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Alba-Posse EJ, Bruque CD, Gándola Y, Gasulla J, Nadra AD. From in-silico screening to in-vitro evaluation: Enhancing the detection of Microcystins with engineered PP1 mutant variants. J Struct Biol 2023; 215:108043. [PMID: 37935286 DOI: 10.1016/j.jsb.2023.108043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2023] [Revised: 10/20/2023] [Accepted: 11/04/2023] [Indexed: 11/09/2023]
Abstract
Cyanotoxins produced during harmful algal blooms (CyanoHABs) have become a worldwide issue of concern. Microcystins (MC) are the most ubiquitous group of cyanotoxins and have known carcinogenic and hepatotoxic effects. The protein phosphatase inhibition assays (PPIAs), based on the inhibition of Protein Phosphatase 1/2A (PP1/PP2A) by MC, are one of the most cost-effective options for detecting MC. In this work, we aimed to design in-silico and evaluate in-vitro mutant variants of the PP1 protein, in order to enhance their capabilities as a MC biosensor. To this end, we performed an in-silico active site-saturated mutagenesis screening, followed by stability and docking affinity calculation with the MCLR cyanotoxin. Candidates with improved both affinity and stability were further tested in a fully flexible active-site docking. The best-scored mutations (19) were individually analysed regarding their locations and interactions. Four of them (p.D197F; p.Q249Y; p.S129W; p.D220Q) were selected for in-vitro expression and evaluation. Mutant p.D197F, exhibited a significant increment in inhibition by MCLR with respect to the WT, while showing a non-significant difference in stability nor activity. This successful PP1 inhibition enhancement suggests the potential of the p.D197F variant for practical MC detection applications.
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Affiliation(s)
- Ezequiel J Alba-Posse
- Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología y Biología Molecular y Celular, Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Universidad de Buenos Aires, Intendente Güiraldes 2160, C1428EGA Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Godoy Cruz 2290, C1425FQB Buenos Aires, Argentina
| | - Carlos David Bruque
- Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Godoy Cruz 2290, C1425FQB Buenos Aires, Argentina; Unidad de Conocimiento Traslacional Hospitalaria Patagónica, Hospital de Alta Complejidad El Calafate - S.A.M.I.C., Jorge Newbery 453, CP9405 El Calafate, Santa Cruz, Argentina
| | - Yamila Gándola
- Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología y Biología Molecular y Celular, Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Universidad de Buenos Aires, Intendente Güiraldes 2160, C1428EGA Buenos Aires, Argentina
| | - Javier Gasulla
- Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología y Biología Molecular y Celular, Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Universidad de Buenos Aires, Intendente Güiraldes 2160, C1428EGA Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Godoy Cruz 2290, C1425FQB Buenos Aires, Argentina.
| | - Alejandro D Nadra
- Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología y Biología Molecular y Celular, Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Universidad de Buenos Aires, Intendente Güiraldes 2160, C1428EGA Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Godoy Cruz 2290, C1425FQB Buenos Aires, Argentina.
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2
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Mukherjee M, Saha Sardar P, Basu Roy M, Mukherjee P, Ghosh R, Ghosh S. Tracking Zone-wise perturbation during unfolding of some globular proteins using Eu(III) complex of Tetracycline as a probe exhibiting Stark splitting. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2022; 264:120231. [PMID: 34365134 DOI: 10.1016/j.saa.2021.120231] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 07/14/2021] [Accepted: 07/24/2021] [Indexed: 06/13/2023]
Abstract
Enhanced 'Antenna effect' of a suitably designed ternary complex of Eu(III), Tetracycline hydrochloride (TC) and globular proteins viz bovine serum albumin (BSA), human serum albumin (HSA) and β-lactoglobulin A (BLGA) in aqueous medium is employed to characterize the different partially unfolded states along with investigation of the micro- heterogeneous environment of the proteins during their stepwise unfolding. The zone-wise perturbation for the proteins upon denaturation by Urea and Guanidine hydrochloride (Gdn. HCl) is followed by the emission of Eu(III) through 'Antenna Effect' and that of the tryptophan (Trp) residues of the proteins as a function of denaturants both by steady state and time resolved emission study. With Gdn. HCl as denaturant, both BSA and BLGA show quenching of Eu(III) emission compared to pure protein while HSA exhibits an enhancement of antenna effect during unfolding as compared to that in its absence. In the presence of Urea, HSA and BSA show enhancement of antenna effect accompanied by Stark splitting of the 5D0→7F2 transition of Eu(III) although BLGA follows the similar pattern of quenching of Eu(III) emission as observed with Gdn. HCl without any Stark splitting. The proteins exhibit a two state transition with ΔGD values of ~ 2-3 kcal mol-1. Thus the use of Eu(III) emission as an efficient probe is advocating here to rationalize the microenvironment of the proteins during their stepwise unfolding.
