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Shahsavani MB, Hoshino M, Kumar A, Yousefi R. Charge manipulation of the human insulin B chain C-terminal to shed light on the complex mechanism of insulin fibrillation. Biochim Biophys Acta Gen Subj 2024; 1868:130578. [PMID: 38278307 DOI: 10.1016/j.bbagen.2024.130578] [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: 11/17/2023] [Revised: 01/13/2024] [Accepted: 01/23/2024] [Indexed: 01/28/2024]
Abstract
Insulin fibrillation poses a significant challenge in the development and treatment of diabetes. Current efforts to unravel its mechanisms have thus far remained incomplete. To shed light on the intricate processes behind insulin fibrillation, we employed mutagenesis techniques to introduce additional positive charge residues into the C-terminal region of the insulin B chain which plays an important role in insulin dimerization. We employed our investigation with various spectroscopic methods, electron microscopy, and molecular dynamics simulations. These methods allowed us to explore the structure and fibrillation behavior of the engineered B chains following their expression in a bacterial host and successful purification. This manipulation had a pronounced impact on the oligomerization behavior of the insulin B chain. It appears that these mutations delay the formation of the dimeric state in the process of transitioning to larger oligomers, consequently, leading to an alteration in the kinetics of fibrillation. Our findings also indicated that the mutant insulin B chains (Di-R, Di-K, and Di-H) displayed resistance to the initiation of fibrillation. This resistance can be attributed to the repulsive forces generated by the introduced positive charges, which disrupt the attractive interactions favoring nucleation. Notably, the mutant B chains formed shorter and less abundant oligomers and fibrils, which can be ascribed to the alterations induced by repulsion. Our engineered mutant B chains exhibited enhanced stability against stress-induced fibrillation, hinting at their potential utility in the development of new insulin analogs. This study underscores the significance of the C-terminal region in the initial stages of insulin B chain fibrillation, providing valuable insights into the intricate mechanisms involved and their potential pharmaceutical applications.
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Affiliation(s)
- Mohammad Bagher Shahsavani
- Protein Chemistry Laboratory (PCL), Department of Biology, College of Sciences, Shiraz University, Shiraz, Iran
| | - Masaru Hoshino
- Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto 606-8501, Japan
| | - Ashutosh Kumar
- Department of Biosciences and Bioengineering, IIT Bombay, Powai, Mumbai 400076, India
| | - Reza Yousefi
- Protein Chemistry Laboratory (PCL), Department of Biology, College of Sciences, Shiraz University, Shiraz, Iran; Institute of Biochemistry and Biophysics (IBB), University of Tehran, Tehran, Iran.
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2
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Distribution and Transition of Stable Conformations in Unfolding of Bovine Insulin Induced by Urea and Guanidine Hydrochloride. CHINESE JOURNAL OF ANALYTICAL CHEMISTRY 2020. [DOI: 10.1016/s1872-2040(20)60046-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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3
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Singh R, Bansal R, Rathore AS, Goel G. Equilibrium Ensembles for Insulin Folding from Bias-Exchange Metadynamics. Biophys J 2017; 112:1571-1585. [PMID: 28445749 DOI: 10.1016/j.bpj.2017.03.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Revised: 03/03/2017] [Accepted: 03/20/2017] [Indexed: 12/29/2022] Open
Abstract
Earliest events in the aggregation process, such as single molecule reconfiguration, are extremely important and the most difficult to characterize in experiments. To this end, we have used well-tempered bias exchange metadynamics simulations to determine the equilibrium ensembles of an insulin molecule under amyloidogenic conditions of low pH and high temperature. A bin-based clustering method that uses statistics accumulated in bias exchange metadynamics trajectories was employed to construct a detailed thermodynamic and kinetic model of insulin folding. The highest lifetime, lowest free-energy ensemble identified consisted of native conformations adopted by a folded insulin monomer in solution, namely, the R-, the Rf-, and the T-states of insulin. The lowest free-energy structure had a root mean square deviation of only 0.15 nm from native x-ray structure. The second longest-lived metastable state was an unfolded, compact monomer with little similarity to the native structure. We have identified three additional long-lived, metastable states from the bin-based model. We then carried out an exhaustive structural characterization of metastable states on the basis of tertiary contact maps and per-residue accessible surface areas. We have also determined the lowest free-energy path between two longest-lived metastable states and confirm earlier findings of non-two-state folding for insulin through a folding intermediate. The ensemble containing the monomeric intermediate retained 58% of native hydrophobic contacts, however, accompanied by a complete loss of native secondary structure. We have discussed the relative importance of nativelike versus nonnative tertiary contacts for the folding transition. We also provide a simple measure to determine the importance of an individual residue for folding transition. Finally, we have compared and contrasted this intermediate with experimental data obtained in spectroscopic, crystallographic, and calorimetric measurements during early stages of insulin aggregation. We have also determined stability of monomeric insulin by incubation at a very low concentration to isolate protein-protein interaction effects.
