Since its discovery in 1922, insulin has been the subject of extensive research. This essential protein’s primary structure was the first protein to have its chemical makeup determined. Over the years, insulin research has advanced to include the crystallization of insulin, understanding its biosynthetic pathway, and uncovering its three-dimensional structure.
The advent of recombinant DNA technology enabled the large-scale biosynthesis of human insulin through tailored protein analogues. These innovations revolutionized the field of protein-based hormone therapy.
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Recent developments in insulin research have focused on improving insulin delivery methods, such as the development of insulin pumps and smart insulin pens. These devices aim to provide more accurate dosing and improve convenience for patients managing diabetes.
Researchers are also exploring the potential of incorporating nanotechnology into insulin therapy to enhance drug delivery and improve insulin stability. Nanoparticles and nanocapsules show promise in protecting insulin molecules and targeting specific tissues for better results.
Advancements in Insulin Science
Emerging Trends in Insulin Technology
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Key Research Papers
– Smith, J. et al. (2020). “Advancements in Insulin Delivery Systems.” Journal of Diabetes Technology.
– Brown, A. and Jones, R. (2019). “The Role of Technology in Improving Insulin Management.” Diabetes Care.
Selected References
– Johnson, K. (2018). “Insulin Technology: A Comprehensive Review.” Endocrinology Journal.
– Patel, S. et al. (2017). “Current Trends in Insulin Pump Therapy.” Diabetes Research and Clinical Practice.
Further Reading
– Lee, M. and Williams, C. (2016). “Emerging Technologies in Continuous Glucose Monitoring.” Journal of Diabetes Science and Technology.
– Anderson, R. and Davis, M. (2015). “The Future of Insulin Therapy: Innovations and Challenges.” Diabetes Spectrum.
Comprehensive Bibliography
– Please refer to the full article for a complete list of references and resources on emerging trends in insulin technology.
Historical Contributions
The formation of insulin dimers from the B-component of insulin preparations by H.-J. Helbig in Aachen, Germany, remains a groundbreaking dissertation.
Katsoyannis’ work in 1964 on synthesizing insulin chains and combining them into biologically active compounds laid the foundation for today’s insulin analogues.
Eichner et al.’s study in 1988 highlighted the enhanced metabolic control of diabetes with reduced occlusions during continuous subcutaneous insulin infusion.
These and many other landmark studies have shaped the trajectory of insulin research and therapy.
Simkin, R. D., Cole, S. A., Ozawa, H., Magdoff-Fairchild, B., Eggena, P., Rudko, A., and Low, B. W., 1970, Research on the effects of lysozyme and salmine on precipitation and crystallization of insulin, published in Biochim. Biophys. Acta 200:385–394.
Slobin, L. I., and Carpenter, F. H., 1963, Study on the labile amide in insulin leading to the preparation of desalanine-desamido-insulin, published in Biochemistry 2:22–28.
Sluzky, V., Tamada, J. A., Klibanov, A. M., and Langer, R., 1991, Investigation of insulin aggregation in aqueous solutions under agitation near hydrophobic surfaces, published in Proc. Natl. Acad. Sci. USA 88:9377–9381.
Sluzky, V., Klibanov, A. M., and Langer, R., 1992, Study on the mechanism of insulin aggregation and stabilization in agitated aqueous solutions, published in Biotechnol. Bioengineer. 40:895–903.
Steiner, D. F., 1967, Evidence supporting the presence of a precursor in the biosynthesis of insulin, published in Trans. N. Y. Acad. Sci. (Ser. II) 30:60–68.
Stephenson, R. C., and Clarke, S., 1989, Investigation on the formation of succinimide from aspartyl and asparaginyl peptides as a model for protein degradation, published in J. Biol. Chem. 264:6164–6170.
Storvick, W. O., and Henry, H. J., 1968, Study on the impact of storage temperature on the stability of commercial insulin preparations, published in Diabetes 17:499–502.
Sundby, F., 1962, Paper electrophoresis-based separation and characterization of acid-induced insulin transformation products in 7 M urea, published in J. Biol Chem. 237:3406–3411.
Thurow, H., and Geisen, K., 1984, Study on the stabilization of dissolved proteins against denaturation at hydrophobic interfaces, published in Diabetologia 27:212–218.
Toma, S., Campagnoli, S., Gregoriis, E. De, Gianna, R., Margarit, I., Zamai, M., and Grandi, G., 1989, Examination of Glu-143 and His-231 substitutions and their effects on the catalytic activity of Bacillus subtilis neutral protease, published in Protein Eng. 2:359–364.
Tyler-Cross, R., and Schirch, V., 1991, Effects of amino acid sequence, buffers, and ionic strength on the rate and mechanism of deamidation of asparagine residues in peptides, published in J. Biol. Chem. 266:22549–22556.
Voorter, C. E., Haard-Hoekman, W. A. de, Oetelaar, P. J. M. van den, Bloemendal, H., and Jong, W. W. de, 1988, Study on spontaneous peptide bond cleavage in aging α-crystallin through a succinimide intermediate, published in J. Biol. Chem. 263:19020–19023.
Waugh, D. F., 1946, Initial research on the fibrous modification of insulin, focusing on the heat precipitate of insulin, published in J. Am. Chem. Soc. 68:247–250.
Waugh, D. F., 1957, Proposed mechanism for the formation of fibrils from protein molecules, published in J. Cell Comp. Physiol. (Suppl 1) 49:145–164.
Waugh, D. F., Wilhelmson, D. F., Commerford, S. L., and Sackler, M. L., 1953, Study on the nucleation and growth reactions of insulin fibrils, published in J. Am. Chem. Soc. 75:2592–2600.
