Title
Secondary structural alterations in glucoamylase as an influence of protein aggregation
Author
Minhal Abidi, Afshin Iram, Mohammad Furkan, Aabgeena Naeem
Year
2017
Journal
Internation Journal of Biological Macromolecules
Abstract
Glucoamylase (EC 3.2.1.3) from Aspergillus niger possesses 31% α-helix, 36% β structure and rest aperiodic structure. A transition of glucoamylase in presence of varying concentrations of glyoxal (GO) and trifluoroethanol (TFE) studied by using multi-methodological approaches. At 20% GO, glucoamylase exists as molten globule state as evident by high tryptophan and ANS fluorescence, retention of secondary structure and loss of native tertiary structure. This state precedes the onset of the aggregation process and maximum is achieved at the highest concentration i.e. at 90% of GO. TFE, on increasing concentration up to 25% induces secondary structure transformation leading to accumulation of intermolecular β sheets, altered tryptophan environment, high ANS and ThT fluorescence resulting in the formation of glucoamylase aggregates. Isothermal colorimetric titration curve is sigmoidal, indicating the weak binding of TFE and glucoamylase. TEM studies showed that glucoamylase at 25% TFE exists as amorphous aggregates. Further, TFE at 70% causes inhibition of enzyme aggregates; the majority of secondary structures observed at this concentration are α helices. Alpha helices being the main key player relocates glucoamylase native environment as evident by CD, FTIR and TEM. Hence induction of β sheet promotes protein aggregation and α helices in protein inhibits aggregation.
Instrument
J-815
Keywords
Circular dichroism, Secondary structure, Tertiary structure, Chemical stability, Aggregation, Biochemistry