The structure of active serpin 1K from Manduca sexta.
BACKGROUND
The reactive center loops (RCL) of serpins undergo large conformational changes triggered by the interaction with their target protease. Available crystallographic data suggest that the serpin RCL is polymorphic, but the relevance of the observed conformations to the competent active structure and the conformational changes that occur on binding target protease has remained obscure. New high-resolution data on an active serpin, serpin 1K from the moth hornworm Manduca sexta, provide insights into how active serpins are stabilized and how conformational changes are induced by protease binding.


RESULTS
The 2.1 A structure shows that the RCL of serpin 1K, like that of active alpha1-antitrypsin, is canonical, complimentary and ready to bind to the target protease between P3 and P3 (where P refers to standard protease nomenclature),. In the hinge region (P17-P13), however, the RCL of serpin 1K, like ovalbumin and alpha1-antichymotrypsin, forms tight interactions that stabilize the five-stranded closed form of betasheet A. These interactions are not present in, and are not compatible with, the observed structure of active alpha1-antitrypsin.


CONCLUSIONS
Serpin 1K may represent the best resting conformation for serpins - canonical near P1, but stabilized in the closed conformation of betasheet A. By comparison with other active serpins, especially alpha1-antitrypsin, a model is proposed in which interaction with the target protease near P1 leads to conformational changes in betasheet A of the serpin.
Li
J
J
Department of Biochemistry, The University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75235, USA.
Wang
Z
Z
Canagarajah
B
B
Jiang
H
H
Kanost
M
M
Goldsmith
E J
EJ
D000595:Amino Acid Sequence; D000818:Animals; D003198:Computer Simulation; D003460:Crystallization; D018402:Manduca; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015843:Serpins / Q000737:chemistry*
D011994:Recombinant Proteins; D015843:Serpins