of ANS-tear lipocalin complex: evidence for multiple-binding modes. Photochem Photobiol 2008; 83:1405-14. [PMID: 18028215 DOI: 10.1111/j.1751-1097.2007.00180.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
ANS is widely used as a probe for locating binding sites of proteins and studying structural changes under various external conditions. However, the nature of ANS-binding sites in proteins and the accompanying changes in fluorescence properties are controversial. We examined the steady-state and time-resolved fluorescence of the ANS-protein complexes for tear lipocalin (TL) and its mutants in order to discern the origin of lifetime components via analysis that included the multiexponential decay and the model-free maximum entropy methods. Fluorescence lifetimes of ANS-TL complexes can be grouped into two species, 14.01-17.42 ns and 2.72-4.37 ns. The log-normal analyses of fluorescence spectral shapes reveal the heterogeneous nature of both long- and short-lifetime species. The constructed time-resolved emission, amplitude (TRES) and area normalized (TRANES), and decay-associated spectra are consistent with a model that includes heterogeneous modes of ANS binding with two separate lifetime components. The two lifetime components are not derived from solvent relaxation, but rather may represent different binding modes.
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Affiliation(s)
- Oktay K Gasymov
- Department of Pathology, UCLA School of Medicine, Jules Stein Eye Institute, Los Angeles, CA, USA
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Gasymov OK, Abduragimov AR, Glasgow BJ. Ligand binding site of tear lipocalin: contribution of a trigonal cluster of charged residues probed by 8-anilino-1-naphthalenesulfonic acid. Biochemistry 2008; 47:1414-24. [PMID: 18179255 DOI: 10.1021/bi701955e] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Human tear lipocalin (TL) exhibits diverse functions, most of which are linked to ligand binding. To map the binding site of TL for some amphiphilic ligands, we capitalized on the hydrophobic and hydrophilic properties of 8-anilino-1-naphthalenesulfonic acid (ANS). In single Trp mutants, resonance energy transfer from Trp to ANS indicates that the naphthalene group of ANS is proximate to Leu105 in the cavity. Binding energies of TL to ANS and its analogues reveal contributions from electrostatic interactions. The sulfonate group of ANS interacts strongly with the nonconserved intracavitary residue Lys114 and less with neighboring residues His84 and Glu34. This trigonal cluster of residues may play a role in the ligand recognition site for some negatively charged ligands. Because many drugs possess sulfonate groups, the trigonal cluster-sulfonate interaction can also be exploited as a lipocalin-based drug delivery mechanism. The binding of lauric acid and its analogues shows that fatty acids assume heterogeneous orientations in the cavity of TL. Predominantly, the hydrocarbon tail is buried in the cavity of TL and the carboxyl group is oriented toward the mouth. However, TL can also interact, albeit relatively weakly, with fatty acids oriented in the opposite direction. As the major lipid binding protein of tears, the ability to accommodate fatty acids in two opposing orientations may have functional implications for TL. At the aqueous-lipid interface, fatty acids whose carboxyl groups are positioned toward the aqueous phase are available for interaction with TL that could augment stability of the tear film.
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Affiliation(s)
- Oktay K Gasymov
- Department of Pathology, Jules Stein Eye Institute, UCLA School of Medicine, 100 Stein Plaza, Los Angeles, California 90095, USA
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16
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Gasymov OK, Abduragimov AR, Glasgow BJ. Site-directed circular dichroism of proteins: 1Lb bands of Trp resolve position-specific features in tear lipocalin. Anal Biochem 2007; 374:386-95. [PMID: 18047823 DOI: 10.1016/j.ab.2007.11.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2007] [Revised: 10/31/2007] [Accepted: 11/01/2007] [Indexed: 10/22/2022]
Abstract
The absorption spectra of N-acetyl-L-tryptophanamide in various solvents were resolved into the sums of the (1)L(a) and (1)L(b) components. The relative intensities of the 0-0 transitions of the (1)L(b) bands correlate linearly with the solvent polarity values (E(T)(N)). A novel strategy that uses a set of the experimental (1)L(b) bands was employed to resolve the near-UV circular dichroism (CD) spectra of tryptophanyl residues. Resolved spectral parameters from the single-tryptophan mutants of tear lipocalin (TL), F99W and Y87W, corroborate the fluorescence and structural data of TL. Analysis of the (1)L(b) bands of the Trp CD spectra in proteins is a valuable tool to obtain the local features. The dimethyl sulfoxide (DMSO)-like (1)L(b) band of Trp CD spectra may be used as a "fingerprint" to identify the tryptophanyl side chains in situations where the benzene rings of Trp have van der Waals interactions with the side chains of its nearest neighbor. In addition, the signs and intensities of the components hold information about the side chain conformations and dynamics in proteins. Combined with Trp mutagenesis, this method, which we call site-directed circular dichroism, is broadly applicable to various proteins to obtain the position-specific data.