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Affiliation(s)
- Richa Singh
- Department of Chemical Engineering, Indian Institute of Technology Delhi, New Delhi, India
| | - Rohit Bansal
- Department of Chemical Engineering, Indian Institute of Technology Delhi, New Delhi, India
| | - Anurag Singh Rathore
- Department of Chemical Engineering, Indian Institute of Technology Delhi, New Delhi, India
| | - Gaurav Goel
- Department of Chemical Engineering, Indian Institute of Technology Delhi, New Delhi, India.
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4
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Saha S, Deep S. Glycerol inhibits the primary pathways and transforms the secondary pathway of insulin aggregation. Phys Chem Chem Phys 2016; 18:18934-48. [PMID: 27353748 DOI: 10.1039/c6cp02906j] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Aggregation of insulin initiated from the monomeric form proceeds via the secondary pathway of fragmentation. It was interesting to find that glycerol had the potential to transform the secondary pathway of aggregation from fragmentation to heterogeneous nucleation in a concentration dependent manner. Such a change in the secondary pathway was manifested by a change in the fibrillar morphology, wherein, longer fibrils were formed in the presence of glycerol. Glycerol could inhibit all the major steps of insulin aggregation. The analysis of the kinetic traces suggested that the inhibitory effect was most significant on the primary pathways, although secondary nucleation and elongation were also inhibited. In fact, at higher glycerol concentrations, the primary pathways were inhibited to such an extent that the majority of the aggregation was now driven by the secondary pathways. Our data suggest that glycerol binds to the early intermediates in the insulin aggregation pathway, and inhibits them from forming the aggregation competent species capable of elongation. As higher order species are formed in the aggregation pathway, the relative stabilization rendered by glycerol diminishes due to the exclusion of glycerol from the interface.
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Affiliation(s)
- Shivnetra Saha
- Department of Chemistry, Indian Institute of Technology, Hauz-Khas, New Delhi, Delhi, India.
