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Structural insights into the unique inhibitory mechanism of the silkworm protease inhibitor serpin18.

Guo PC, Dong Z, Zhao P, Zhang Y, He H, Tan X, Zhang W, Xia Q - Sci Rep (2015)

Bottom Line: Notably, this inhibitiory reaction results from the formation of an intermediate complex, which then follows for the digestion of protease and inhibitor into small fragments.This activity differs from previously reported modes of inhibition for serpins.Our findings have thus provided novel structural insights into the unique inhibitory mechanism of serpin18.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, 216, Tiansheng Road, Beibei, Chongqing 400716, People's Republic of China.

ABSTRACT
Serpins generally serve as inhibitors that utilize a mobile reactive center loop (RCL) as bait to trap protease targets. Here, we present the crystal structure of serpin18 from Bombyx mori at 1.65 Å resolution, which has a very short and stable RCL. Activity analysis showed that the inhibitory target of serpin18 is a cysteine protease rather than a serine protease. Notably, this inhibitiory reaction results from the formation of an intermediate complex, which then follows for the digestion of protease and inhibitor into small fragments. This activity differs from previously reported modes of inhibition for serpins. Our findings have thus provided novel structural insights into the unique inhibitory mechanism of serpin18. Furthermore, one physiological target of serpin18, fibroinase, was identified, which enables us to better define the potential role for serpin18 in regulating fibroinase activity during B. mori development.

No MeSH data available.


Related in: MedlinePlus

Mode of the reaction of serpin18 with cysteine protease.I, serpin18 (PDB code: 4R9I); E, cysteine protease (papain, PDB code: 1PPP); EI, Michaelis-like complex (constructed by docking the X-ray structures of serpin18 and papain); EI*, thioacyl-intermediate; E′, degraded protease and I′, degraded serpin18.
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f6: Mode of the reaction of serpin18 with cysteine protease.I, serpin18 (PDB code: 4R9I); E, cysteine protease (papain, PDB code: 1PPP); EI, Michaelis-like complex (constructed by docking the X-ray structures of serpin18 and papain); EI*, thioacyl-intermediate; E′, degraded protease and I′, degraded serpin18.

Mentions: Based on our structural observations and previous studies, we proposed a unique inhibitory model for serpin (Fig. 6). First, similar to the inhibition of trypsin by Manduca serpin 1B36, serpin18 interacts with the protease, and forms a initial noncovalent Michaelis-like complex that involves slight conformational changes within the body of protease and serpin18. Second, the active site of the protease then attacks the scissile bond V362–A363 in the RCL of serpin18. This reaction proceeds in a manner similar to that between serpins and serine protease, from an initial Michaelis complex to the acyl-intermediate complex, in which both the serpin and protease undergo conformational changes to accommodate the transformation. However, during the formation of the thioacyl-intermediate, the RCL of serpin18 cannot become inserted into the β-sheet A and drag the enzyme to the bottom of serpin18. Third, the active site of cysteine protease becomes structurally loosed, as a consequence of a conformational change, becomes susceptible to proteolysis and is then cleaved by other active enzymes. Meanwhile, the complex-bound serpin18 is degraded as a normal substrate. Finally, the thioester bond in the thioacyl-intermediate is hydrolyzed, resulting in the degradation of serpin18 and cysteine protease.


Structural insights into the unique inhibitory mechanism of the silkworm protease inhibitor serpin18.

Guo PC, Dong Z, Zhao P, Zhang Y, He H, Tan X, Zhang W, Xia Q - Sci Rep (2015)

Mode of the reaction of serpin18 with cysteine protease.I, serpin18 (PDB code: 4R9I); E, cysteine protease (papain, PDB code: 1PPP); EI, Michaelis-like complex (constructed by docking the X-ray structures of serpin18 and papain); EI*, thioacyl-intermediate; E′, degraded protease and I′, degraded serpin18.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493575&req=5

f6: Mode of the reaction of serpin18 with cysteine protease.I, serpin18 (PDB code: 4R9I); E, cysteine protease (papain, PDB code: 1PPP); EI, Michaelis-like complex (constructed by docking the X-ray structures of serpin18 and papain); EI*, thioacyl-intermediate; E′, degraded protease and I′, degraded serpin18.
Mentions: Based on our structural observations and previous studies, we proposed a unique inhibitory model for serpin (Fig. 6). First, similar to the inhibition of trypsin by Manduca serpin 1B36, serpin18 interacts with the protease, and forms a initial noncovalent Michaelis-like complex that involves slight conformational changes within the body of protease and serpin18. Second, the active site of the protease then attacks the scissile bond V362–A363 in the RCL of serpin18. This reaction proceeds in a manner similar to that between serpins and serine protease, from an initial Michaelis complex to the acyl-intermediate complex, in which both the serpin and protease undergo conformational changes to accommodate the transformation. However, during the formation of the thioacyl-intermediate, the RCL of serpin18 cannot become inserted into the β-sheet A and drag the enzyme to the bottom of serpin18. Third, the active site of cysteine protease becomes structurally loosed, as a consequence of a conformational change, becomes susceptible to proteolysis and is then cleaved by other active enzymes. Meanwhile, the complex-bound serpin18 is degraded as a normal substrate. Finally, the thioester bond in the thioacyl-intermediate is hydrolyzed, resulting in the degradation of serpin18 and cysteine protease.

Bottom Line: Notably, this inhibitiory reaction results from the formation of an intermediate complex, which then follows for the digestion of protease and inhibitor into small fragments.This activity differs from previously reported modes of inhibition for serpins.Our findings have thus provided novel structural insights into the unique inhibitory mechanism of serpin18.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, 216, Tiansheng Road, Beibei, Chongqing 400716, People's Republic of China.

ABSTRACT
Serpins generally serve as inhibitors that utilize a mobile reactive center loop (RCL) as bait to trap protease targets. Here, we present the crystal structure of serpin18 from Bombyx mori at 1.65 Å resolution, which has a very short and stable RCL. Activity analysis showed that the inhibitory target of serpin18 is a cysteine protease rather than a serine protease. Notably, this inhibitiory reaction results from the formation of an intermediate complex, which then follows for the digestion of protease and inhibitor into small fragments. This activity differs from previously reported modes of inhibition for serpins. Our findings have thus provided novel structural insights into the unique inhibitory mechanism of serpin18. Furthermore, one physiological target of serpin18, fibroinase, was identified, which enables us to better define the potential role for serpin18 in regulating fibroinase activity during B. mori development.

No MeSH data available.


Related in: MedlinePlus