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Affiliation(s)
- Oktay K Gasymov
- Departments of Pathology and Ophthalmology, UCLA School of Medicine, Los Angeles, CA 90095, USA
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17
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Evidence for internal and external binding sites on human tear lipocalin. Arch Biochem Biophys 2007; 468:15-21. [PMID: 17945179 DOI: 10.1016/j.abb.2007.09.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2007] [Revised: 09/13/2007] [Accepted: 09/16/2007] [Indexed: 11/23/2022]
Abstract
8-anilino-1-naphthalenesulfonic acid (ANS) is widely used as a probe for locating binding sites of proteins. To characterize the binding sites of tear lipocalin (TL), we studied ANS binding to apoTL by steady-state and time-resolved fluorescence. Deconvolution of ANS binding revealed that two lifetime components, 16.99ns and 2.76ns at pH 7.3, have dissociation constants of 0.58muM and 5.7muM, respectively. At pH 3.0, the lifetime components show decreased affinities with dissociation constants of 2.42muM and approximately 21muM, respectively. Selective displacement of ANS molecules from the ANS-apoTL complex by stearic acid discriminates the internal and external binding sites. Dependence of the binding affinity on ionic strength under various conditions provides strong evidence that an electrostatic interaction is involved. Time-resolved fluorescence is a promising tool to segregate multiple binding sites of proteins.
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18
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Gasymov OK, Abduragimov AR, Merschak P, Redl B, Glasgow BJ. Oligomeric state of lipocalin-1 (LCN1) by multiangle laser light scattering and fluorescence anisotropy decay. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2007; 1774:1307-15. [PMID: 17869594 PMCID: PMC2040513 DOI: 10.1016/j.bbapap.2007.07.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2007] [Revised: 07/22/2007] [Accepted: 07/31/2007] [Indexed: 11/26/2022]
Abstract
Multiangle laser light scattering and fluorescence anisotropy decay measurements clarified the oligomeric states of native and recombinant tear lipocalin (lipocalin-1, TL). Native TL is monomeric. Recombinant TL (5-68 microM) with or without the histidine tag shows less than 7% dimer formation that is not in equilibrium with the monomeric form. Fluorescence anisotropy decay showed a correlation time of 9-10 ns for TL (10 microM-1 mM). Hydrodynamic calculations based on the crystallographic structure of a monomeric TL mutant closely concur with the observed correlation time. The solution properties calculated with HYDROPRO and SOLPRO programs from the available crystallographic structure of a monomeric TL mutant concur closely with the observed fluorescence anisotropy decay. The resulting model shows that protein topology is the major determinant of rotational correlation time and accounts for deviation from the Stokes-Einstein relation. The data challenge previous gel filtration studies to show that native TL exists predominantly as a monomer in solution rather than as a dimer. Delipidation of TL results in a formation of a complex oligomeric state (up to 25%). These findings are important as the dynamic processes in the tear film are limited by diffusional, translational as well as rotational, properties of the protein.
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Affiliation(s)
- Oktay K Gasymov
- Department of Pathology, UCLA School of Medicine, Los Angeles, CA 90095, USA
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19
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Gasymov OK, Abduragimov AR, Glasgow BJ. Molten globule state of tear lipocalin: ANS binding restores tertiary interactions. Biochem Biophys Res Commun 2007; 357:499-504. [PMID: 17434452 PMCID: PMC1952184 DOI: 10.1016/j.bbrc.2007.03.186] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2007] [Accepted: 03/28/2007] [Indexed: 11/25/2022]
Abstract
Tear lipocalin (TL) may stabilize the lipid layer of tears through a molten globule state triggered by low pH. EPR spectroscopy with site-directed spin labeling, revealed the side chain mobility of residues on the G-strand of TL in a molten globule state; the G-strand retains beta-sheet structure. All of the side chains of G-strand residues become more loosely packed, especially residues 96-99. In contrast, the highly mobile side chain of residue 95 on the F-G loop, becomes tightly packed. ANS binding to TL in a molten globule state reestablishes tight packing around side chains that are oriented both inside and outside of the barrel. Unlike RBP and BLG; TL has no disulfide bond between G- and H-strands. It is likely that the central beta-sheet in the molten globule state of lipocalins is stabilized by its interactions with the main alpha-helix, rather than the interstrand disulfide bond.