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Sohma Y, Hua QX, Liu M, Phillips NB, Hu SQ, Whittaker J, Whittaker LJ, Ng A, Roberts CT, Arvan P, Kent SBH, Weiss MA. Contribution of residue B5 to the folding and function of insulin and IGF-I: constraints and fine-tuning in the evolution of a protein family. J Biol Chem 2009; 285:5040-55. [PMID: 19959476 DOI: 10.1074/jbc.m109.062992] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Proinsulin exhibits a single structure, whereas insulin-like growth factors refold as two disulfide isomers in equilibrium. Native insulin-related growth factor (IGF)-I has canonical cystines (A6-A11, A7-B7, and A20-B19) maintained by IGF-binding proteins; IGF-swap has alternative pairing (A7-A11, A6-B7, and A20-B19) and impaired activity. Studies of mini-domain models suggest that residue B5 (His in insulin and Thr in IGFs) governs the ambiguity or uniqueness of disulfide pairing. Residue B5, a site of mutation in proinsulin causing neonatal diabetes, is thus of broad biophysical interest. Here, we characterize reciprocal B5 substitutions in the two proteins. In insulin, His(B5) --> Thr markedly destabilizes the hormone (DeltaDeltaG(u) 2.0 +/- 0.2 kcal/mol), impairs chain combination, and blocks cellular secretion of proinsulin. The reciprocal IGF-I substitution Thr(B5) --> His (residue 4) specifies a unique structure with native (1)H NMR signature. Chemical shifts and nuclear Overhauser effects are similar to those of native IGF-I. Whereas wild-type IGF-I undergoes thiol-catalyzed disulfide exchange to yield IGF-swap, His(B5)-IGF-I retains canonical pairing. Chemical denaturation studies indicate that His(B5) does not significantly enhance thermodynamic stability (DeltaDeltaG(u) 0.2 +/- 0.2 kcal/mol), implying that the substitution favors canonical pairing by destabilizing competing folds. Whereas the activity of Thr(B5)-insulin is decreased 5-fold, His(B5)-IGF-I exhibits 2-fold increased affinity for the IGF receptor and augmented post-receptor signaling. We propose that conservation of Thr(B5) in IGF-I, rescued from structural ambiguity by IGF-binding proteins, reflects fine-tuning of signal transduction. In contrast, the conservation of His(B5) in insulin highlights its critical role in insulin biosynthesis.
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Affiliation(s)
- Youhei Sohma
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, USA
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Norrman M, Schluckebier G. Crystallographic characterization of two novel crystal forms of human insulin induced by chaotropic agents and a shift in pH. BMC STRUCTURAL BIOLOGY 2007; 7:83. [PMID: 18093308 PMCID: PMC2241603 DOI: 10.1186/1472-6807-7-83] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/21/2007] [Accepted: 12/19/2007] [Indexed: 11/10/2022]
Abstract
Background Insulin is a therapeutic protein that is widely used for the treatment of diabetes. Its biological function was discovered more than 80 years ago and it has since then been characterized extensively. Crystallization of the insulin molecule has always been a key activity since the protein is often administered by subcutaneous injections of crystalline insulin formulations. Over the years, insulin has been crystallized and characterized in a number of crystal systems. Results Interestingly, we have now discovered two new crystal forms of human insulin. The crystals were obtained when the two chaotropic agents, urea and thiocyanate were present in the crystallization experiments, and their structures were determined by X-ray crystallography. The crystals belong to the orthorhombic and monoclinic crystal systems, with space groups C2221 and C2 respectively. The orthorhombic crystals were obtained at pH 6.5 and contained three insulin hexamers in R6 conformation in the asymmetric unit whilst the monoclinic C2 crystals were obtained at pH 7.0 and contained one R6 hexamer in the asymmetric unit. Common for the two new crystals is a hexamer-hexamer interaction that has not been found in any of the previous crystal forms of insulin. The contacts involve a tight glutamate-glutamate interaction with a distance of 2.3 Å between groups. The short distance suggests a low barrier hydrogen bond. In addition, two tyrosine-tyrosine interactions occupying a known phenol binding pocket contribute to the stabilization of the contacts. Within the crystals, distinct binding sites for urea were found, adding further to the discussion on the role of urea in protein denaturation. Conclusion The change in space group from C2221 to C2 was primarily caused by an increase in pH. The fewer number of hexamer-hexamer interactions comprising the short hydrogen bond in the C2 space group suggest that pH is the driving force. In addition, the distance between the two glutamates increases from 2.32 Å in the C2221 crystals to 2.4 Å in the C2 crystals. However, in both cases the low barrier hydrogen bond and the tyrosine-tyrosine interaction should contribute to the stability of the crystals which is crucial when used in pharmaceutical formulations.
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Affiliation(s)
- Mathias Norrman
- Diabetes Protein Engineering, Novo Nordisk A/S, Novo Nordisk Park, DK-2760 Måløv, Denmark.
