Structure of a post-translationally processed heterodimeric double-headed Kunitz-type serine protease inhibitor from potato

Abstract

Potato serine protease inhibitor (PSPI) constitutes about 22% of the total amount of proteins in potato tubers (cv. Elkana), making it the most abundant protease inhibitor in the plant. PSPI is a heterodimeric double-headed Kunitz-type serine protease inhibitor that can tightly and simultaneously bind two serine proteases by mimicking the substrate of the enzyme with its reactive-site loops. Here, the crystal structure of PSPI is reported, representing the first heterodimeric double-headed Kunitz-type serine protease inhibitor structure to be determined. PSPI has a β-trefoil fold and, based on the structure, two reactive-site loops bearing residues Phe75 and Lys95 were identified.

Structures of a bi-functional Kunitz-type STI family inhibitor of serine and aspartic proteases: Could the aspartic protease inhibition have evolved from a canonical serine protease-binding loop?

“…S3). A similar prediction was made for inhibitor PSPI (PDB code: 3TC2), which has been proved to be a monomer in solution (Meulenbroek et al, 2012).…”

“…3.4.21.1), human leukocyte elastase (EC 3.4.21.37), human and bovine cathepsin D (EC 3.4.23.5) and Saccharopepsin (EC 3.4.21.41) (Cater et al, 2002;Pouvreau et al, 2001). The sequence identity of E3Ad with other inhibitors of the Kunitz-type STI family characterized so far are: PDI (90.4%) (Keilová and Tomášek, 1976a), SLAPI (76.1%) (Cater et al, 2002), PSPI (71.2%) (Meulenbroek et al, 2012), Murraya koenigii miraculin-like protein (27.7%) (Gahloth et al, 2010), TKI (26.1%) (Patil et al, 2012) EcTI (25.5%) (Zhou et al, 2013), API-A (24.5%) (Bao et al, 2009), BASI (23.6%) (Vallée et al, 1998) and STI (22.6%) (Song and Suh, 1998). Details of amino acid substitutions in key regions for Kunitz-type STI inhibitors are shown in Fig.…”

Purification and characterization of a newly serine protease inhibitor from Rhamnus frangula with potential for use as therapeutic drug

“…Based on their amino acid sequences, eight classes of plant serine protease inhibitors were reported (Mosolov and Valueva 2005). Among them, protease inhibitor 1, protease inhibitor 2, and soybean trypsin inhibitor families were well studied (Kim et al 2009;Meulenbroek et al 2012). Almost all the previously studied serine protease inhibitors are isolated from Solanaceae, Fabaceae, Euphorbiaceae, Poaceae, and Cucurbitaceae families.…”

Juggling jobs: roles and mechanisms of multifunctional protease inhibitors in plants

“…Potato (Solanum tuberosum L.) tubers also contain a Janus-type Kunitz type inhibitor, named potato serine protease inhibitor (PSPI). PSPI can bind simultaneously to both trypsin and chymotrypsin, two S1 Ser proteases with different substrate specificities (Valueva et al, 2000;Meulenbroek et al, 2012). The biological role of PSPI in planta is unclear.…”

“…In principle, PSPI could act in defence or protect storage proteins from endogenous proteases to prevent premature sprouting. Considering that PSPI is one of the most abundant proteins in potato tubers (Meulenbroek et al, 2012), it probably also serves as a storage protein itself. Recently, a new biochemical function was proposed for Kunitz trypsin inhibitor 3 (KTI3), a Populus deltoides (poplar) inhibitor from the Kunitz family active against trypsin and chymotrypsin (Major & Constabel, 2008).…”