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Affiliation(s)
| | | | - Ben J. Glasgow
- *Corresponding author: Ben J. Glasgow, Departments of Pathology and Ophthalmology, UCLA School of Medicine, Jules Stein Eye Institute, 100 Stein Plaza, Rm# B269, Los Angeles, CA 90095, USA, (310) 825–6998,
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20
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Mori M, Takeuchi H, Sato M, Sumitomo S. Antimicrobial Peptides in Saliva and Salivary Glands: Their Roles in the Oral Defense System. ACTA ACUST UNITED AC 2006. [DOI: 10.3353/omp.11.1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Masahiko Mori
- Department of Oral and Maxillofacial Surgery, Asahi University School of Dentistry
| | - Hiroshi Takeuchi
- Department of Oral Pathology, Asahi University School of Dentistry
| | - Masaru Sato
- Department of Oral Pathology, Asahi University School of Dentistry
| | - Shinichiro Sumitomo
- Department of Oral and Maxillofacial Surgery, Asahi University School of Dentistry
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21
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Gasymov OK, Abduragimov AR, Yusifov TN, Glasgow BJ. Resolving near-ultraviolet circular dichroism spectra of single trp mutants in tear lipocalin. Anal Biochem 2003; 318:300-8. [PMID: 12814635 DOI: 10.1016/s0003-2697(03)00215-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Near-ultraviolet circular dichroism (near-UV CD) spectra of tryptophan residues in proteins are complicated because the line shapes are derived from the overlap of both the 1L(a) and the 1L(b) electronic bands that vary independently. Contributing to this complexity, tryptophan near-UV CD spectra differ in the relative amplitude of the 0-0 vibronic band compared to the rest of the 1L(b) spectrum, an inherent feature that may result in poor fitting. To resolve this problem, a computer program that incorporated the separation of the 0-0 transition of 1L(b) component from the rest of the 1L(b) was written in LabVIEW and its amplitude was allowed to vary independently. This method showed dramatically improved fitting of 1L(a) and 1L(b) components in the near-UV CD tryptophan spectra in tear lipocalin mutants featuring low intensity of the 0-0 1L(b) component. Side chain dynamic characteristics (mobility and accessibility to the solvent) identified from different spectroscopic techniques were related to differences in Trp near-UV CD spectra. This method is broadly applicable to different types of Trp near-UV CD spectra.
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Affiliation(s)
- Oktay K Gasymov
- Department of Pathology and Department of Ophthalmology, UCLA School of Medicine, Los Angeles, CA 90095, USA
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22
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Lögdberg L, Wester L. Immunocalins: a lipocalin subfamily that modulates immune and inflammatory responses. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1482:284-97. [PMID: 11058769 DOI: 10.1016/s0167-4838(00)00164-3] [Citation(s) in RCA: 143] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A subset of the lipocalins, notably alpha(1)-acid glycoprotein, alpha(1)-microglobulin, and glycodelin, exert significant immunomodulatory effects in vitro. Interestingly, all three are encoded from the q32-34 region of human chromosome 9, together with at least four other lipocalins (neutrophil gelatinase-associated lipocalin, complement factor gamma-subunit, tear prealbumin, and prostaglandin D synthase) that also may have anti-inflammatory and/or antimicrobial activity. This review addresses important features of this genetically linked subfamily of lipocalins (involvement with the acute phase response, immunomodulatory and anti-inflammatory properties, the tissue localization, complex formation with other proteins and receptors, etc.). It is likely that these proteins have evolved to be an integrated part of the body's defense system as part of the extended cytokine network. Its members exert a regulatory, dampening influence on the inflammatory cascade, thereby protecting against tissue damage from excessive inflammation. That most major mammalian allergens are lipocalins may reflect this connection of lipocalins with the immune system. We propose that this immunologically active lipocalin subset be named the 'immunocalins', signifying not only the structural homology and close genetic linkage of its members, but also their protective involvement with immunological and inflammatory processes. As immune mediators, immunocalins appear to use at least three interactive sites: the lipocalin 'pocket', binding sites for other plasma proteins, and binding sites for cell surface receptors.
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Affiliation(s)
- L Lögdberg
- Laboratory of Stem Cell Biology, New York Blood Center, NY 10021, USA.
