1
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Jose J, Law RHP, Leung EWW, Wai DCC, Akhlaghi H, Chandrashekaran IR, Caradoc-Davies TT, Voskoboinik I, Feutrill J, Middlemiss D, Jeevarajah D, Bashtannyk-Puhalovich T, Giddens AC, Lee TW, Jamieson SMF, Trapani JA, Whisstock JC, Spicer JA, Norton RS. Fragment-based and structure-guided discovery of perforin inhibitors. Eur J Med Chem 2023; 261:115786. [PMID: 37716187 DOI: 10.1016/j.ejmech.2023.115786] [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] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Revised: 08/24/2023] [Accepted: 08/31/2023] [Indexed: 09/18/2023]
Abstract
Perforin is a pore-forming protein whose normal function enables cytotoxic T and natural killer (NK) cells to kill virus-infected and transformed cells. Conversely, unwanted perforin activity can also result in auto-immune attack, graft rejection and aberrant responses to pathogens. Perforin is critical for the function of the granule exocytosis cell death pathway and is therefore a target for drug development. In this study, by screening a fragment library using NMR and surface plasmon resonance, we identified 4,4-diaminodiphenyl sulfone (dapsone) as a perforin ligand. We also found that dapsone has modest (mM) inhibitory activity of perforin lytic activity in a red blood cell lysis assay in vitro. Sequential modification of this lead fragment, guided by structural knowledge of the ligand binding site and binding pose, and supported by SPR and ligand-detected 19F NMR, enabled the design of nanomolar inhibitors of the cytolytic activity of intact NK cells against various tumour cell targets. Interestingly, the ligands we developed were largely inert with respect to direct perforin-mediated red blood cell lysis but were very potent in the context of perforin's action on delivering granzymes in the immune synapse, the context in which it functions physiologically. Our work indicates that a fragment-based, structure-guided drug discovery strategy can be used to identify novel ligands that bind perforin. Moreover, these molecules have superior physicochemical properties and solubility compared to previous generations of perforin ligands.
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Affiliation(s)
- Jiney Jose
- Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland, 1142, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, A New Zealand Centre for Research Excellence, Auckland, New Zealand
| | - Ruby H P Law
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC, 3800, Australia
| | - Eleanor W W Leung
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia
| | - Dorothy C C Wai
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia
| | - Hedieh Akhlaghi
- Cancer Immunology Program, Peter MacCallum Cancer Centre, 305 Grattan Street, Melbourne, VIC, 3000, Australia; Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, VIC, 3052, Australia
| | - Indu R Chandrashekaran
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia; ARC Centre for Fragment-Based Design, Monash University, Parkville, VIC, 3052, Australia
| | - Tom T Caradoc-Davies
- Australian Synchrotron, 800 Blackburn Rd., Clayton, Melbourne, VIC, 3168, Australia
| | - Ilia Voskoboinik
- Cancer Immunology Program, Peter MacCallum Cancer Centre, 305 Grattan Street, Melbourne, VIC, 3000, Australia; Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, VIC, 3052, Australia
| | - John Feutrill
- SYNthesis med chem (Australia) Pty Ltd, Bio21 Institute, 30 Flemington Road, Parkville, VIC, 3052, Australia
| | - David Middlemiss
- XaviaPharm, Bishop's Stortford, CM23 5EX, England, United Kingdom
| | - Devadharshini Jeevarajah
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC, 3800, Australia
| | | | - Anna C Giddens
- Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland, 1142, New Zealand
| | - Tet Woo Lee
- Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland, 1142, New Zealand
| | - Stephen M F Jamieson
- Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland, 1142, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, A New Zealand Centre for Research Excellence, Auckland, New Zealand; Department of Pharmacology and Clinical Pharmacology, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland, 1142, New Zealand
| | - Joseph A Trapani
- Cancer Immunology Program, Peter MacCallum Cancer Centre, 305 Grattan Street, Melbourne, VIC, 3000, Australia; Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, VIC, 3052, Australia
| | - James C Whisstock
- Department of Biochemistry and Molecular Biology, Monash University, Clayton, VIC, 3800, Australia.
| | - Julie A Spicer
- Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland, 1142, New Zealand; Maurice Wilkins Centre for Molecular Biodiscovery, A New Zealand Centre for Research Excellence, Auckland, New Zealand.
| | - Raymond S Norton
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC, 3052, Australia; ARC Centre for Fragment-Based Design, Monash University, Parkville, VIC, 3052, Australia.
