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Acta Crystallogr Sect F Struct Biol Cryst Commun. 2012 Nov 1;68(Pt 11):1289-93. doi: 10.1107/S1744309112039085. Epub 2012 Oct 26.

Structure of the recombinant BPTI/Kunitz-type inhibitor rShPI-1A from the marine invertebrate Stichodactyla helianthus.

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Centro de Estudio de Proteínas, Facultad de Biología, Universidad de la Habana, Calle 25 No. 455, Havana 10400, Cuba.


The BPTI/Kunitz-type inhibitor family includes several extremely potent serine protease inhibitors. To date, the inhibitory mechanisms have only been studied for mammalian inhibitors. Here, the first crystal structure of a BPTI/Kunitz-type inhibitor from a marine invertebrate (rShPI-1A) is reported to 2.5 Å resolution. Crystallization of recombinant rShPI-1A required the salt-induced dissociation of a trypsin complex that was previously formed to avoid intrinsic inhibitor aggregates in solution. The rShPI-1A structure is similar to the NMR structure of the molecule purified from the natural source, but allowed the assignment of disulfide-bridge chiralities and the detection of an internal stabilizing water network. A structural comparison with other BPTI/Kunitz-type canonical inhibitors revealed unusual ϕ angles at positions 17 and 30 to be a particular characteristic of the family. A significant clustering of ϕ and ψ angle values in the glycine-rich remote fragment near the secondary binding loop was additionally identified, but its impact on the specificity of rShPI-1A and similar molecules requires further study.

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