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Affiliation(s)
- Moumita Mukherjee
- Present Address: Sri Aurobindo Vidyamandir, Chandannagar, Hoogly, West Bengal, India
| | - Pinki Saha Sardar
- Department of Chemistry, The Bhawanipur Education Society College, Kolkata-700020, West Bengal, India
| | - Maitrayee Basu Roy
- Department of Chemistry, Vidyasagar College for Women, Kolkata-700006, West Bengal, India
| | - Priyanka Mukherjee
- Department of Chemistry and Biochemistry, Asutosh College, Kolkata-700026, India
| | - Rina Ghosh
- Department of Chemistry, St. Xavier's College, Kolkata-700013, India
| | - Sanjib Ghosh
- Department of Chemistry, Adamas University, Barasat, West Bengal, India.
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3
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Yadav J, Kumar Y, Singaraju GS, Patil S. Interaction of chloramphenicol with titin I27 probed using single-molecule force spectroscopy. J Biol Phys 2021; 47:191-204. [PMID: 34075502 DOI: 10.1007/s10867-021-09573-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2020] [Accepted: 05/05/2021] [Indexed: 11/28/2022] Open
Abstract
Titin is a giant elastic protein which is responsible for passive muscle stiffness when muscle sarcomeres are stretched. Chloramphenicol, besides being a broad-spectrum antibiotic, also acts as a muscle relaxant. Therefore, it is important to study the interaction between titin I27 and chloramphenicol. We investigated the interaction of chloramphenicol with octamer of titin I27 using single-molecule force spectroscopy and fluorescence spectroscopy. The fluorescence data indicated that binding of chloramphenicol with I27 results in fluorescence quenching. Furthermore, it is observed that chloramphenicol binds to I27 at a particular concentration ([Formula: see text] 40 μM). Single-molecule force spectroscopy shows that, in the presence of 40 μM chloramphenicol concentration, the I27 monomers become mechanically stable, resulting in an increment of the unfolding force. The stability was further confirmed by chemical denaturation experiments on monomers of I27, which corroborate the evidence for enhanced mechanical stability at 40 μM drug concentration. The free energy of stabilization for I27 (wild type) was found to be 1.95 ± 0.93 kcal/mole and I27 with 40 μM drug was 3.25 ± 0.63 kcal/mole. The results show a direct effect of the broad-spectrum antibiotic chloramphenicol on the passive elasticity of muscle protein titin. The I27 is stabilized both mechanically and chemically by chloramphenicol.
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Affiliation(s)
- Jyoti Yadav
- Indian Institute of Science Education and Research, Pune, India
| | - Yashwant Kumar
- Indian Institute of Science Education and Research, Pune, India
| | | | - Shivprasad Patil
- Indian Institute of Science Education and Research, Pune, India.
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4
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Pal S, Pyne P, Samanta N, Ebbinghaus S, Mitra RK. Thermal stability modulation of the native and chemically-unfolded state of bovine serum albumin by amino acids. Phys Chem Chem Phys 2020; 22:179-188. [DOI: 10.1039/c9cp04887a] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Cells are crowded with various cosolutes including salts, osmolytes, nucleic acids, peptides and proteins.
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Affiliation(s)
- Saikat Pal
- Department of Chemical
- Biological and Macromolecular Sciences
- S N Bose National Centre for Basic Sciences
- Kolkata 700106
- India
| | - Partha Pyne
- Department of Chemical
- Biological and Macromolecular Sciences
- S N Bose National Centre for Basic Sciences
- Kolkata 700106
- India
| | - Nirnay Samanta
- Institute for Physical and Theoretical Chemistry
- TU Braunschweig
- BRICS
- 56 D-38106 Braunschweig
- Germany
| | - Simon Ebbinghaus
- Institute for Physical and Theoretical Chemistry
- TU Braunschweig
- BRICS
- 56 D-38106 Braunschweig
- Germany
| | - Rajib Kumar Mitra
- Department of Chemical
- Biological and Macromolecular Sciences
- S N Bose National Centre for Basic Sciences
- Kolkata 700106
- India
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5
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Kovermann M, Stefan A, Castaldo A, Caramia S, Hochkoeppler A. Structural and catalytic insights into HoLaMa, a derivative of Klenow DNA polymerase lacking the proofreading domain. PLoS One 2019; 14:e0215411. [PMID: 30970012 PMCID: PMC6457538 DOI: 10.1371/journal.pone.0215411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Accepted: 04/01/2019] [Indexed: 11/18/2022] Open
Abstract
We report here on the stability and catalytic properties of the HoLaMa DNA polymerase, a Klenow sub-fragment lacking the 3’-5’ exonuclease domain. HoLaMa was overexpressed in Escherichia coli, and the enzyme was purified by means of standard chromatographic techniques. High-resolution NMR experiments revealed that HoLaMa is properly folded at pH 8.0 and 20°C. In addition, urea induced a cooperative folding to unfolding transition of HoLaMa, possessing an overall thermodynamic stability and a transition midpoint featuring ΔG and CM equal to (15.7 ± 1.9) kJ/mol and (3.5 ± 0.6) M, respectively. When the catalytic performances of HoLaMa were compared to those featured by the Klenow enzyme, we did observe a 10-fold lower catalytic efficiency by the HoLaMa enzyme. Surprisingly, HoLaMa and Klenow DNA polymerases possess markedly different sensitivities in competitive inhibition assays performed to test the effect of single dNTPs.