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2
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Whitehouse RL, Alwan WS, Ilyichova OV, Taylor AJ, Chandrashekaran IR, Mohanty B, Doak BC, Scanlon MJ. Fragment screening libraries for the identification of protein hot spots and their minimal binding pharmacophores. RSC Med Chem 2023; 14:135-143. [PMID: 36760747 PMCID: PMC9890547 DOI: 10.1039/d2md00253a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2022] [Accepted: 11/11/2022] [Indexed: 11/30/2022] Open
Abstract
Fragment-based drug design relies heavily on structural information for the elaboration and optimisation of hits. The ability to identify neighbouring binding hot spots, energetically favourable interactions and conserved binding motifs in protein structures through X-ray crystallography can inform the evolution of fragments into lead-like compounds through structure-based design. The composition of fragment libraries can be designed and curated to fit this purpose and herein, we describe and compare screening libraries containing compounds comprising between 2 and 18 heavy atoms. We evaluate the properties of the compounds in these libraries and assess their ability to probe protein surfaces for binding hot spots.
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Affiliation(s)
- Rebecca L Whitehouse
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
| | - Wesam S Alwan
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
| | - Olga V Ilyichova
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
- Australian Synchrotron, ANSTO Clayton VIC 3168 Australia
- ARC Training Centre for Fragment Based Design, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
| | - Ashley J Taylor
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
| | - Indu R Chandrashekaran
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
- ARC Training Centre for Fragment Based Design, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
- Monash Fragment Platform, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
| | - Biswaranjan Mohanty
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
| | - Bradley C Doak
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
- ARC Training Centre for Fragment Based Design, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
- Monash Fragment Platform, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
| | - Martin J Scanlon
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
- ARC Training Centre for Fragment Based Design, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
- Monash Fragment Platform, Monash Institute of Pharmaceutical Sciences, Monash University Parkville VIC 3052 Australia
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3
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Pan Y, Chandrashekaran IR, Tennant L, Rossjohn J, Littler DR. Inside-out: Antibody-binding reveals potential folding hinge-points within the SARS-CoV-2 replication co-factor nsp9. PLoS One 2023; 18:e0283194. [PMID: 37036856 PMCID: PMC10085042 DOI: 10.1371/journal.pone.0283194] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Accepted: 03/03/2023] [Indexed: 04/11/2023] Open
Abstract
Nsp9 is a conserved accessory component of the coronaviral replication and transcription complex. It is the predominant substrate of nsp12's nucleotidylation activity while also serving to recruit proteins required for viral 5'-capping. Anti-nsp9 specific nanobodies have been isolated previously. We confirm that their binding mode is centred upon Trp-53 within SARS-CoV-2 nsp9. Antibody binding at this site surprisingly results in large-scale changes to the overall topology of this coronaviral unique fold. We further characterise the antibody-induced structural dynamism within nsp9, identifying a number of potentially flexible regions. A large expansion of the cavity between the s2-s3 and s4-s5 loops is particularly noteworthy. As is the potential for large-scale movements in the C-terminal GxxxG helix.
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Affiliation(s)
- Yue Pan
- Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | - Indu R Chandrashekaran
- Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | - Luke Tennant
- Infection and Immunity Program & Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
| | - Jamie Rossjohn
- Infection and Immunity Program & Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
- Institute of Infection and Immunity, Cardiff University School of Medicine, Heath Park, Cardiff, United Kingdom
| | - Dene R Littler
- Infection and Immunity Program & Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
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4
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Patil R, Mohanty B, Liu B, Chandrashekaran IR, Headey SJ, Williams ML, Clements CS, Ilyichova O, Doak BC, Genissel P, Weaver RJ, Vuillard L, Halls ML, Porter CJH, Scanlon MJ. A ligand-induced structural change in fatty acid-binding protein 1 is associated with potentiation of peroxisome proliferator-activated receptor α agonists. J Biol Chem 2018; 294:3720-3734. [PMID: 30598509 DOI: 10.1074/jbc.ra118.006848] [Citation(s) in RCA: 9] [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: 11/26/2018] [Revised: 12/17/2018] [Indexed: 01/15/2023] Open
Abstract
Peroxisome proliferator-activated receptor α (PPARα) is a transcriptional regulator of lipid metabolism. GW7647 is a potent PPARα agonist that must reach the nucleus to activate this receptor. In cells expressing human fatty acid-binding protein 1 (FABP1), GW7647 treatment increases FABP1's nuclear localization and potentiates GW7647-mediated PPARα activation; GW7647 is less effective in cells that do not express FABP1. To elucidate the underlying mechanism, here we substituted residues in FABP1 known to dictate lipid signaling by other intracellular lipid-binding proteins. Substitutions of Lys-20 and Lys-31 to Ala in the FABP1 helical cap affected neither its nuclear localization nor PPARα activation. In contrast, Ala substitution of Lys-57, Glu-77, and Lys-96, located in the loops adjacent to the ligand-binding portal region, abolished both FABP1 nuclear localization and GW7647-induced PPARα activation but had little effect on GW7647-FABP1 binding affinity. Using solution NMR spectroscopy, we determined the WT FABP1 structure and analyzed the dynamics in the apo and GW7647-bound structures of both the WT and the K57A/E77A/K96A triple mutant. We found that GW7647 binding causes little change in the FABP1 backbone, but solvent exposes several residues in the loops around the portal region, including Lys-57, Glu-77, and Lys-96. These residues also become more solvent-exposed upon binding of FABP1 with the endogenous PPARα agonist oleic acid. Together with previous observations, our findings suggest that GW7647 binding stabilizes a FABP1 conformation that promotes its interaction with PPARα. We conclude that full PPARα agonist activity of GW7647 requires FABP1-dependent transport and nuclear localization processes.
