title: Irreversible denaturation of maltodextrin glucosidase studied by differential scanning calorimetry, circular dichroism, and turbidity measurements.
abstract: Thermal denaturation of Escherichia coli maltodextrin glucosidase was studied by differential scanning calorimetry, circular dichroism (230 nm), and UV-absorption measurements (340 nm), which were respectively used to monitor heat absorption, conformational unfolding, and the production of solution turbidity. The denaturation was irreversible, and the thermal transition recorded at scan rates of 0.5-1.5 K/min was significantly scan-rate dependent, indicating that the thermal denaturation was kinetically controlled. The absence of a protein-concentration effect on the thermal transition indicated that the denaturation was rate-limited by a mono-molecular process. From the analysis of the calorimetric thermograms, a one-step irreversible model well represented the thermal denaturation of the protein. The calorimetrically observed thermal transitions showed excellent coincidence with the turbidity transitions monitored by UV-absorption as well as with the unfolding transitions monitored by circular dichroism. The thermal denaturation of the protein was thus rate-limited by conformational unfolding, which was followed by a rapid irreversible formation of aggregates that produced the solution turbidity. It is thus important to note that the absence of the protein-concentration effect on the irreversible thermal denaturation does not necessarily means the absence of protein aggregation itself. The turbidity measurements together with differential scanning calorimetry in the irreversible thermal denaturation of the protein provided a very effective approach for understanding the mechanisms of the irreversible denaturation. The Arrhenius-equation parameters obtained from analysis of the thermal denaturation were compared with those of other proteins that have been reported to show the one-step irreversible thermal denaturation. Maltodextrin glucosidase had sufficiently high kinetic stability with a half-life of 68 days at a physiological temperature (37°C).
authors.affiliation: Okazaki Institute for Integrative Bioscience and Institute for Molecular Science, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi, 444-8787, Japan; School of Biological Sciences, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India.
authors.forename: Megha
authors.initials: M
authors.lastname: Goyal
authors.affiliation: School of Biological Sciences, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India.
authors.forename: Tapan K
authors.initials: TK
authors.lastname: Chaudhuri
authors.affiliation: Okazaki Institute for Integrative Bioscience and Institute for Molecular Science, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi, 444-8787, Japan; Department of Functional Molecular Science, School of Physical Sciences, the Graduate University for Advanced Studies (Sokendai), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi, 444-8787, Japan; The Center for the Promotion of Integrated Sciences (CPIS), the Graduate University for Advance Studies (Sokendai), Shonan Village, Hayama, Kanagawa, 240-0193, Japan; School of Computational Sciences, Korea Institute for Advanced Study (KIAS), Dongdaemun-gu, Seoul, 130-722, Korea.
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Kuwajima
mesh_terms: D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D006026:Glycoside Hydrolases / Q000737:chemistry*; D006207:Half-Life; D007700:Kinetics; D009391:Nephelometry and Turbidimetry; D066329:Protein Aggregates; D011487:Protein Conformation; D011489:Protein Denaturation; D013696:Temperature; D013816:Thermodynamics
chemical_list: D029968:Escherichia coli Proteins; D066329:Protein Aggregates; D006026:Glycoside Hydrolases; C071233:malZ protein, E coli