GroEL is heat shock protein 60 (chaperonin) of E. coli cytosol, its functional unit is a cylindrical 14mers. It facilitate protein folding through hydrophobic interaction with unfolded polypeptide structure. But there is much debating in which form of unfolded polypeptide it binds, either totally unfolded one or partially structured (especially secondary structureed) one. We can see many different results reported in scientific papers, supporting different views.
In this paper, these authers use human digydrofolate reductase (DHFR) as a model system to explore in this argument. They used stopped-flow fluorescence spectrometer to see the kinetics of binding mode of unfolded DHFR and GroEL, and saw that there are three phases in this kind of binding, and it seems that all these three intermediates of DHFR can bind to GroEL, again get positive evidence for the idea that GroEL can recognize different conformation of protein. The authors also use NMR technique in amide proton-deuterium exchange to see if the secondary strucure of DHFR (majorly b-sheet) forms or not, and they saw that most of native b-sheet structure is formed during its binding to GroEL, now supporting that partially structured polypeptide can bind to GroEL.
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