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Affiliation(s)
| | | | - Bonan Liu
- Drug Delivery, Disposition and Dynamics, and
| | | | | | | | | | | | | | - Patrick Genissel
- the Institut de Recherches Servier, 125 Chemin de Ronde, 78290 Croissy-sur-Seine, France
| | - Richard J Weaver
- the Institut de Recherches Servier, 125 Chemin de Ronde, 78290 Croissy-sur-Seine, France
| | - Laurent Vuillard
- the Institut de Recherches Servier, 125 Chemin de Ronde, 78290 Croissy-sur-Seine, France
| | - Michelle L Halls
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, 381 Royal Parade, Parkville, Victoria 3052, Australia and
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5
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Eldeeb K, Ganjiwale AD, Chandrashekaran IR, Padgett LW, Burgess J, Howlett AC, Cowsik SM. CB1 cannabinoid receptor-phosphorylated fourth intracellular loop structure-function relationships. Pept Sci (Hoboken) 2018; 111. [PMID: 32411924 DOI: 10.1002/pep2.24104] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
A peptide comprising the juxtamembrane C-terminal intracellular loop 4 (IL4) of the CB1 cannabinoid receptor possesses three Serine residues (Ser402, Ser411 and Ser415). Here we report the effect of Ser phosphorylation on the CB1 IL4 peptide conformation and cellular signaling functions using nuclear magnetic resonance spectroscopy, circular dichroism, G protein activation and cAMP production. Circular dichroism studies indicated that phosphorylation at various Ser residues induced helical structure in different environments. NMR data indicates that helical content varies in the order of IL4pSer411 > IL4pSer415 > IL4 > IL4pSer402. The efficacy of phosphorylated IL4 peptides in activating Go and Gi3 ([35S]GTPγS binding) and inhibiting cAMP accumulation in N18TG2 cells were correlated with helicity changes. Treatment of cells with bradykinin, which activates PKC, augmented CB1-mediated inhibition of cAMP accumulation, and this was reversed by a PKC inhibitor, suggesting that phosphorylation of serine might be a physiologically relevant modification in vivo. We conclude that phosphorylation-dependent alterations of helicity of CB1 IL4 peptides can increase efficacy of G protein signaling.
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Affiliation(s)
- Khalil Eldeeb
- Wake Forest University Health Sciences, Winston-Salem, NC, USA.,Al Azhar Faculty of Medicine, New Damietta, Egypt
| | - Anjali D Ganjiwale
- Department of Life Sciences, Bangalore University, Bangalore, Karnataka, India
| | | | - Lea W Padgett
- J.L. Chambers Biomedical Biotechnology Research Institute, North Carolina Central University, Durham, NC, USA
| | | | - Allyn C Howlett
- Wake Forest University Health Sciences, Winston-Salem, NC, USA.,J.L. Chambers Biomedical Biotechnology Research Institute, North Carolina Central University, Durham, NC, USA
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6
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Chandrashekaran IR, Norton RS, Schmitz-Peiffer C. Characterisation of peptide interactions that regulate PKCε activation. FEBS Lett 2018; 592:179-189. [PMID: 29266266 DOI: 10.1002/1873-3468.12953] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [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: 07/11/2017] [Revised: 11/13/2017] [Accepted: 12/10/2017] [Indexed: 11/09/2022]
Abstract
Targeting the interaction between PKC isoforms and their anchoring proteins can specifically regulate kinase activity. εV1-2 and pseudoεRACK peptides, derived from the PKCε C2 domain, modulate its association with receptor for activated C-kinase 2 (RACK2) and thus its function. Details of these interactions remain obscure, and we therefore investigated binding of these peptides using biophysical techniques. Surface plasmon resonance (SPR) indicated that the inhibitory εV1-2 peptide bound to RACK2, and inhibited PKCε binding as expected. In contrast, SPR and NMR demonstrated that the activating pseudoεRACK peptide and related sequences did not bind to PKCε, indicating that their mechanisms of action do not involve binding to the kinase as previously proposed. Our results clarify which interactions could be targeted in developing new therapeutics that inhibit PKCε-RACK2 interaction.