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7
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Fujimoto Y, Tanaka N, Kunugi S. Pre-incubation under High Pressure Accelerates Amyloid Formation from Insulin. Polym J 2006. [DOI: 10.1295/polymj.38.302] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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8
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Min CY, Qiao ZS, Feng YM. Unfolding of human proinsulin. Intermediates and possible role of its C-peptide in folding/unfolding. ACTA ACUST UNITED AC 2004; 271:1737-47. [PMID: 15096212 DOI: 10.1111/j.1432-1033.2004.04079.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have investigated the in vitro refolding process of human proinsulin (HPI) and an artificial mini-C derivative of HPI (porcine insulin precursor, PIP), and found that they have significantly different disulfide-formation pathways. HPI and PIP differ in their amino acid sequences due to the presence of the C-peptide linker found in HPI, therefore suggesting that the C-peptide linker may be responsible for the observed difference in folding behaviour. However, the manner in which the C-peptide contributes to this difference is still unknown. We have used both the disulfide scrambling method and a redox-equilibrium assay to assess the stability of the disulfide bridges. The results show that disulfide reshuffling is easier to induce in HPI than in PIP by the addition of thiol reagent. Thus, the C-peptide may affect the unique folding pathway of HPI by allowing the disulfide bonds of HPI to be easily accessible. The detailed processes of HPI unfolding by reduction of its disulfide bonds and by disulfide scrambling methods were also investigated. In the reductive unfolding process no accumulation of intermediates was detected. In the process of unfolding by disulfide scrambling, HPI gradually rearranged its disulfide bonds to form three major isomers G1, G2 and G3. The most abundant isomer, G1, contains the B7-B19 disulfide bridge. Based on far-UV CD spectra, native gel analysis and cleavage by endoproteinase V8, the G1 isomer has been shown to resemble the intermediate P4 found in the refolding process of HPI. Finally, the major isomer G1 is allowed to refold to native protein HPI by disulfide rearrangement, which indicates that a similar molecular mechanism may exist for the unfolding and refolding process of HPI.
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Affiliation(s)
- Cheng-Yin Min
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
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9
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Ahmad A, Millett IS, Doniach S, Uversky VN, Fink AL. Stimulation of Insulin Fibrillation by Urea-induced Intermediates. J Biol Chem 2004; 279:14999-5013. [PMID: 14736893 DOI: 10.1074/jbc.m313134200] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Fibrillar deposits of insulin cause serious problems in implantable insulin pumps, commercial production of insulin, and for some diabetics. We performed a systematic investigation of the effect of urea-induced structural perturbations on the mechanism of fibrillation of insulin. The addition of as little as 0.5 m urea to zinc-bound hexameric insulin led to dissociation into dimers. Moderate concentrations of urea led to accumulation of a partially unfolded dimer state, which dissociates into an expanded, partially folded monomeric state. Very high concentrations of urea resulted in an unfolded monomer with some residual structure. The addition of even very low concentrations of urea resulted in increased fibrillation. Accelerated fibrillation correlated with population of the partially folded intermediates, which existed at up to 8 m urea, accounting for the formation of substantial amounts of fibrils under such conditions. Under monomeric conditions the addition of low concentrations of urea slowed down the rate of fibrillation, e.g. 5-fold at 0.75 m urea. The decreased fibrillation of the monomer was due to an induced non-native conformation with significantly increased alpha-helical content compared with the native conformation. The data indicate a close-knit relationship between insulin conformation and propensity to fibrillate. The correlation between fibrillation and the partially unfolded monomer indicates that the latter is a critical amyloidogenic intermediate in insulin fibrillation.
