Glycogen phosphorylase (GP) Flashcards

1
Q

structure

A

two identical subunits with two domains (N and C)

N-terminal domain has crevice = glycogen storage cite

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2
Q

N terminal crevice

A

only hold 4-5 units of linear portion of glycogen, where there is NO branching…. If there is a branch, cant fit in storage site.
SO WHy have a crevice?
a number of the breakdown steps, wont have to dissociate/reassociate the glycogen…. why is this good: this is more efficient…

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3
Q

Where is actve site

A

between the two domains (N and C) has a required PLP vit B6 cofactor. This cofactor/coenzyme is also a prosthetic group.

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4
Q

PLP in this enzyme

A

not used as an e- sink as it normally is,,,

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5
Q

Two GP structures

A
  1. phsphorylate A with a Pi bound to ser-14 at both subunits
    phosphrylate B, does not have serine that is phosphorylated.
  2. In A and B, Have two conformers, T and R.

MULTILAYER REGULATION

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6
Q

Why is GP regulation complex?

A

protecting a precious resource of glycogen, want to make sure you really want to use it

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7
Q

T state

A

has buried active site, cant get S in, so have low affinity.

R has AS accessible, so has high affinity, including mechanistic phosphate. (enzyme a little more open here)

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8
Q

mechanistic phosphate

A

different from regulatory phosphate at ser-14.

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9
Q

T to R conf change

A
  • When going from T to R, the tower helices will change position to give more favorable packing. This conf change keeps overall symmetry which is the MWC model

Ser-14 containing regulatory Pi strongly stabilizes the R state.

T to R also displaces and disorders the 280s Loop so that it no longer covers AS, which means AS is open and S can get in.

Also causes a rotation in Arg side chain, which increases the mechanistic Pi affinity (substrate affinity for mechanistic Pi) due to ion pairing.

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10
Q
A
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