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Affiliation(s)
- Indu R Chandrashekaran
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Australia
| | - Raymond S Norton
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Australia
| | - Carsten Schmitz-Peiffer
- Diabetes and Metabolism Division, Garvan Institute of Medical Research, Darlinghurst, Australia.,St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, Australia
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7
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Norton RS, Leung EWW, Chandrashekaran IR, MacRaild CA. Applications of (19)F-NMR in Fragment-Based Drug Discovery. Molecules 2016; 21:molecules21070860. [PMID: 27438818 PMCID: PMC6273323 DOI: 10.3390/molecules21070860] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Revised: 06/21/2016] [Accepted: 06/21/2016] [Indexed: 11/16/2022] Open
Abstract
(19)F-NMR has proved to be a valuable tool in fragment-based drug discovery. Its applications include screening libraries of fluorinated fragments, assessing competition among elaborated fragments and identifying the binding poses of promising hits. By observing fluorine in both the ligand and the target protein, useful information can be obtained on not only the binding pose but also the dynamics of ligand-protein interactions. These applications of (19)F-NMR will be illustrated in this review with studies from our fragment-based drug discovery campaigns against protein targets in parasitic and infectious diseases.
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Affiliation(s)
- Raymond S Norton
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, Australia.
| | - Eleanor W W Leung
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, Australia.
| | - Indu R Chandrashekaran
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, Australia.
| | - Christopher A MacRaild
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville 3052, Australia.
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8
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Krishnarjuna B, Lim SS, Devine SM, Debono CO, Lam R, Chandrashekaran IR, Jaipuria G, Yagi H, Atreya HS, Scanlon MJ, MacRaild CA, Scammells PJ, Norton RS. Solution NMR characterization of apical membrane antigen 1 and small molecule interactions as a basis for designing new antimalarials. J Mol Recognit 2016; 29:281-91. [DOI: 10.1002/jmr.2529] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Accepted: 11/28/2015] [Indexed: 01/12/2023]
Affiliation(s)
- Bankala Krishnarjuna
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences; Monash University; 381 Royal Parade Parkville Victoria 3052 Australia
| | - San Sui Lim
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences; Monash University; 381 Royal Parade Parkville Victoria 3052 Australia
| | - Shane M. Devine
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences; Monash University; 381 Royal Parade Parkville Victoria 3052 Australia
| | - Cael O. Debono
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences; Monash University; 381 Royal Parade Parkville Victoria 3052 Australia
| | - Raymond Lam
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences; Monash University; 381 Royal Parade Parkville Victoria 3052 Australia
| | - Indu R. Chandrashekaran
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences; Monash University; 381 Royal Parade Parkville Victoria 3052 Australia
| | - Garima Jaipuria
- NMR Research Centre; Indian Institute of Science; Bangalore 560012 India
| | - Hiromasa Yagi
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences; Monash University; 381 Royal Parade Parkville Victoria 3052 Australia
| | | | - Martin J. Scanlon
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences; Monash University; 381 Royal Parade Parkville Victoria 3052 Australia
| | - Christopher A. MacRaild
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences; Monash University; 381 Royal Parade Parkville Victoria 3052 Australia
| | - Peter J. Scammells
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences; Monash University; 381 Royal Parade Parkville Victoria 3052 Australia
| | - Raymond S. Norton
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences; Monash University; 381 Royal Parade Parkville Victoria 3052 Australia
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9
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Chandrashekaran IR, Mohanty B, Linossi EM, Dagley LF, Leung EWW, Murphy JM, Babon JJ, Nicholson SE, Norton RS. Structure and Functional Characterization of the Conserved JAK Interaction Region in the Intrinsically Disordered N-Terminus of SOCS5. Biochemistry 2015; 54:4672-82. [PMID: 26173083 DOI: 10.1021/acs.biochem.5b00619] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
SOCS5 can negatively regulate both JAK/STAT and EGF-receptor pathways and has therefore been implicated in regulating both the immune response and tumorigenesis. Understanding the molecular basis for SOCS5 activity may reveal novel ways to target key components of these signaling pathways. The N-terminal region of SOCS5 coordinates critical protein interactions involved in inhibition of JAK/STAT signaling, and a conserved region within the N-terminus of SOCS5 mediates direct binding to the JAK kinase domain. Here we have characterized the solution conformation of this conserved JAK interaction region (JIR) within the largely disordered N-terminus of SOCS5. Using nuclear magnetic resonance (NMR) chemical shift analysis, relaxation measurements, and NOE analysis, we demonstrate the presence of preformed structural elements in the JIR of mouse SOCS5 (mSOCS5175-244), consisting of an α-helix encompassing residues 224-233, preceded by a turn and an extended structure. We have identified a phosphorylation site (Ser211) within the JIR of mSOCS5 and have investigated the role of phosphorylation in modulating JAK binding using site-directed mutagenesis.