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23
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Gasymov OK, Abduragimov AR, Yusifov TN, Glasgow BJ. Resolution of ligand positions by site-directed tryptophan fluorescence in tear lipocalin. Protein Sci 2000; 9:325-31. [PMID: 10716184 PMCID: PMC2144538 DOI: 10.1110/ps.9.2.325] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
The lipocalin superfamily of proteins functions in the binding and transport of a variety of important hydrophobic molecules. Tear lipocalin is a promiscuous lipid binding member of the family and serves as a paradigm to study the molecular determinants of ligand binding. Conserved regions in the lipocalins, such as the G strand and the F-G loop, may play an important role in ligand binding and delivery. We studied structural changes in the G strand of holo- and apo-tear lipocalin using spectroscopic methods including circular dichroism analysis and site-directed tryptophan fluorescence. Apo-tear lipocalin shows the same general structural characteristics as holo-tear lipocalin including alternating periodicity of a beta-strand, orientation of amino acid residues 105, 103, 101, and 99 facing the cavity, and progressive depth in the cavity from residues 105 to 99. For amino acid residues facing the internal aspect of cavity, the presence of a ligand is associated with blue shifted spectra. The collisional rate constants indicate that these residues are not less exposed to solvent in holo-tear lipocalin than in apo-tear lipocalin. Rather the spectral blue shifts may be accounted for by a ligand induced rigidity in holo-TL. Amino acid residues 94 and 95 are consistent with positions in the F-G loop and show greater exposure to solvent in the holo- than the apo-proteins. These findings are consistent with the general hypothesis that the F-G loop in the holo-proteins of the lipocalin family is available for receptor interactions and delivery of ligands to specific targets. Site-directed tryptophan fluorescence was used in combination with a nitroxide spin labeled fatty acid analog to elucidate dynamic ligand interactions with specific amino acid residues. Collisional quenching constants of the nitroxide spin label provide evidence that at least three amino acids of the G strand residues interact with the ligand. Stern-Volmer plots are inconsistent with a ligand that is held in a static position in the calyx, but rather suggest that the ligand is in motion. The combination of site-directed tryptophan fluorescence with quenching by nitroxide labeled species has broad applicability in probing specific interactions in the solution structure of proteins and provides dynamic information that is not attainable by X-ray crystallography.
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Affiliation(s)
- O K Gasymov
- Department of Pathology, UCLA School of Medicine, Los Angeles, California 90095, USA
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24
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Gasymov OK, Abduragimov AR, Yusifov TN, Glasgow BJ. Interaction of tear lipocalin with lysozyme and lactoferrin. Biochem Biophys Res Commun 1999; 265:322-5. [PMID: 10558865 DOI: 10.1006/bbrc.1999.1668] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The interaction of human tear lipocalin with lysozyme and lactoferrin was studied by electron paramagnetic resonance (EPR) spectroscopy. TL mutants I98C and F99C were spin labeled with MTSL and its derivative. The spectra demonstrated that at sites C98 and C99 the mobility of the nitroxides was reduced in the presence of lysozyme, lactoferrin, but not albumin. The reduced mobility was manifested as a reduction in side chain motion and backbone fluctuations. The overall correlation time of tear lipocalin, measured by MTSL derivative-labeled F99C, was prolonged in the presence of lysozyme and lactoferrin indicating that the interaction involves direct contact. The effect was mitigated at high salt concentration suggesting an electrostatic interaction of the molecules. The reduction in side chain mobility at C98 and C99 of tear lipocalin was observed in tears. Taken together, the data indicate that tear lipocalin interacts with both lysozyme and lactoferrin and suggest that they may function in concert with one another.
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Affiliation(s)
- O K Gasymov
- Department of Ophthalmology, UCLA School of Medicine, Los Angeles, California, 90095, USA
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25
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Gasymov OK, Abduragimov AR, Yusifov TN, Glasgow BJ. Binding studies of tear lipocalin: the role of the conserved tryptophan in maintaining structure, stability and ligand affinity. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1433:307-20. [PMID: 10515687 DOI: 10.1016/s0167-4838(99)00133-8] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
The principal lipid binding protein in tears, tear lipocalin (TL), binds acid and the fluorescent fatty acid analogs, DAUDA and 16-AP at one site TL compete for this binding site. A fluorescent competitive binding assay revealed that apo-TL has a high affinity for phospholipids and stearic acid (Ki) of 1.2 microM and 1.3 microM, respectively, and much less affinity for cholesterol (Ki) of 15.9 of the hydrocarbon chain. TL binds most strongly the least soluble lipids permitting these lipids to exceed their maximum solubility in aqueous solution. These data implicate TL in solubilizing and transporting lipids in the tear film. Phenylalanine, tyrosine and cysteine+ were substituted for TRP 17, the only invariant residue throughout the lipocalin superfamily. Cysteine substitution resulted in some loss os secondary structure, relaxation of aromatic side chain rigidity, decreased binding affinity for DAUDA and destabilization of structure. Mutants of TL, W17Y, and W17F showed a higher binding affinity for DAUDA than wild-type TL. Comparison of the results of the tryptophan 17 substitution in lipocalin with those of tryptophan 19 substitution in beta-lactoglobulin revealed important differences in binding characteristics that reflect the functional heterogeneity within the lipocalin family.