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Affiliation(s)
- Michael Kovermann
- Department of Chemistry, University of Konstanz, Universitätstraße, Konstanz, Germany
| | - Alessandra Stefan
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
- CSGI, University of Firenze, Sesto Fiorentino (Firenze), Italy
| | - Anna Castaldo
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Sara Caramia
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
| | - Alejandro Hochkoeppler
- Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy
- CSGI, University of Firenze, Sesto Fiorentino (Firenze), Italy
- * E-mail:
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6
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Yadav R, Sen P. Mechanistic investigation of domain specific unfolding of human serum albumin and the effect of sucrose. Protein Sci 2013; 22:1571-81. [PMID: 24038622 DOI: 10.1002/pro.2357] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2013] [Revised: 07/27/2013] [Accepted: 08/16/2013] [Indexed: 11/07/2022]
Abstract
This study is devoted to understand the unfolding mechanism of a multidomain protein, human serum albumin (HSA), in absence and presence of the sucrose by steady-state and time-resolved fluorescence spectroscopy with domain specific marker molecules and is further being substantiated by molecular dynamics (MD) simulation. In water, the domain III of HSA found to unfold first followed by domains I and II as the concentration of GnHCl is increased in the medium. The sequential unfolding behavior of different domains of HSA remains same in presence of sucrose; however, a higher GnHCl concentration is required for unfolding, suggesting stabilizing effect of sucrose on HSA. Domain I is found to be most stabilized by sucrose. The stabilization of domain II is somewhat similar to domain I, but the effect of sucrose on domain III is found to be very small. MD simulation also predicted a similar behavior of sucrose on HSA. The stabilizing effect of sucrose is explained in terms of the entrapment of water molecules in between HSA surface and sucrose layer as well as direct interaction between HSA and sucrose.
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Affiliation(s)
- Rajeev Yadav
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208 016, Uttar Pradesh, India
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7
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Równicka-Zubik J, Sułkowski L, Maciążek-Jurczyk M, Sułkowska A. The effect of structural alterations of three mammalian serum albumins on their binding properties. J Mol Struct 2013. [DOI: 10.1016/j.molstruc.2012.12.049] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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8
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Maghsoudi S, Ashrafi-Kooshk MR, Shahlaei M, Ghadami SA, Ghobadi S, Mostafaie A, Khodarahmi R. Comparative evaluation of amphotericin B binding to the native and modified forms of rice lipid-transfer protein: a possible perspective on improving the drug-binding affinity and specificity. JOURNAL OF THE IRANIAN CHEMICAL SOCIETY 2013. [DOI: 10.1007/s13738-013-0231-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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9
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Amyloid fibril formation by native and modified bovine β-lactoglobulins proceeds through unfolded form of proteins: A comparative study. Biophys Chem 2011; 159:311-20. [DOI: 10.1016/j.bpc.2011.08.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Revised: 08/16/2011] [Accepted: 08/17/2011] [Indexed: 11/16/2022]
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10
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Biswas P, Bhattacherjee A. Role of foldability and stability in designing real protein sequences. Phys Chem Chem Phys 2011; 13:9223-31. [DOI: 10.1039/c0cp02973d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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11
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Togashi DM, Ryder AG, O’Shaughnessy D. Monitoring Local Unfolding of Bovine Serum Albumin During Denaturation Using Steady-State and Time-Resolved Fluorescence Spectroscopy. J Fluoresc 2009; 20:441-52. [DOI: 10.1007/s10895-009-0566-8] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2009] [Accepted: 11/03/2009] [Indexed: 11/28/2022]