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Affiliation(s)
- Indu R Chandrashekaran
- †Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, 381 Royal Parade, Parkville, Victoria 3052, Australia
| | - Biswaranjan Mohanty
- †Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, 381 Royal Parade, Parkville, Victoria 3052, Australia
| | - Edmond M Linossi
- §The Department of Medical Biology, University of Melbourne, Parkville, Victoria 3052, Australia
| | - Laura F Dagley
- §The Department of Medical Biology, University of Melbourne, Parkville, Victoria 3052, Australia
| | - Eleanor W W Leung
- †Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, 381 Royal Parade, Parkville, Victoria 3052, Australia
| | - James M Murphy
- §The Department of Medical Biology, University of Melbourne, Parkville, Victoria 3052, Australia
| | - Jeffrey J Babon
- §The Department of Medical Biology, University of Melbourne, Parkville, Victoria 3052, Australia
| | - Sandra E Nicholson
- §The Department of Medical Biology, University of Melbourne, Parkville, Victoria 3052, Australia
| | - Raymond S Norton
- †Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, 381 Royal Parade, Parkville, Victoria 3052, Australia
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10
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Devine SM, Mulcair MD, Debono CO, Leung EWW, Nissink JWM, Lim SS, Chandrashekaran IR, Vazirani M, Mohanty B, Simpson JS, Baell JB, Scammells PJ, Norton RS, Scanlon MJ. Promiscuous 2-aminothiazoles (PrATs): a frequent hitting scaffold. J Med Chem 2015; 58:1205-14. [PMID: 25559643 DOI: 10.1021/jm501402x] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
We have identified a class of molecules, known as 2-aminothiazoles (2-ATs), as frequent-hitting fragments in biophysical binding assays. This was exemplified by 4-phenylthiazol-2-amine being identified as a hit in 14/14 screens against a diverse range of protein targets, suggesting that this scaffold is a poor starting point for fragment-based drug discovery. This prompted us to analyze this scaffold in the context of an academic fragment library used for fragment-based drug discovery (FBDD) and two larger compound libraries used for high-throughput screening (HTS). This analysis revealed that such "promiscuous 2-aminothiazoles" (PrATs) behaved as frequent hitters under both FBDD and HTS settings, although the problem was more pronounced in the fragment-based studies. As 2-ATs are present in known drugs, they cannot necessarily be deemed undesirable, but the combination of their promiscuity and difficulties associated with optimizing them into a lead compound makes them, in our opinion, poor scaffolds for fragment libraries.
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Affiliation(s)
- Shane M Devine
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville, Victoria 3052, Australia
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11
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Lim SS, Yang W, Krishnarjuna B, Kannan Sivaraman K, Chandrashekaran IR, Kass I, MacRaild CA, Devine SM, Debono CO, Anders RF, Scanlon MJ, Scammells PJ, Norton RS, McGowan S. Structure and dynamics of apical membrane antigen 1 from Plasmodium falciparum FVO. Biochemistry 2014; 53:7310-20. [PMID: 25360546 DOI: 10.1021/bi5012089] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Apical membrane antigen 1 (AMA1) interacts with RON2 to form a protein complex that plays a key role in the invasion of host cells by malaria parasites. Blocking this protein-protein interaction represents a potential route to controlling malaria and related parasitic diseases, but the polymorphic nature of AMA1 has proven to be a major challenge to vaccine-induced antibodies and peptide inhibitors exerting strain-transcending inhibitory effects. Here we present the X-ray crystal structure of AMA1 domains I and II from Plasmodium falciparum strain FVO. We compare our new structure to those of AMA1 from P. falciparum 3D7 and Plasmodium vivax. A combination of normalized B factor analysis and computational methods has been used to investigate the flexibility of the domain I loops and how this correlates with their roles in determining the strain specificity of human antibody responses and inhibitory peptides. We also investigated the domain II loop, a key region involved in inhibitor binding, by comparison of multiple AMA1 crystal structures. Collectively, these results provide valuable insights that should contribute to the design of strain-transcending agents targeting P. falciparum AMA1.
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Affiliation(s)
- San Sui Lim
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University , Parkville, Victoria 3052, Australia
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12
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Devine SM, Lim SS, Chandrashekaran IR, MacRaild CA, Drew DR, Debono CO, Lam R, Anders RF, Beeson JG, Scanlon MJ, Scammells PJ, Norton RS. A critical evaluation of pyrrolo[2,3-d]pyrimidine-4-amines as Plasmodium falciparum apical membrane antigen 1 (AMA1) inhibitors. Med Chem Commun 2014. [DOI: 10.1039/c4md00090k] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Pyrrolo[2,3-d]pyrimidines are low affinity AMA1 binders that are also prone to aggregation.
