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Molecular Basis of Catalytic Chamber-assisted Unfolding and Cleavage of Human Insulin by Human Insulin-degrading EnzymeS
Ist Teil von
The Journal of biological chemistry, 2009-05, Vol.284 (21), p.14177-14188
Ort / Verlag
American Society for Biochemistry and Molecular Biology
Erscheinungsjahr
2009
Quelle
Free E-Journal (出版社公開部分のみ)
Beschreibungen/Notizen
Insulin is a hormone vital for glucose homeostasis, and insulin-degrading
enzyme (IDE) plays a key role in its clearance. IDE exhibits a remarkable
specificity to degrade insulin without breaking the disulfide bonds that hold
the insulin A and B chains together. Using Fourier transform ion cyclotron
resonance (FTICR) mass spectrometry to obtain high mass accuracy, and electron
capture dissociation (ECD) to selectively break the disulfide bonds in gas
phase fragmentation, we determined the cleavage sites and composition of human
insulin fragments generated by human IDE. Our time-dependent analysis of
IDE-digested insulin fragments reveals that IDE is highly processive in its
initial cleavage at the middle of both the insulin A and B chains. This
ensures that IDE effectively splits insulin into inactive N- and C-terminal
halves without breaking the disulfide bonds. To understand the molecular basis
of the recognition and unfolding of insulin by IDE, we determined a
2.6-Å resolution insulin-bound IDE structure. Our structure reveals that
IDE forms an enclosed catalytic chamber that completely engulfs and intimately
interacts with a partially unfolded insulin molecule. This structure also
highlights how the unique size, shape, charge distribution, and exosite of the
IDE catalytic chamber contribute to its high affinity (∼100 n
m
)
for insulin. In addition, this structure shows how IDE utilizes the
interaction of its exosite with the N terminus of the insulin A chain as well
as other properties of the catalytic chamber to guide the unfolding of insulin
and allowing for the processive cleavages.