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Affiliation(s)
- Atta Ahmad
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, USA
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10
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Yip CM, Brader ML, Frank BH, DeFelippis MR, Ward MD. Structural studies of a crystalline insulin analog complex with protamine by atomic force microscopy. Biophys J 2000; 78:466-73. [PMID: 10620310 PMCID: PMC1300654 DOI: 10.1016/s0006-3495(00)76609-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Crystallographic studies of insulin-protamine complexes, such as neutral protamine Hagedorn (NPH) insulin, have been hampered by high crystal solvent content, small crystal dimensions, and extensive disorder in the protamine molecules. We report herein in situ tapping mode atomic force microscopy (TMAFM) studies of crystalline neutral protamine Lys(B28)Pro(B29) (NPL), a complex of Lys(B28)Pro(B29) insulin, in which the C-terminal prolyl and lysyl residues of human insulin are inverted, and protamine that is used as an intermediate time-action therapy for treating insulin-dependent diabetes. Tapping mode AFM performed at 6 degrees C on bipyramidally tipped tetragonal rod-shaped NPL crystals revealed large micron-sized islands separated by 44-A tall steps. Lattice images obtained by in situ TMAFM phase and height imaging on these islands were consistent with the arrangement of individual insulin-protamine complexes on the P4(1)2(1)2 (110) crystal plane of NPH, based on a low-resolution x-ray diffraction structure of NPH, arguing that the NPH and NPL insulins are isostructural. Superposition of the height and phase images indicated that tip-sample adhesion was larger in the interstices between NPL complexes in the (110) crystal plane than over the individual complexes. These results demonstrate the utility of low-temperature TMAFM height and phase imaging for the structural characterization of biomolecular complexes.
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Affiliation(s)
- C M Yip
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285, USA.
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Yip CM, Yip CC, Ward MD. Direct force measurements of insulin monomer-monomer interactions. Biochemistry 1998; 37:5439-49. [PMID: 9548925 DOI: 10.1021/bi9722756] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Direct measurement of the forces involved in protein-protein and protein-receptor interactions can, in principle, provide insight necessary for the advancement of structural biology, molecular biology, and the development of therapeutic proteins. The protein insulin is illustrative in this respect as the mechanisms of insulin dimer dissociation and insulin-insulin receptor binding are crucial to the efficacy of insulin medications for the control of diabetes. Insulin molecules, modified with a photochemically active azido functionality on specific residues, were attached to force microscope tips and opposing mica surfaces in configurations that would either favor or disfavor dimer formation. Force curve measurements performed in buffer solution revealed the complexity of the insulin monomer-monomer interaction with multiple unbinding events occurring upon tip retraction, suggesting disruption of discrete molecular bonds at the monomer-monomer interface. Furthermore, the force curves exhibit long-range unbinding events, consistent with considerable elongation of the insulin molecule prior to dissociation. The unbinding forces observed in this study are the result of a combination of molecular disentanglement and dimer dissociation processes.
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Affiliation(s)
- C M Yip
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis 55455, USA
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12
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Effects of surface hydrophobicity on the structural properties of insulin. ACTA ACUST UNITED AC 1997. [DOI: 10.1016/s1080-8914(97)80030-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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13
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Bryant C, Spencer DB, Miller A, Bakaysa DL, McCune KS, Maple SR, Pekar AH, Brems DN. Acid stabilization of insulin. Biochemistry 1993; 32:8075-82. [PMID: 8394123 DOI: 10.1021/bi00083a004] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The effect of pH on the conformational stability of insulin was studied. Surprisingly, the Gibbs free energy of unfolding increased approximately 30% by acidification. pH titration of insulin's conformational stability is described by a transition involving a single proton with an apparent pK(a) of 7.0. The acid stabilization of insulin's conformation was attributed to the protonation of histidine at position 5 on the B-chain (HB5) as determined by 1H-NMR of the histidines, selective amino acid alteration, and enthalpies of ionization. Further acidification (at least to pH 2) does not decrease the free energy of unfolding. A conformational change in the tertiary structure, as indicated by the near-UV circular dichroism spectrum, accompanies this change in stability. We propose that this acid stabilization of insulin is physiologically important in maintaining insulin stability in the acid environment of the secretory/storage granules of the beta-cell of the pancreatic islets of Langerhans.
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Affiliation(s)
- C Bryant
- Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46285
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Powers ME, Matsuura J, Brassell J, Manning MC, Shefter E. Enhanced solubility of proteins and peptides in nonpolar solvents through hydrophobic ion pairing. Biopolymers 1993. [DOI: 10.1002/bip.360330608] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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