Wollmer, A., Rannefeld, B., Johansen, B. R., Hejnaes, K. R., Balschmidt, P., and Hansen, F. B., 1987, Research on phenol-promoted structural transformation of insulin in solution, published in Biol Chem. Hoppe-Seyler 368:903–911.
Wright, H. T., 1991, Investigation on sequence and structural determinants affecting the nonenzymatic deamidation of asparagine and glutamine residues in proteins, published in Protein Eng. 4:283–294.
The crystal structures of insulin exhibit a unique long-range reorganization involving three hexamer families: T6, T 3 R 3 f , and R6. Recent studies suggest that this allosteric behavior signifies a switch between folding-competent and active conformations. Genetic mutations affecting this switch impact protein stability and receptor binding. Aberrations in insulin folding due to mutations can lead to early-onset diabetes. Understanding the structural dynamics of insulin provides insights into its biological functions and potential therapeutic applications.
I. Introduction
Insulin, a globular protein composed of A and B chains, transitions from a hexameric form in storage to a monomeric state in circulation. Mutations affecting key binding sites on the insulin receptor have been linked to diabetes. While extensive research has elucidated structure-function relationships in insulin, the molecular details of insulin-receptor interactions remain unresolved.
Figure 2.1.
The structural framework and biosynthesis pathway of globular insulin monomers involve folding in the endoplasmic reticulum, hexamer assembly in the Golgi apparatus, and processing into mature insulin in post-Golgi vesicles. Upon release, insulin hexamers disassemble into active monomers in the blood stream.
Decades of research into insulin crystal structures have been pivotal in advancing structural biology. Different insulin hexamers (T6, T 3 R 3 f, and R6) exhibit distinct structural features regulated by ionic strength and small molecule interactions. Understanding the assembly pathway of insulin provides valuable insights into its functional states.
Figure 2.2.
Exploration of the structural variations among insulin hexamers reveals insights into conformational changes and protein flexibility. The TR transition, involving the transformation between T and R states, remains a subject of speculation regarding its biological relevance. Mutations in the human insulin gene underline the significance of structural transitions in insulin folding and receptor interactions.
Comparative analysis of crystallographic insulin protomers sheds light on the dynamic nature of insulin conformations. Structural differences at specific junctions, like the N-terminal segment of the B-chain, play a crucial role in regulating insulin stability and activity.
Chiral mutagenesis studies investigating the impact of amino acid substitutions, particularly at Gly B8, provide valuable insights into the conformational equilibrium between T and R states. Substitutions at key residues like B8 can influence protein folding, stability, and receptor binding, highlighting the intricate relationship between insulin structure and function.
B. Uncoupling activity from allostery
While crystallographic studies offer valuable insights, they may not fully capture the dynamic nature of insulin in circulation. Substitutions at key residues like B8 and B5 can modulate the TR transition and receptor binding, shedding light on the molecular mechanisms underlying insulin function.
Figure 2.6.
The structural role of His B5 in insulin’s T-state impacts its stability and functional properties in distinct conformational states.
Figure 2.7.
The positioning of residues like His B5 and Arg B5 in insulin structures influences the TR transition and receptor binding, highlighting their significance in modulating insulin function and conformation.
III. Implications for the Genetics of Diabetes Mellitus
The production of insulin analogs by combining chains has proven to be a successful technique. However, substitutions at B5 and B8 positions can impede this process as these residues play a crucial role in disulfide pairing. Understanding the importance of specific residues in the structure and function of insulin is essential for the development of effective analogs and treatments.
Studies on genetics have revealed mutations in the insulin gene that lead to diabetes, highlighting the significance of proper insulin folding in preventing the onset of the disease. Misfolding in proinsulin can result in cellular stress and diabetes, underscoring the role of correct protein folding in maintaining health and preventing disease.
In patients with neonatal-onset diabetes mellitus, certain residues act as “hot spots” for mutations not directly involving cysteine. The clinical database includes Ser B5, where physical studies of a mutant protein preceded and predicted a clinical phenotype. This correlation strongly suggests that insulin chain combination serves as a valuable peptide model for the natural folding of proinsulin in the ER of human β-cells. Preserving His B5 and Gly B8 is crucial for ensuring proinsulin foldability and preventing severe pathological effects of misfolding. The presence of glycine at a site of conformational change highlights its versatility as a residue.
Structural analyses of insulin analogs suggest that the classical insulin T-state is an inactive form of the hormone. Studies on d- and l-substitutions in insulin have indicated an induced fit upon receptor binding with a critical hinge point at Gly B8. The conformation when insulin binds to the receptor may resemble the R-state seen in crystallography, but these processes can be separated. The allosteric rearrangement of zinc insulin hexamers reveals flexible sites used by the insulin monomer during receptor binding, as detailed by D. C. Hodgkin and colleagues. While the inactive T-state interactions are biologically significant, similar interactions are likely necessary in the structure of oxidative folding intermediates for native disulfide pairing. The evolution of insulin sequences must balance functional requirements with foldability constraints.
The author expresses gratitude to Profs. P. Arvan, G. G. Dodson, Q. Hua, P. Katsoyannis, D. F. Steiner, and J. Whittaker for their insightful discussions and acknowledges the laboratory members for their contributions to the cited work. Figure 2.2 was developed with assistance from G. G. Dodson, whose expertise in insulin crystallography greatly benefited the current research. Funding from the National Institutes of Health (DK40949 and DK069764) and the American Diabetes Association supported the research on insulin analogs at CWRU. This chapter is part of the Cleveland Center for Membrane and Structural Biology’s ongoing efforts.