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Affiliation(s)
- Shane M. Devine
- Medicinal Chemistry
- Monash Institute of Pharmaceutical Sciences
- Monash University
- Parkville, Australia
| | - San Sui Lim
- Medicinal Chemistry
- Monash Institute of Pharmaceutical Sciences
- Monash University
- Parkville, Australia
| | - Indu R. Chandrashekaran
- Medicinal Chemistry
- Monash Institute of Pharmaceutical Sciences
- Monash University
- Parkville, Australia
| | - Christopher A. MacRaild
- Medicinal Chemistry
- Monash Institute of Pharmaceutical Sciences
- Monash University
- Parkville, Australia
| | - Damien R. Drew
- Centre for Biomedical Research
- Burnet Institute
- Melbourne, Australia
| | - Cael O. Debono
- Medicinal Chemistry
- Monash Institute of Pharmaceutical Sciences
- Monash University
- Parkville, Australia
| | - Raymond Lam
- Medicinal Chemistry
- Monash Institute of Pharmaceutical Sciences
- Monash University
- Parkville, Australia
| | - Robin F. Anders
- Department of Biochemistry
- La Trobe University
- Melbourne, Australia
| | - James G. Beeson
- Centre for Biomedical Research
- Burnet Institute
- Melbourne, Australia
| | - Martin J. Scanlon
- Medicinal Chemistry
- Monash Institute of Pharmaceutical Sciences
- Monash University
- Parkville, Australia
- Centre of Excellence for Coherent X-Ray Science
| | - Peter J. Scammells
- Medicinal Chemistry
- Monash Institute of Pharmaceutical Sciences
- Monash University
- Parkville, Australia
| | - Raymond S. Norton
- Medicinal Chemistry
- Monash Institute of Pharmaceutical Sciences
- Monash University
- Parkville, Australia
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13
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Linossi EM, Chandrashekaran IR, Kolesnik TB, Murphy JM, Webb AI, Willson TA, Kedzierski L, Bullock AN, Babon JJ, Norton RS, Nicola NA, Nicholson SE. Suppressor of Cytokine Signaling (SOCS) 5 utilises distinct domains for regulation of JAK1 and interaction with the adaptor protein Shc-1. PLoS One 2013; 8:e70536. [PMID: 23990909 PMCID: PMC3749136 DOI: 10.1371/journal.pone.0070536] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Accepted: 06/20/2013] [Indexed: 12/02/2022] Open
Abstract
Suppressor of Cytokine Signaling (SOCS)5 is thought to act as a tumour suppressor through negative regulation of JAK/STAT and epidermal growth factor (EGF) signaling. However, the mechanism/s by which SOCS5 acts on these two distinct pathways is unclear. We show for the first time that SOCS5 can interact directly with JAK via a unique, conserved region in its N-terminus, which we have termed the JAK interaction region (JIR). Co-expression of SOCS5 was able to specifically reduce JAK1 and JAK2 (but not JAK3 or TYK2) autophosphorylation and this function required both the conserved JIR and additional sequences within the long SOCS5 N-terminal region. We further demonstrate that SOCS5 can directly inhibit JAK1 kinase activity, although its mechanism of action appears distinct from that of SOCS1 and SOCS3. In addition, we identify phosphoTyr317 in Shc-1 as a high-affinity substrate for the SOCS5-SH2 domain and suggest that SOCS5 may negatively regulate EGF and growth factor-driven Shc-1 signaling by binding to this site. These findings suggest that different domains in SOCS5 contribute to two distinct mechanisms for regulation of cytokine and growth factor signaling.
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Affiliation(s)
- Edmond M. Linossi
- Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- The University of Melbourne, Parkville, Victoria, Australia
| | - Indu R. Chandrashekaran
- Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | - Tatiana B. Kolesnik
- Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- The University of Melbourne, Parkville, Victoria, Australia
| | - James M. Murphy
- Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- The University of Melbourne, Parkville, Victoria, Australia
| | - Andrew I. Webb
- Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- The University of Melbourne, Parkville, Victoria, Australia
| | - Tracy A. Willson
- Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- The University of Melbourne, Parkville, Victoria, Australia
| | - Lukasz Kedzierski
- Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- The University of Melbourne, Parkville, Victoria, Australia
| | - Alex N. Bullock
- Structural Genomics Consortium, University of Oxford, Oxford, United Kingdom
| | - Jeffrey J. Babon
- Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- The University of Melbourne, Parkville, Victoria, Australia
| | - Raymond S. Norton
- Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | - Nicos A. Nicola
- Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- The University of Melbourne, Parkville, Victoria, Australia
| | - Sandra E. Nicholson
- Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- The University of Melbourne, Parkville, Victoria, Australia
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14
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Lim SS, Debono CO, MacRaild CA, Chandrashekaran IR, Dolezal O, Anders RF, Simpson JS, Scanlon MJ, Devine SM, Scammells PJ, Norton RS. Development of Inhibitors of Plasmodium falciparum Apical Membrane Antigen 1 Based on Fragment Screening. Aust J Chem 2013. [DOI: 10.1071/ch13266] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Apical membrane antigen 1 (AMA1) is an essential component of the moving junction complex used by Plasmodium falciparum to invade human red blood cells. AMA1 has a conserved hydrophobic cleft that is the site of key interactions with the rhoptry neck protein complex. Our goal is to develop small molecule inhibitors of AMA1 with broad strain specificity, which we are pursuing using a fragment-based approach. In our screening campaign, we identified fragments that bind to the hydrophobic cleft with a hit rate of 5 %. The high hit rate observed strongly suggests that a druggable pocket is present within the cleft.
