title: Purification and characterization of the beta-trefoil fold protein barley alpha-amylase/subtilisin inhibitor overexpressed in Escherichia coli.
abstract: Barley alpha-amylase/subtilisin inhibitor (BASI) is a beta-trefoil fold protein related to soybean trypsin inhibitor (Kunitz) and inhibits barley alpha-amylase isozyme 2 (AMY2), which is de novo synthesized in the seed during germination. Recombinant BASI was produced in Escherichia coli in an untagged form (untagged rBASI), in two His(6)-tag forms (His(6)-rBASI and His(6)-Xa-rBASI), and in an intein-CBD-tagged form (rBASI (intein)). The yields per liter culture after purification were (i) 25 mgl(-1) His(6)-rBASI; (ii) 6 mgl(-1) rBASI purified after cleavage of His(6)-Xa-rBASI by Factor Xa; (iii) 3 mgl(-1) untagged rBASI; and (iv) 0.2 mgl(-1) rBASI after a chitin-column and autohydrolysis of the rBASI-intein-CBD. In Pichia pastoris, rBASI was secreted at 0.1 mgl(-1). The recombinant BASI forms and natural seed BASI (sBASI) all had an identical isoelectric point of 7.2 and a mass of 19,879 Da, as determined by mass spectrometry. The fold of rBASI from the different preparations was confirmed by circular dichroism spectroscopy and rBASI (intein), His(6)-rBASI, and sBASI inhibited AMY2 catalyzed starch hydrolysis with K(i) of 0.10, 0.06, and 0.09 nM, respectively. Surface plasmon resonance analysis of the formation of AMY2/rBASI (intein) gave k(on)=1.3x10(5)M(-1)s(-1), k(off)=1.4x10(-4)s(-1), and K(D)=1.1 nM, and of the savinase-His(6)-rBASI complex k(on)=21.0x10(4)M(-1)s(-1), k(off)=53.0x10(-4)s(-1), and K(D)=25.0 nM, in agreement with sBASI values. K(i) was 77 and 65 nM for inhibition of savinase activity by His(6)-rBASI and sBASI, respectively.
authors.affiliation: Department of Chemistry, Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK-2500 Copenhagen Valby, Denmark.
authors.forename: Birgit C
authors.initials: BC
authors.lastname: Bønsager
authors.forename: Mette
authors.initials: M
authors.lastname: Praetorius-Ibba
authors.forename: Peter K
authors.initials: PK
authors.lastname: Nielsen
authors.forename: Birte
authors.initials: B
authors.lastname: Svensson
mesh_terms: D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics*; D001467:Hordeum; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D010940:Plant Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000302:isolation & purification* / Q000378:metabolism / Q000494:pharmacology; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D020349:Surface Plasmon Resonance; D014360:Trypsin Inhibitor, Kunitz Soybean / Q000096:biosynthesis* / Q000235:genetics / Q000302:isolation & purification* / Q000494:pharmacology; D000516:alpha-Amylases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D010940:Plant Proteins; D011994:Recombinant Proteins; C092772:barley alpha-amylase-subtilisin inhibitor; D014360:Trypsin Inhibitor, Kunitz Soybean; C113880:AMY1.2 protein, Hordeum vulgare; D000516:alpha-Amylases