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12
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Varshney A, Ahmad B, Khan RH. Comparative studies of unfolding and binding of ligands to human serum albumin in the presence of fatty acid: Spectroscopic approach. Int J Biol Macromol 2008; 42:483-90. [DOI: 10.1016/j.ijbiomac.2008.03.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2007] [Revised: 03/17/2008] [Accepted: 03/18/2008] [Indexed: 10/22/2022]
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13
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Haq SK, Rasheedi S, Sharma P, Ahmad B, Khan RH. Influence of salts and alcohols on the conformation of partially folded intermediate of stem bromelain at low pH. Int J Biochem Cell Biol 2005; 37:361-74. [PMID: 15474981 DOI: 10.1016/j.biocel.2004.07.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2004] [Revised: 06/23/2004] [Accepted: 07/09/2004] [Indexed: 11/26/2022]
Abstract
The effect of salts and alcohols was examined on the partially folded intermediate (PFI) state of stem bromelain reported at low pH (Haq, Rasheedi, and Khan (2002) European Journal of Biochemistry 269, 47-52) by a combination of optical methods like circular dichroism, intrinsic fluorescence and ANS binding. ESI mass spectrometry was also performed to see the effect, if any, on the overall tertiary structure of the protein. Increase in ionic strength by the addition of salts resulted in folded structures somewhat different from the native enzyme. Salt-induced intermediates are characterized by increase in helical content and a significantly reduced exposure of hydrophobic clusters relative to the state at pH 2.0. The emission wavelength maximum of intrinsic fluorescence was shifted towards that of native enzyme. ESI-MS data show decreased accessibility of ionizable/protonation sites suggestive of a folded structure. On the other hand, alcohol-induced intermediates though exhibiting increased helical content are apparently largely unfolded as observed by ESI. Thermal denaturation of a representative intermediate, each from the group of salts and alcohols examined, was also performed to check their relative stabilities. While the alcohol-induced state showed a cooperative thermal transition, the salt-induced state shows non-cooperative thermal denaturation.
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Affiliation(s)
- Soghra Khatun Haq
- Interdisciplinary Biotechnology Unit, Aligarh Muslim University, Aligarh 202002, India
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14
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Kamal JKA, Zhao L, Zewail AH. Ultrafast hydration dynamics in protein unfolding: human serum albumin. Proc Natl Acad Sci U S A 2004; 101:13411-6. [PMID: 15353599 PMCID: PMC518771 DOI: 10.1073/pnas.0405724101] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We report studies of unfolding and ultrafast hydration dynamics of the protein human serum albumin. Unique in this study is our ability to examine different domains of the same protein and the intermediate on the way to the unfolded state. With femtosecond resolution and site-selective labeling, we isolate the dynamics of domains I and II of the native protein, domain I of the intermediate at 2 M guanidine hydrochloride, and the unfolded state at 6 M of the denaturant. For studies of unfolding, we used the fluorophores, acrylodan (covalently bound to Cys-34 in domain I) and the intrinsic tryptophan (domain II), whereas for hydration dynamics, we probed acrylodan and prodan; the latter is bound to domain II. From the time-dependent spectra and the correlation functions, we obtained the time scale of dynamically ordered water: 57 ps for the more stable domain I and 32 ps for the less stable domain II, in contrast to approximately 0.8 ps for labile, bulk-type water. This trend suggests an increased hydrophilic residues-water interaction of domain I, contrary to some packing models. In the intermediate state, which is characterized by essentially intact domain I and unfolded domain II, the dynamics of ordered water around domain I is nearly the same (61 ps) as that of native state (57 ps), whereas that in the unfolded protein is much shorter (13 ps). We discuss the role of this fluidity in the correlation between stability and function of the protein.