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Affiliation(s)
- O K Gasymov
- Department of Pathology, UCLA School of Medicine, Jules Stein Eye Institute, 100 Stein Plaza, Los Angeles, CA 90095, USA
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26
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Glasgow BJ, Abduragimov AR, Yusifov TN, Gasymov OK. Studies of ligand binding and CD analysis with apo- and holo-tear lipocalins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1998; 438:105-12. [PMID: 9634872 DOI: 10.1007/978-1-4615-5359-5_14] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- B J Glasgow
- Department of Pathology, University of California, Los Angeles School of Medicine, USA
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27
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Ressot C, Lassagne H, Kemeny JL, Gachon AM. Tissue expression of tear lipocalin in humans. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1998; 438:69-73. [PMID: 9634865 DOI: 10.1007/978-1-4615-5359-5_7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- C Ressot
- Laboratoire de Biochimie Médicale, Faculté de Médecine, Clermont-Ferrand Cedex, France
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28
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Mathers WD, Lane JA. Meibomian gland lipids, evaporation, and tear film stability. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1998; 438:349-60. [PMID: 9634908 DOI: 10.1007/978-1-4615-5359-5_50] [Citation(s) in RCA: 143] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- W D Mathers
- University of Iowa Hospitals and Clinics, Department of Ophthalmology, Iowa City, USA
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29
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Lacazette E, Pitiot G, Mallet J, Gachon AM. Dinucleotide repeat polymorphism near the tear lipocalin gene. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1998; 438:101-3. [PMID: 9634871 DOI: 10.1007/978-1-4615-5359-5_13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- E Lacazette
- Laboratoire de Biochimie Médicale, Faculté de Médecine, Clermont-Ferrand, France
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30
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Dewald G, Cichon S, Bryant SP, Hemmer S, Nöthen MM, Spurr NK. The human complement C8G gene, a member of the lipocalin gene family: polymorphisms and mapping to chromosome 9q34.3. Ann Hum Genet 1996; 60:281-91. [PMID: 8865989 DOI: 10.1111/j.1469-1809.1996.tb01192.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Complement component C8 is a plasma glycoprotein consisting of three nonidentical polypeptide chains (alpha, beta, gamma) which are encoded by three separate genes (C8A, C8B, C8G). The gamma chain whose functional role remains undefined is not related to any other complement protein but is a member of the lipocalins, a family of proteins that bind small hydrophobic ligands. The present report describes the first known polymorphisms for the human C8G gene, namely one polymorphic site in exon 1 (207T/G) and two polymorphic sites in intron 1 (213 + 37G --> A; 213 + 65del3). Specific typing can be performed using simple polymerase chain reaction-based assays. C8G genotyping in eight CEPH reference families demonstrated that C8G is closely linked to a series of marker loci located in the most telomeric region of chromosome 9q. Multipoint analysis placed C8G with 1000:1 support distal to D9S207. C8G is thus located at 9q34.3. Remarkably, this chromosomal region contains at least four other lipocalin genes.
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Affiliation(s)
- G Dewald
- Institute of Human Genetics, University of Bonn, Germany
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31
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Glasgow BJ, Abduragimov AR, Farahbakhsh ZT, Faull KF, Hubbell WL. Tear lipocalins bind a broad array of lipid ligands. Curr Eye Res 1995; 14:363-72. [PMID: 7648862 DOI: 10.3109/02713689508999934] [Citation(s) in RCA: 138] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
To identify the native ligands of tear lipocalins, tear proteins were separated by size exclusion chromatography and the lipid content in the major protein fractions identified. Lipids extracted from native tears and purified tear lipocalins comigrated with fatty acids, fatty alcohols, phospholipids, glycolipids, and cholesterol on thin layer chromatograms. Abundant stearic and palmitic acids as well as cholesterol, and lesser amounts of lauric acid were specifically identified in extracts of purified lipocalins by gas chromatography-mass spectroscopy. A preliminary study of the ligand-protein interaction was carried out using nitroxide spin-labeled lipids.
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Affiliation(s)
- B J Glasgow
- Department of Ophthalmology, UCLA School of Medicine 90024, USA
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