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15
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Feng ZP, Chandrashekaran IR, Low A, Speed TP, Nicholson SE, Norton RS. The N-terminal domains of SOCS proteins: a conserved region in the disordered N-termini of SOCS4 and 5. Proteins 2012; 80:946-57. [PMID: 22423360 DOI: 10.1002/prot.23252] [Citation(s) in RCA: 30] [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: 12/30/2022]
Abstract
Suppressors of cytokine signaling (SOCS) proteins function as negative regulators of cytokine signaling and are involved in fine tuning the immune response. The structure and role of the SH2 domains and C-terminal SOCS box motifs of the SOCS proteins are well characterized, but the long N-terminal domains of SOCS4-7 remain poorly understood. Here, we present bioinformatic analyses of the N-terminal domains of the mammalian SOCS proteins, which indicate that these domains of SOCS4, 5, 6, and 7 are largely disordered. We have also identified a conserved region of about 70 residues in the N-terminal domains of SOCS4 and 5 that is predicted to be more ordered than the surrounding sequence. The conservation of this region can be traced as far back as lower vertebrates. As conserved regions with increased structural propensity that are located within long disordered regions often contain molecular recognition motifs, we expressed the N-terminal conserved region of mouse SOCS4 for further analysis. This region, mSOCS4₈₆₋₁₅₅, has been characterized by circular dichroism and nuclear magnetic resonance spectroscopy, both of which indicate that it is predominantly unstructured in aqueous solution, although it becomes helical in the presence of trifluoroethanol. The high degree of sequence conservation of this region across different species and between SOCS4 and SOCS5 nonetheless implies that it has an important functional role, and presumably this region adopts a more ordered conformation in complex with its partners. The recombinant protein will be a valuable tool in identifying these partners and defining the structures of these complexes.
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Affiliation(s)
- Zhi-Ping Feng
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia
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16
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Chandrashekaran IR, Adda CG, MacRaild CA, Anders RF, Norton RS. Inhibition by flavonoids of amyloid-like fibril formation by Plasmodium falciparum merozoite surface protein 2. Biochemistry 2010; 49:5899-908. [PMID: 20545323 DOI: 10.1021/bi902197x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Merozoite surface protein 2 (MSP2) is a glycosylphosphatidylinositol (GPI)-anchored protein expressed abundantly on the surface of Plasmodium falciparum merozoites. The results of a phase 2 trial in Papua New Guinean children showed MSP2 to be a promising malaria vaccine candidate. MSP2 is intrinsically unstructured and forms amyloid-like fibrils under physiological conditions. Oligomers containing beta-strand interactions similar to those in amyloid fibrils may be a component of the fibrillar surface coat on P. falciparum merozoites. As the propensity of MSP2 to form fibrils in solution also has the potential to impede its development as a vaccine candidate, finding an inhibitor that specifically inhibits fibrillogenesis may enhance vaccine development. In this study, we tested the ability of three flavonoids, EGCG, baicalein, and resveratrol, to inhibit MSP2 fibrillogenesis and found marked inhibition with EGCG but not with the other two flavonoids. The inhibitory effect and the interactions of the flavonoids with MSP2 were characterized using NMR spectroscopy, thioflavin T fluorescence assays, electron microscopy, and other biophysical methods. EGCG stabilizes soluble oligomers and blocks fibrillogenesis by preventing the conformational transition of MSP2 from a random coil to an amyloidogenic beta-sheet structure. Structural comparison of the three flavonoids indicates an association between their propensity for autoxidation and their fibril inhibitory activity; the activity of EGCG can be attributed to the vicinal hydroxyl groups present in this flavonoid and their ability to form quinones. The molecular mechanism of fibril inhibition by EGCG appears to be complex and involves noncovalent binding followed by covalent modification of the protein. Although the addition of EGCG appears to be an effective means of stabilizing MSP2 in solution, the covalent modification of MSP2 would most likely not be acceptable in a vaccine formulation. However, these small molecule inhibitors of MSP2 fibril formation will be useful as mechanistic probes in studying oligomerization and fibril assembly of MSP2.