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Affiliation(s)
- J K Amisha Kamal
- Laboratory for Molecular Sciences, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125, USA
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Santra MK, Banerjee A, Krishnakumar SS, Rahaman O, Panda D. Multiple-probe analysis of folding and unfolding pathways of human serum albumin. Evidence for a framework mechanism of folding. ACTA ACUST UNITED AC 2004; 271:1789-97. [PMID: 15096218 DOI: 10.1111/j.1432-1033.2004.04096.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The changes in the far-UV CD signal, intrinsic tryptophan fluorescence and bilirubin absorbance showed that the guanidine hydrochloride (GdnHCl)-induced unfolding of a multidomain protein, human serum albumin (HSA), followed a two-state process. However, using environment sensitive Nile red fluorescence, the unfolding and folding pathways of HSA were found to follow a three-state process and an intermediate was detected in the range 0.25-1.5 m GdnHCl. The intermediate state displayed 45% higher fluorescence intensity than that of the native state. The increase in the Nile red fluorescence was found to be due to an increase in the quantum yield of the HSA-bound Nile red. Low concentrations of GdnHCl neither altered the binding affinity of Nile red to HSA nor induced the aggregation of HSA. In addition, the secondary structure of HSA was not perturbed during the first unfolding transition (<1.5 m GdnHCl); however, the secondary structure was completely lost during the second transition. The data together showed that the half maximal loss of the tertiary structure occurred at a lower GdnHCl concentration than the loss of the secondary structure. Further kinetic studies of the refolding process of HSA using multiple spectroscopic techniques showed that the folding occurred in two phases, a burst phase followed by a slow phase. An intermediate with native-like secondary structure but only a partial tertiary structure was found to form in the burst phase of refolding. Then, the intermediate slowly folded into the native state. An analysis of the refolding data suggested that the folding of HSA could be best explained by the framework model.
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Affiliation(s)
- Manas Kumar Santra
- School of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Mumbai, India
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16
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Haq SK, Rasheedi S, Khan RH. Characterization of a partially folded intermediate of stem bromelain at low pH. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:47-52. [PMID: 11784297 DOI: 10.1046/j.0014-2956.2002.02620.x] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Equilibrium studies on the acid included denaturation of stem bromelain (EC 3.4.22.32) were performed by CD spectroscopy, fluorescence emission spectroscopy and binding of the hydrophobic dye, 1-anilino 8-naphthalene sulfonic acid (ANS). At pH 2.0, stem bromelain lacks a well defined tertiary structure as seen by fluorescence and near-UV CD spectra. Far-UV CD spectra show retention of some native like secondary structure at pH 2.0. The mean residue ellipticities at 208 nm plotted against pH showed a transition around pH 4.5 with loss of secondary structure leading to the formation of an acid-unfolded state. With further decrease in pH, this unfolded state regains most of its secondary structure. At pH 2.0, stem bromelain exists as a partially folded intermediate containing about 42.2% of the native state secondary structure Enhanced binding of ANS was observed in this state compared to the native folded state at neutral pH or completely unfolded state in the presence of 6 m GdnHCl indicating the exposure of hydrophobic regions on the protein molecule. Acrylamide quenching of the intrinsic tryptophan residues in the protein molecule showed that at pH 2.0 the protein is in an unfolded conformation with more tryptophan residues exposed to the solvent as compared to the native conformation at neutral pH. Interestingly, stem bromelain at pH 0.8 exhibits some characteristics of a molten globule, such as an enhanced ability to bind the fluorescent probe as well as considerable retention of secondary structure. All the above data taken together suggest the existence of a partially folded intermediate state under low pH conditions.
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Affiliation(s)
- Soghra Khatun Haq
- Interdisciplinary Biotechnology Unit, Aligarh Muslim University, India
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Flora K, Brennan JD, Baker GA, Doody MA, Bright FV. Unfolding of acrylodan-labeled human serum albumin probed by steady-state and time-resolved fluorescence methods. Biophys J 1998; 75:1084-96. [PMID: 9675210 PMCID: PMC1299783 DOI: 10.1016/s0006-3495(98)77598-8] [Citation(s) in RCA: 142] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Steady-state and time-resolved fluorescence spectroscopy was used to follow the local and global changes in structure and dynamics during chemical and thermal denaturation of unlabeled human serum albumin (HSA) and HSA with an acrylodan moiety bound to Cys34. Acrylodan fluorescence was monitored to obtain information about unfolding processes in domain I, and the emission of the Trp residue at position 214 was used to examine domain II. In addition, Trp-to-acrylodan resonance energy transfer was examined to probe interdomain spatial relationships during unfolding. Increasing the temperature to less than 50 degrees C or adding less than 1.0 M GdHCl resulted in an initial, reversible separation of domains I and II. Denaturation by heating to 70 degrees C or by adding 2.0 M GdHCl resulted in irreversible unfolding of domain II. Further denaturation of HSA by either method resulted in irreversible unfolding of domain I. These results clearly demonstrate that HSA unfolds by a pathway involving at least three distinct steps. The low detection limits and high information content of dual probe fluorescence should allow this technique to be used to study the unfolding behavior of entrapped or immobilized HSA.
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Affiliation(s)
- K Flora
- Department of Chemistry, Brock University, St. Catharines, Ontario L2S 3A1, Canada
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