The crystal structure of plasminogen activator inhibitor 2 at 2.0 A resolution: implications for serpin function.
BACKGROUND
Plasminogen activator inhibitor 2 (PAI-2) is a member of the serpin family of protease inhibitors that function via a dramatic structural change from a native, stressed state to a relaxed form. This transition is mediated by a segment of the serpin termed the reactive centre loop (RCL); the RCL is cleaved on interaction with the protease and becomes inserted into betasheet A of the serpin. Major questions remain as to what factors facilitate this transition and how they relate to protease inhibition.


RESULTS
The crystal structure of a mutant form of human PAI-2 in the stressed state has been determined at 2.0 A resolution. The RCL is completely disordered in the structure. An examination of polar residues that are highly conserved across all serpins identifies functionally important regions. A buried polar cluster beneath betasheet A (the so-called 'shutter' region) is found to stabilise both the stressed and relaxed forms via a rearrangement of hydrogen bonds.


CONCLUSIONS
A statistical analysis of interstrand interactions indicated that the shutter region can be used to discriminate between inhibitory and non-inhibitory serpins. This analysis implied that insertion of the RCL into betasheet A up to residue P8 is important for protease inhibition and hence the structure of the complex formed between the serpin and the target protease.
Harrop
S J
SJ
Initiative in Biomolecular Structure, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia.
Jankova
L
L
Coles
M
M
Jardine
D
D
Whittaker
J S
JS
Gould
A R
AR
Meister
A
A
King
G C
GC
Mabbutt
B C
BC
Curmi
P M
PM
D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017396:Plasminogen Activator Inhibitor 2 / Q000737:chemistry* / Q000378:metabolism*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D015843:Serpins / Q000737:chemistry* / Q000378:metabolism*
D017396:Plasminogen Activator Inhibitor 2; D011994:Recombinant Proteins; D015843:Serpins