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Affiliation(s)
- Indu R Chandrashekaran
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3052, Australia
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17
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Chandrashekaran IR, Rao GS, Cowsik SM. Molecular modeling of the peptide agonist-binding site in a neurokinin-2 receptor. J Chem Inf Model 2009; 49:1734-40. [PMID: 19534508 DOI: 10.1021/ci900055x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The neurokinin-2 receptor is a member of the rhodopsin family of G-protein coupled receptors, which represents one of the most relevant target families in small-molecule drug design. NK-2 receptors have been implicated in playing a pathophysiological role in asthma. Activation of the NK-2 receptor by its endogenous peptide agonist, tachykinins, is associated with diverse biological responses like bronchoconstriction, vasodepression, and regulation of endocrine functions. Agonist binding to the receptor is a crucial event in initiating signaling, and therefore characterization of the structural features of the agonists can reveal the molecular basis of receptor activation and help in rational design of novel therapeutics. In this study a molecular model for the interaction of the primary ligand NKA with its G-protein coupled receptor neurokinin-2 receptor has been developed. A three-dimensional model for the NK-2 receptor has been generated by homology modeling using rhodopsin as a template. A knowledge based docking of the NMR derived bioactive conformation of NKA to the receptor has been performed utilizing the ligand binding data obtained from the photoaffinity labeling and site-directed mutagenesis studies. The molecular model for the NKA/NK-2 receptor complex thus obtained sheds light on the topographical features of the binding pocket of the receptor and provides atomic insight into the biochemical data currently available for the receptor. The results of the receptor modeling studies have been used to discuss the molecular determinants for NK-2 receptor selectivity.
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18
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Low A, Chandrashekaran IR, Adda CG, Yao S, Sabo JK, Zhang X, Soetopo A, Anders RF, Norton RS. Merozoite surface protein 2 of Plasmodium falciparum: expression, structure, dynamics, and fibril formation of the conserved N-terminal domain. Biopolymers 2007; 87:12-22. [PMID: 17516503 DOI: 10.1002/bip.20764] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Merozoite surface protein 2 (MSP2) is a GPI-anchored protein on the surface of the merozoite stage of the malaria parasite Plasmodium falciparum. It is largely disordered in solution, but has a propensity to form amyloid-like fibrils under physiological conditions. The N-terminal conserved region (MSP2(1-25)) is part of the protease-resistant core of these fibrils. To investigate the structure and dynamics of this region, its ability to form fibrils, and the role of individual residues in these properties, we have developed a bacterial expression system that yields > or =10 mg of unlabeled or (15)N-labeled peptide per litre of culture. Two recombinant versions of MSP2(1-25), wild-type and a Y7A/Y16A mutant, have been produced. Detailed conformational analysis of the wild-type peptide and backbone (15)N relaxation data indicated that it contains beta-turn and nascent helical structures in the central and C-terminal regions. Residues 6-21 represent the most ordered region of the structure, although there is some flexibility around residues 8 and 9. The 10-residue sequence (MSP2(7-16)) (with two Tyr residues) was predicted to have a higher propensity for beta-aggregation than the 8-mer sequence (MSP2(8-15)), but there was no significant difference in conformation between MSP2(1-25) and [Y7A,Y16A]MSP2(1-25) and the rate of fibril formation was only slightly slower in the mutant. The peptide expression system described here will facilitate further mutational analyses to define the roles of individual residues in transient structural elements and fibril formation, and thus contribute to the further development of MSP2 as a malaria vaccine candidate.
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Affiliation(s)
- Andrew Low
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC 3050, Australia
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19
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Chandrashekaran IR, Yao S, Wang CC, Bansal PS, Alewood PF, Forbes BE, Wallace JC, Bach LA, Norton RS. The N-terminal subdomain of insulin-like growth factor (IGF) binding protein 6. Structure and interaction with IGFs. Biochemistry 2007; 46:3065-74. [PMID: 17305365 DOI: 10.1021/bi0619876] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [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: 11/30/2022]
Abstract
Insulin-like growth factor binding proteins (IGFBPs) modulate the activity and distribution of insulin-like growth factors (IGFs). IGFBP-6 differs from other IGFBPs in being a relatively specific inhibitor of IGF-II actions. Another distinctive feature of IGFBP-6 is its unique N-terminal disulfide linkages; the N-domains of IGFBPs 1-5 contain six disulfides and share a conserved GCGCC motif, but IGFBP-6 lacks the two adjacent cysteines in this motif, so its first three N-terminal disulfide linkages differ from those of the other IGFBPs. The contributions of the N- and C-domains of IGFBP-6 to its IGF binding properties and their structure-function relationships have been characterized in part, but the structure and function of the distinctive N-terminal subdomain of IGFBP-6 are unknown. Here we report the solution structure of a polypeptide corresponding to residues 1-45 of the N-terminal subdomain of IGFBP-6 (NN-BP-6). The extended structure of the N-terminal subdomain of IGFBP-6 is very different from that of the short two-stranded beta-sheet of the N-terminal subdomain of IGFBP-4 and, by implication, the other IGFBPs. NN-BP-6 contains a potential cation-binding motif; lanthanide ion binding was observed, but no significant interaction was found with physiologically relevant metal ions like calcium or magnesium. However, this subdomain of IGFBP-6 has a higher affinity for IGF-II than IGF-I, suggesting that it may contribute to the marked IGF-II binding preference of IGFBP-6. The extended structure and flexibility of this subdomain of IGFBP-6 could play a role in enhancing the rate of ligand association and thereby be significant in IGF recognition.
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Affiliation(s)
- Indu R Chandrashekaran
- The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville 3050, Australia
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